INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 72
PRINCIPLES OF STUDIES ON DISEASES OF SUSPECTED
CHEMICAL ETIOLOGY AND THEIR PREVENTION
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1987
The International Programme on Chemical Safety (IPCS) is a
joint venture of the United Nations Environment Programme, the
International Labour Organisation, and the World Health
Organization. The main objective of the IPCS is to carry out and
disseminate evaluations of the effects of chemicals on human health
and the quality of the environment. Supporting activities include
the development of epidemiological, experimental laboratory, and
risk-assessment methods that could produce internationally
comparable results, and the development of manpower in the field of
toxicology. Other activities carried out by the IPCS include the
development of know-how for coping with chemical accidents,
coordination of laboratory testing and epidemiological studies, and
promotion of research on the mechanisms of the biological action of
chemicals.
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CONTENTS
PRINCIPLES OF STUDIES ON DISEASES OF SUSPECTED CHEMICAL ETIOLOGY
AND THEIR PREVENTION
INTRODUCTION
1. SUMMARY
2. DEFINITION OF THE PROBLEM
3. GENERAL APPROACHES IN THE INVESTIGATION OF DISEASES OF
SUSPECTED CHEMICAL ETIOLOGY
4. DISEASE APPROACH: RECOGNITION AND DESCRIPTION OF A HEALTH
PROBLEM
4.1. General background
4.2. Recognition of the index cases
4.3. Screening of populations for suspected cases
4.4. Case definition
4.5. Case identification
4.6. Importance of pathological studies
4.7. Reporting systems and case records
5. EPIDEMIOLOGICAL APPROACHES: SEARCH FOR DETERMINANTS
5.1. General background
5.2. Collection of information and criteria for obtaining
specimens
5.3. In-depth study of cases
5.4. Evaluation of epidemiological data
6. TOXICOLOGICAL APPROACHES: STUDIES ON CHEMICALS POSSIBLY
INVOLVED
6.1. Experimental animal studies
6.2. Analysis for toxic substances
6.3. Toxic chemical information data systems
7. PROBLEMS IN ESTABLISHING CHEMICAL ETIOLOGY
7.1. Causation in human disease
7.2. Consideration of a chemical etiology
7.3. Temporal relationships
7.4. Biological plausibility
7.5. Dose-response and dose-effect relationships
7.6. Effects of intervention
7.7. Confirmation of a causal relationship
8. STEPS TO BE TAKEN FOLLOWING THE RECOGNITION OF THE CHEMICAL
ETIOLOGY OF AN OUTBREAK
8.1. Preventive action and control
8.2. Surveillance and monitoring system
8.3. Health education
9. THE NEED FOR INTERNATIONAL COOPERATION
9.1. Cooperation and collaboration among countries
9.2. Global and regional activities
9.3. Final recommendations
REFERENCES
APPENDIX I. LIST OF BACKGROUND PAPERS
APPENDIX II. CONCEPTUAL FRAMEWORK USED IN SEVERAL STUDIES
LEADING TO IDENTIFICATION OF THE CHEMICAL
ETIOLOGY OF OUTBREAKS OF DISEASES
APPENDIX III. SUMMARY REPORT ON THE IPCS/WPRO/PRC MEETING
ON KASHIN-BECK DISEASE
WHO TASK GROUP ON PRINCIPLES OF STUDIES ON DISEASES OF SUSPECTED
CHEMICAL ETIOLOGY AND THEIR PREVENTION
Members
a,c Professor L. Amin-Zaki, Former Professor of Paediatrics
(Baghdad), Abu Dhabi, United Arab Emirates
a Professor E.A. Bababunmi, Laboratory of Biomembrane
Research, Department of Biochemistry, University of
Ibadan, College of Medicine, Ibadan, Nigeria
a Dr R.V. Bhat, National Institute of Nutrition, Indian
Council of Medical Research, Hyderabad, India
a,b,d Dr J. Borgoño, University of Chile, Department of
International Affairs, Ministry of Health, Santiago,
Chile (Vice-Chairman)
a Dr Y. Egashira, National Institute of Health, Hatano
Research Institute, Food and Drug Research Centre,
Hatanoshi, Kanagawa-ken, Japan
a,b,d Dr R.A. Goyer, National Institute of Environmental
Health Sciences, Research Triangle Park, North
Carolina, USA
a,c,d Dr P. Grandjean, Institute of Community Health,
Department of Environmental Medicine, Odense
University, Odense, Denmark
a Dr V.N. Ivanov, Chita Medical Institute, Chita, USSR
a Dr V.V. Ivanov, Department of Pathophysiology,
Krasnoyarsk Medical Institute, Krasnoyarsk, USSR
a,b,e Dr R.D. Kimbrough, Center for Environmental Health,
Centers for Disease Control, Atlanta, Georgia, USA
a,d Professor P. Krogh, Department of Microbiology, Royal
Dental College, Copenhagen, Denmark (Rapporteur)
a,c Dr O.A. Levander, Vitamin and Mineral Nutrition
Laboratory, Human Nutrition Research Center, US
Department of Agriculture, Beltsville, Maryland, USA
a,c Dr K.R. Mahaffey, Division of Standards Development
and Technology Transfer, National Institute for
Occupational Safety and Health, Cincinnati, Ohio, USA
a,d Dr G. Martin-Bouyer, Ministère de la Santé, Direction
Générale de la Santé, Paris, France (Rapporteur)
a Professor V.A. Nasonova, Institute of Rheumatology,
Academy of Medical Sciences of the USSR, Moscow, USSR
a,d Professor H.D. Tandon, New Delhi, India (Temporary
Adviser) (Chairman)
a Professor Yan Jianbo, Haerbin Medical University,
Haerbin, People's Republic of China
a,b Professor H. Yanagawa, Department of Public Health,
Jichi Medical School, Minamikawachi, Tochigi-ken,
Japan
a Professor Yang Guangqi, Institute of Health, China
National Centre for Preventive Medicine, Beijing,
People's Republic of China (Vice-Chairman)
a Professor Yu Weihan, Haerbin Medical University,
Haerbin, People's Republic of China
Observers
a Dr Chen Junshi, Department of Nutrition and Food
Hygiene, Institute of Health, China National Centre
for Preventive Medicine, Beijing, People's Republic
of China
a Dr Chen Xiaoshu, Institute of Health, China National
Centre for Preventive Medicine, Beijing, People's
Republic of China
a Dr Chen Qing, Department of Environmental Health,
School of Public Health, Beijing Medical University,
Beijing, People's Republic of China
a Dr Dai Yin, National Institute of Food Safety Control
and Inspection, China National Centre for Preventive
Medicine, Beijing, People's Republic of China
a Dr He Xingzhou, Department of Environmental Hygiene,
Institute of Health, China National Centre for
Preventive Medicine, Beijing, People's Republic of
China
a Dr Li Guangshen, Institute of Endemic Disease, Norman
Bethune University of Medical Sciences, Changchun,
Jilin province, People's Republic of China
a Professor Li Yurui, Division of Pneumoconiosis, Department
of Labour Hygiene, Institute of Health, China National
Centre for Preventive Medicine, Beijing, People's
Republic of China
a Dr Liu Yuying, Division of Industrial Toxicology,
Department of Labour Hygiene, Institute of Health,
China National Centre for Preventive Medicine,
Beijing, People's Republic of China
a Dr Lu Boqin, Division of Industrial Toxicology, Department
of Labour Hygiene, Institute of Health, China National
Centre for Preventive Medicine, Beijing, People's
Republic of China
a Dr Ma Tai, Tianjin Medical College, Tianjin, People's
Republic of China
a Professor Niu Shiru, Institute of Health, China
National Centre for Preventive Medicine, Beijing,
People's Republic of China
a Dr Qin Yuhui, Institute for Environmental Health
Monitoring, China National Centre for Preventive
Medicine, Beijing, People's Republic of China
a Dr Su Zhi, Department of Health and Epidemiological
Control, Ministry of Public Health, Beijing,
People's Republic of China
a Professor Tan Jianan, Institute of Geography, Chinese
Academy of Sciences, Beijing, People's Republic of
China
a Professor Wang Huizhou, Department of Nutrition and
Food Hygiene, Institute of Health, China National
Centre for Preventive Medicine, Beijing, People's
Republic of China
a Dr Wang Juning, Division of Environmental Toxicology,
Department of Environmental Hygiene, Institute of
Health, China National Centre for Preventive
Medicine, Beijing, People's Republic of China
a Dr Xu Genlin, Office of Research Management, Institute
of Health, China National Centre for Preventive
Medicine, Beijing, People's Republic of China
a Dr Xu Guanglu, Research Laboratory of Keshan Disease,
Xian Medical University, Xian, People's Republic of
China
a Dr Yo Peipei, Division of Pneumoconiosis, Department
of Labour Hygiene, Institute of Health, China
National Centre for Preventive Medicine, Beijing,
People's Republic of China
a Dr Zhen Xiwen, Institute of Epidemiology and Microbiology,
China National Centre for Preventive Medicine, Beijing,
People's Republic of China
Secretariat
e Dr T. Kjellström, Prevention of Environmental Pollution,
World Health Organization, Geneva, Switzerland
a Dr M. Mercier, International Programme on Chemical
Safety, World Health Organization, Geneva,
Switzerland
a Dr M. Mitrofanov, Division of Noncommunicable
Diseases, World Health Organization, Geneva,
Switzerland
a,d Dr J. Parizek, International Programme on Chemical
Safety, World Health Organization, Geneva,
Switzerland (Secretary)
d Dr A. Prost, Division of Environmental Health, World
Health Organization, Geneva, Switzerland
-------------------------------------------------------------------
a Attended the Task Group meeting in Beijing, 28 October -
2 November 1985.
b Chairman of a subgroup of the Beijing Task Group meeting.
c Rapporteur of a subgroup of the Beijing Task Group meeting.
d Attended the editorial meeting in Geneva, 28 April - 2 May 1986.
e Available for discussions at the Geneva editorial meeting on a
part-time basis.
NOTE TO READERS OF THE CRITERIA DOCUMENTS
Every effort has been made to present information in the
criteria documents as accurately as possible without unduly
delaying their publication. In the interest of all users of the
environmental health criteria documents, readers are kindly
requested to communicate any errors that may have occurred to the
Manager of the International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland, in order that they may be
included in corrigenda, which will appear in subsequent volumes.
* * *
INTRODUCTION
The prevention and control of locally endemic diseases is one
of the essential components of primary health care. The IPCS
Environmental Health Criteria documents dealing with mycotoxins
(WHO, 1979b), aquatic biotoxins (WHO, 1984b), and pyrrolizidine
alkaloids (WHO, in press), describe situations in which the
prevention and control of outbreaks of locally-occurring diseases
were made possible by the successful elucidation of the chemical
etiology of the diseases. The strategies used in this disease-
oriented approach, including the sequence and character of the
questions addressed, differ from those used in predictive
toxicology, where the starting point is not a disease but a known,
defined chemical, evaluated for possible health effects.
When developing the methodology component of the International
Programme on Chemical Safety, it was evident that there was a need
for a document that would summarize the principles of studies aimed
at the elucidation of the role of chemicals in the etiology of
diseases, benefiting from the experience of experts who have
successfully carried out such studies. The disease-oriented
approach in relation to chemical exposures and malignant and
occupational diseases has been dealt with in other programmes of
the World Health Organization (WHO), including the International
Agency for Research on Cancer (IARC), and will not be discussed
specifically in this document. The document focuses on the
principles of studies dealing with endemic non-malignant diseases
and outbreaks of diseases of unknown origin and the possible role
of exposure to chemicals in their causation.
Situations in which populations are permanently resident in an
area and mainly dependent on locally produced food, offer
conditions favourable for the occurrence of locally endemic
diseases and also for the study of these diseases. These
conditions are often found in developing countries and much can be
learned concerning methods of studying the problem of the chemical
etiology of diseases, from studies carried out in such regions.
Thus, it was of great advantage that the Ministry of Public Health
of the People's Republic of China agreed that the Institute of
Preventive Medicine and its Institute of Health, Beijing, would
host the IPCS Task Group meeting on the principles and criteria for
establishing the chemical etiology of diseases of uncertain
causality as a basis for their prevention, together with a joint
conference on Kashin-Beck disease, a highly disabling disease of
permanent character affecting a very large group of people in
endemic areas in China.
The resulting draft document was finalized at an editorial
meeting held in Geneva from 28 April to 2 May 1986 under the
guidance of PROFESSOR H.D. TANDON (Chairman of the Task Group).
Background papers, prepared by the participants at the request of
the Secretariat, for the IPCS Task Group meeting in Beijing, are
listed in Appendix I. The Chairman of the Task Group, responding
to a request of the Secretariat, prepared another paper summarizing
the conceptual framework that had been used in several studies in
the past and had led to the successful identification of the
chemical etiology of certain diseases and their prevention and
control. This paper, which was used as a guide for the Task Group
during discussions in plenary and subgroups and was further
developed at the editorial meeting, is presented in Appendix II.
The summary report of the Beijing meeting, reviewing the experience
on Kashin-Beck disease, is presented in Appendix III.
The help of the host Institutions in Beijing, the organizers of
the meetings, and all participants, including those who finalized
the document at the editorial meeting in Geneva, is gratefully
acknowledged. It is hoped that their life-long experience and
enthusiastic involvement throughout the preparation of this
publication will make it useful to all concerned with the
prevention and control of diseases of possible chemical etiology.
The United Kingdom Department of Health and Social Security
generously supported the costs of printing.
1. SUMMARY
It is suspected that some endemic diseases or sudden outbreaks
of unknown diseases in several regions of the world might be
related to exposure of affected populations to one or more natural
or man-made chemical substances.
This publication is based on experience from studies and
investigations in which the chemical origin of several unknown or
unusual pathological conditions has been successfully identified.
The basic principles of these studies are summarized and a step-
by-step approach is described starting with the recognition of the
disease pattern among the affected people, evaluation of the
magnitude of the problem (number of people affected, geographical
impact area, etc.), and collection of clues pointing to, and
eventual identification of, its chemical etiology. Such an
approach is called the disease approach. The search for etiology
begins after the recognition and description of the health problem
being investigated.
The second section of the paper deals with the epidemiological
approach. The search for specific determinants is described,
including methods that should be used, and how data should be
analysed. This is followed by a description of the toxicological
studies necessary for testing hypotheses on possible exposure to
various substances, the hypotheses having been generated through
the combined evaluation of clinical and epidemiological data.
Problems, including bias, in establishing the causal relationship
between one or several suspected agents and the observed disease
patterns are also considered.
A further section deals with steps that, in the opinion of the
Task Group, should be taken when the chemical etiology of an
outbreak of a disease has been recognized. The publication ends
with a section on the need for international cooperation in the
field of recognition of the chemical etiology of certain diseases.
A sequential list of activities that has been followed in
several successful studies and can be used as a checklist, when a
similar approach needs to be developed, is included as Appendix II.
The meeting at which this publication was prepared was held in
the People's Republic of China together with another international
meeting organized jointly by the IPCS, the WHO Regional Office for
the Western Pacific, and the health authorities of the People's
Republic of China. The second meeting dealt with the present
status of research on Kashin-Beck disease, and osteoarthrosis
deformation, which is endemic in certain parts of Asia and, in
certain regions of the People's Republic of China, has affected
more than one million inhabitants, mainly children. This disease
is given special attention, because it affects a very large segment
of the population in a developing country and because of growing
evidence that deficiency of a certain essential nutrient combined
with exposure to a specific chemical may be the factor responsible
for this peculiar disease and its specific endemicity.
2. DEFINITION OF THE PROBLEM
The prevention of disease constitutes a major component in
world-wide efforts to achieve "Health for all by the year 2000".
Preventive measures must be directed towards the control or
eradication of specific etiological factors that cause human
diseases. Thus, a prerequisite for successful prevention is
adequate knowledge concerning disease causation.
While several diseases are known to be heritable and therefore
to have a genetic etiology, other diseases are known to be caused
by specific environmental factors, as in the case of intoxications,
infections, or nutritional deficiencies. However, at present, the
etiology of most human diseases is not known or is only partially
known, and methods for primary prevention based on recognition of
etiology can only be considered for a limited number of diseases.
The search for etiological factors will therefore achieve
increasing importance as a basis for future preventive measures.
In this regard, diseases caused by chemical factors are of
particular interest, and their effects on human health have not
been sufficiently investigated, even though exposure to naturally-
occurring chemicals has always been a part of human life. With
further industrialization as an essential step in development,
people are likely to be exposed to more and increasingly diverse
chemicals, even though careful steps may be taken to monitor and
control their proper use and the safe disposal of industrial
wastes. New chemicals are developed for a variety of purposes,
both industrial and non-industrial, and the lack of preventive
measures, or insufficient application of such measures, may result
in toxic effects in populations exposed to them. Furthermore,
exposure to chemicals or combinations of chemicals under various
conditions of human life may result in toxic effects, not
previously recognized. Chemicals in the form of fertilizers and
pesticides are particularly essential in modern agriculture, to
meet the increasing needs for food, and exposure of the general
population to the residues of these chemicals is increasing. In
most parts of the world, the agricultural community is often not
sufficiently informed about the proper use of chemicals and the
associated hazards, and dangerous exposures are likely. The
episode of alkylmercury poisoning (WHO, 1977) is an example of
large-scale casualties caused by such accidents.
Exposure to chemicals may cause human disease in several ways.
First, a certain disease may result directly from exposure to a
specific chemical compound, for example, Minamata disease, which is
caused by exposure to methylmercury (WHO, 1977). Second, exposure
to a chemical may be only one of several factors contributing to
the development of a disease, and, thus, be part of a multicausal
relationship. Itai-itai disease is an example of a disease with a
complex etiology, caused by several factors in combination with
cadmium toxicity (Tsuchiya, 1978). Chemical exposure may also
aggravate a pre-existing disease. For example, air pollution with
nitrogen oxides will provoke air-way symptoms in patients with
respiratory diseases (WHO, 1979a). Thus, exposure to chemicals may
constitute a leading factor in the development of a range of human
diseases.
An important determinant of health is the balance between the
status of the milieu intérieur and that of the milieu extérieur.
Excess or deficiency of naturally-occurring chemicals in the
natural environment or the presence of extraneous chemicals may
alter this balance by making the body tissues more vulnerable.
Fluorosis is known to be endemic in several parts of the world
because of excess fluorides in the drinking-water; similarly, there
are large areas where goitre is endemic, because of iodine
deficiency in the environment. Nutritional factors play an
important role in both exposure and susceptibility to various
chemical agents.
The practising physician may not be familiar with the ever
increasing diversity of chemicals that can be hazardous for man,
nor with the initial symptoms and signs of toxicity. This is one
of the reasons why the establishment of a cause and effect
relationship between disease and exposure to chemical agents is
less straightforward than between disease and infections. Episodes
of chemical poisoning in the form of isolated cases, groups of
cases, or outbreaks, which present a pattern of disease that does
not fit in with the symptom complexes of known diseases,
particularly in developing countries, are likely to be first
considered as of infectious origin or to be the result of
malnutrition (Anon., 1984). The Afghan outbreak of veno-occlusive
disease was considered to be a water-borne infection, until the
chemical etiology was discovered through recognition of a plant
growing among the staple food crop of wheat. The chemicals
responsible for the disease were the pyrrolizidine alkaloids in the
seeds of the plant, which were mixed with the grain (Tandon &
Tandon, 1975).
Generally speaking, there are no sets of clinical
characteristics of diseases that, alone, could lead the
investigator to suspect chemical etiology and exclude other causes.
It is only when the total context of the disease pattern and the
circumstances of its appearance is considered that such an etiology
might be suspected, though some clues may emerge, even from the
initial epidemiological characteristics.
The epidemiological characteristics of diseases of unknown
etiology may vary in the following ways:
(a) A sudden outbreak of a disease that is considered "new" is
often attributed to an unknown infectious agent. The
search for the etiology should take into account factors
of a chemical nature. An evaluation of the
epidemiological pattern of the disease might provide
useful orientations that can be fruitfully pursued. For
example, the outbreak of liver disease in India, which was
later confirmed to be due to aflatoxin exposure (Tandon et
al., 1977, 1978a), was initially considered to be one of
infectious hepatitis, because the dominant features of the
disease were jaundice and other systemic symptoms that
suggested hepatocellular failure. The initial
epidemiological characteristics of the disease indicated
that transmission of the virus was highly unlikely to be a
causal factor, and this prompted the search for another
environmental factor.
(b) Endemic diseases continuously occur and recur in defined
geographical areas. Although such diseases constitute a
chronic health problem that could be studied by
conventional epidemiological methods, many endemic
diseases have an environmental etiology of unknown nature.
For example, according to the recent estimates, Kashin-
Beck disease has affected about 2 million individuals in
certain endemic regions of China, but the specific
chemical etiology has so far escaped discovery (Appendix
III).
When the exposure is not sufficient to result in the
clustering of cases, the disease may remain unnoticed or
unknown.
(c) Some commonly occurring diseases may include exposure to
chemicals as a risk factor. However, the role of
widespread, long-term, low-level complex exposure in the
multifactorial etiology of such diseases is more difficult
to establish and this problem is not addressed in this
publication.
In searching for an etiology, it is important to recognize the
source of the chemical. Diseases that have been identified as
chemically induced, have been associated with various chemicals
with the following origins:
(a) Naturally-occurring inorganic chemicals
There are many naturally-occurring inorganic chemicals that
have been found to be toxic for man, e.g., mercury, lead, and
cadmium. Although these chemicals are neither created nor
destroyed by man, geochemical conditions, natural processes, such
as accumulation in certain biota, and industrial activities may
result in their widespread but uneven distribution, or in the
formation of new compounds that may be more or less toxic than the
naturally-occurring forms.
Diseases can also be caused by excessive exposure to inorganic
chemicals that may be beneficial or even be a metabolic requirement
at low levels. A relationship has been established between
skeletal fluorosis and the long-term elevated intake of fluoride
(WHO, 1984a).
(b) Chemicals of plant origin
Several episodes of disease have been reported resulting from
the accidental contamination of food crops by certain weeds and
their seeds. Thus, contamination of staple food crops with
pyrrolizidine alkaloid-containing seeds has caused large-scale
outbreaks of veno-occlusive disease in Afghanistan (Tandon &
Tandon, 1975; Mohabbat et al., 1976) and the USSR (Dubrovinski,
1952). Furthermore, veno-occlusive disease may also result from
the use of pyrrolizidine alkaloid-containing herbs as traditional
home remedies, as seen in the West Indies (Stuart & Bras, 1955) and
elsewhere (Huxtable, 1980; Ridker et al., 1985).
Staple food sometimes contains toxic substances that are
removed during food processing or do not represent a hazard for
human health under normal circumstances. However, as seen in
Mozambique, modifications in plant constituents induced by
environmental changes, together with changes in methods of food
preparation, and patterns of consumption, can lead to acute or
subacute poisoning. An outbreak of spastic paraparesis in
Mozambique was shown to be related to cyanide intoxication caused
by cassava. During a severe drought, the cyanide content of the
cassava increased naturally. Moreover, famine forced most families
to turn to bitter cassava, which has a higher cyanide content, and
to eat it after drying it for a few days only, whereas several
weeks are required for proper detoxication (Mozambique Ministry of
Health, 1984).
(c) Microbial toxins (chemicals produced by microscopic fungi,
algae, and bacteria)
Exposure to toxins from fungi (mycotoxins) takes place mainly
through the ingestion of contaminated foods, though airborne
exposure to fungal spores containing mycotoxins is also possible
(WHO, 1979b). Contamination of foods of plant origin takes place
generally in the post-harvest period through invasion by moulds.
It is difficult to detect by conventional food inspection practices
because of the microscopic appearance of the fungi. An example of
mycotoxin-associated disease is the toxic effects caused by
aflatoxins in food grains (WHO, 1979b). Exposure to algal toxins
is generally caused through the ingestion of fish and shellfish
that have been feeding on toxic microscopic algae (plankton) and
thereby retaining part of the algal toxins, without actually
showing any organoleptic changes. Examples of such diseases are
paralytic shellfish poisoning caused by saxitoxin and derivatives,
and diarrhoeic shellfish poisoning caused by okadaic acid and
derivatives (WHO, 1984b). Diseases induced by bacterial toxins are
caused by inadequate food processing, during which the toxin-
producing bacteria may infect foods and produce toxins, just prior
to consumption. For example, staphylococcal food poisoning is
caused by enterotoxins from Staphylococcus aureus, and botulism,
by neurotoxins from Clostridium botulinum growing in processed
meat, fish, and vegetables.
(d) Man-made chemicals
A number of acute outbreaks and incidents of illness have been
found to be caused by exposure to pesticides, fertilizers,
germicides, or industrial chemicals. Some of these episodes have
been explained as outbreaks of acute poisoning caused by the
accidental contamination of food, for example by parathion (Diggory
et al., 1977), or of items of household and personal use, such as
baby powder, by hexachlorophene (Martin-Bouyer et al., 1982), and
laundry rinses, by pentachlorophenol (Robson et al., 1969).
Although only short-term exposure may have occurred, health effects
may be permanent, or recovery may be very slow as in the Yusho
episode in Japan where the deceased people had ingested a mixture
of polychlorinated biphenyls, dibenzofurans, and quarterphenyls
(Kuratsune et al., 1969) or in Turkey where liver disease and
porphyria cutanea tarda resulted from contamination of grain with
hexachlorobenzene.
3. GENERAL APPROACHES IN THE INVESTIGATION OF DISEASES OF SUSPECTED
CHEMICAL ETIOLOGY
The nature and magnitude of the problem, as well as the
facilities available for investigating diseases possibly caused by
chemicals, vary from country to country for a number of reasons
including the extent to which the health services have been
developed, and whether stray cases or outbreaks of toxic disease
are being studied. Countries with well-developed infrastructures
in the health services usually have rigid control systems with
regard to food quality, sanitation, and water supplies, and good
investigative facilities. Reasonably good health-care facilities
are available, even in outlying areas. If outbreaks of chemically-
induced diseases occur, they are usually the result of a short-term
exposure to a toxic chemical, affecting a limited number of cases,
which are likely to be noticed as soon as they appear. Thus,
expeditious steps can be taken for their investigation or control.
Investigation and control of outbreaks in countries with
inadequately developed health services need a different approach,
though the principles may be the same.
In this publication, a strategy is discussed, which might be
used in the investigation of episodic or endemic diseases of
suspected chemical etiology. Instead of asking what are the
effects of a specific chemical, the question can be reversed to ask
which chemicals might cause a particular health effect. It may be
difficult to distinguish a chemically-induced from an infectious
disease and to identify the etiological chemical agent. Clues are
often elusive and inextricably mixed with day-to-day occurrences or
the "not-so-unusual" disease phenomena affecting a population. The
search for an etiology often necessitates sequential planning for a
progressive build up of clues.
The identification of the chemical causes of a disease involves
a group of interrelated disciplines, in particular pathology,
epidemiology, and laboratory medicine and toxicology. The approach
may be a straightforward process when a large group of people is
exposed to a chemical with known toxicity, but this may not always
be the case. The search for an etiology will depend on
scientifically clear evidence of linkages between exposure to a
chemical, the biological effects, and subjective clinical symptoms.
Appendix II includes a description of a conceptual framework of
studies on outbreaks (episodes), which resulted in the successful
identification of their chemical etiology and, through this, their
control and prevention. However, it should be said at the outset
that it is not a blueprint for action, but an example that could be
suitably modified as the situation demands. It was designed to
investigate the causes of diseases in which chemicals in the
environment were the principal, rather than a minor, contributory
factor.
Appendix III includes a summary report on the present state of
research concerning the etiology of a wide-spread endemic disease
in which exposure to certain environmental chemicals is considered
an important etiological factor.
In the following sections, the approaches that should be
considered simultaneously, when the chemical etiology of a disease
is being investigated, are discussed at some length.
4. DISEASE APPROACH: RECOGNITION AND DESCRIPTION OF A HEALTH PROBLEM
4.1. General Background
To investigate the etiology of outbreaks of diseases caused by
chemicals, the "disease approach" is the first step in the
methodological framework. Epidemiological and toxicological
approaches are then developed as analytical tools to generate valid
etiological hypotheses and to test them at each stage of the
investigation. The steps or phases recommended are intended to be
progressive and the decision to terminate or modify the process
might be considered at any phase, if appropriate.
In order to investigate outbreaks of disease, or the endemicity
of a disease, it is important to be familiar with the general
disease patterns in a specific geographical area. The incidence
and types of diseases may vary, to some extent, in different
countries and may change with socioeconomic conditions and
industrial activity. However, awareness of the epidemiological
pattern in a given population will make it possible to recognize
changes in disease patterns, the occurrence of new diseases, the
sudden outbreak of epidemics of infectious diseases, outbreaks of
poisoning, or the presence of endemic diseases in localized
geographical areas. The recognition of such diseases is usually
based on observations of health personnel that the frequency of a
common disease has increased, that a hitherto unknown constellation
of clinical manifestations has been encountered, or that the age-
specific incidence of a disease is shifting. When such
observations are reported, they must be critically evaluated to
determine whether these observations are truly abnormal. For
example, it is possible that a physician with a special interest in
certain diseases may simply recognize them more frequently, or that
diseases of different etiological factors may be erroneously
grouped together.
The methodology of epidemiology as described in a recent
publication (WHO, 1983) outlines choices of study design, methods
for the assessment of exposure, and signs and symptoms for the
ascertainment of health effects. However, the precise etiology of
the condition under study cannot be established from the resulting
association alone. In addition, there may be lack of information
on exposure, evidence of combined toxic exposures, or, perhaps most
important of all, lack of proof or evidence supporting hypotheses
linking exposure to specific environmental factors with the
disease. Several disciplines must be involved in providing precise
identification of etiological factors.
Disease investigation begins with awareness of an apparent and
unusual number or cluster of cases with a clinically characterized
disease entity (index cases as discussed below). Therefore, the
initial investigations must almost always involve some level of
epidemiological investigation. An unusual clinical phenomenon in a
population may:
(a) be characterized by pathognomonic signs that do not occur
in a disease of known etiology;
(b) be associated with combination of non-specific clinical
features, signs, symptoms, and laboratory and other data
that do not fit into a known disease category;
(c) constitute a cluster of cases of a disease that normally
occurs with a low frequency; or
(d) constitute an endemic disease of unknown etiology.
After ascertaining that there is an unusual clinical phenomenon
in the population, the search for a chemical etiology and
subsequent action can proceed in the following phases:
(a) descriptive phase, in which the disorder is characterized
by clinical, pathological, and epidemiological features;
(b) hypothesis-generation phase, in which a hypothesis is
assumed concerning the possible etiological factors, on
the basis of clues obtained from the initial studies;
further supportive clues are searched for;
(c) hypothesis-testing phase, in which the clues obtained are
tested by the identification of biological markers of
exposure or injury, detailed pathological studies on
diseased tissues in man and affected animals, and
toxicological studies on animals;
(d) follow-up evaluation, in which follow-up action is taken,
if the causative agent is successfully identified.
These steps are outlined in the Appendix II.
4.2. Recognition of Index Cases
Index cases refer to the first reported case or cluster of
cases of the disease under study. It may happen that the first
reported case is not the first one to occur, and that the true
index case has remained unnoticed. A retrospective analysis of all
available information should always attempt to trace the disorder
backwards to the true index case. In the rural areas of some
developing countries, these cases may be identified by paramedical
personnel or practitioners of traditional medicine. In urban
areas, they may initially come to the attention of the emergency
medical services, or, in the industrial sphere, be identified by
occupational medicine specialists. In order to reduce, or possibly
exclude, distractors from among the cases included in the affected
category, it is essential to define the characteristics of such
index cases. Typically, the index cases exhibit severe forms of
the disease with overt clinical manifestations. At this stage, the
whole range of signs and symptoms associated with the disease may
not be recognized, and index cases should later be thoroughly
evaluated and a general case definition developed.
Once it is presumed that a normally occurring illness is
suddenly occurring at a higher frequency (or has reached epidemic
proportions), or that there is an outbreak of a disease that has
not been observed previously, it must be established whether a true
outbreak exists. For instance, it is possible that certain
conditions in the general population may be overlooked, until
special interest develops or appropriate diagnostic methods are
introduced, with the result that suddenly such conditions are
reported more frequently. This increase merely represents a
reporting artifact and not a true increase. Furthermore, a variety
of diseases may be thought to represent the same condition and the
increase in this condition is again merely a reporting artifact.
After having defined the diagnostic criteria on the basis of
identified index cases, a search should be carried out to identify
all suspect cases. The principles of epidemiological studies are
described in detail in a previous publication (WHO, 1983). Disease
characterization can be carried out by a sequential approach.
Initial screening of the population aimed at identifying all cases
suspected of being involved in the outbreak is followed by phases
in which the disease becomes progressively more clearly defined as
more specific clinical and laboratory criteria are applied. As an
example, in the investigation of the aflatoxin outbreak in India
(Tandon et al., 1977), all cases of jaundice associated with
hepatomegaly and other systemic symptoms were included in the
primary screening. When liver biopsies were taken, features
characteristic of acute infectious hepatitis were seen in
occasional cases, and these were excluded at the stage of case
definition, described in section 4.4.
4.3. Screening of Populations for Suspected Cases
After the index cases have been evaluated, a decision may be
made to screen the affected community. This decision is not
automatic and must be based on an assessment, by appropriately
trained medical and public health personnel, that an outbreak of
the disease has occurred and may be more widely distributed than
appears from the index cases. The aim of screening the population
is to estimate the total incidence or prevalence of a set of signs
and symptoms considered to suggest a disease related to the
suspected etiology. Such screening in developing countries is
frequently carried out by paramedical personnel. Accordingly, the
tests need to be easy to use, e.g., standard questionnaires based
on information obtained from the index cases. An example would
include simple tests of motor coordination to evaluate nervous
system changes, without the use of specialized medical equipment.
Personal history should include age, sex, occupation, life-style
variables, and place and duration of residence. In addition, past
medical history should include relevant data on previous and
current diseases, pregnancy, and lactation.
The number of persons to be included in the initial screening
depends on the specific circumstances of the outbreak. Clearly,
the key limiting factors are economic resources and available
personnel. The efficacy of the screening will be improved by
eliciting the full cooperation of the persons potentially affected
by the disease. The benefits for the population of participating
in the primary screening should be emphasized. Support from the
affected person's family and, for example, the village or tribal
heads, is helpful in conducting primary screening. In more
urbanized areas, the support of community groups or factory
workers' organizations could be beneficial.
4.4. Case Definition
At this stage of the investigation, identification of different
stages of the disease becomes possible. Cases range from those
with the most severe symptoms to those with only subclinical
effects. The case definition should not be so restrictive that
only the "tip of the iceberg" is identified. It should be specific
enough to separate the disease of concern from diseases of other
origin. Ideally, one sign or symptom would be pathognomonic of the
disease under investigation. However, this is rarely the case.
Generally, a number of signs and symptoms and the pattern of their
appearance are used to identify the disease. Individually, these
signs and symptoms would not be either sensitive or specific.
However, the clustering and relative severity of these signs and
symptoms greatly increase their use in identifying cases of the
disease.
Procedures used in case definition are generally much more
reliable and complex, and involve laboratory support and techniques
not applicable in the initial screening. This part of the study
requires more highly trained personnel than the initial screening.
The criteria are based on the most severe cases at the initial
stages and must therefore be considered provisional, since they
will not include mild disorders and subclinical effects. The case
definition should include:
(a) Identification of the target organ or organs and the
characteristic effects. It is critical to recognize that
organ systems have limited types of response and that
these are rarely pathognomonic for a disease caused by a
particular chemical.
(b) Identification of specific groups that appear to be
particularly vulnerable, e.g., infants, or persons living
within a certain radius of a chemical industry.
A description of the clinical appearance of the disease should
include the signs and symptoms, clinical course of the disease, and
pathological findings. Pathological study of diseased human or
animal tissues, early in the outbreak, might provide useful
etiological clues. If autopsies are not available, biopsies from
patients or autopsies of affected domestic animals, as mentioned in
section 4, should be carried out. More detailed information should
be gathered concerning the extent of the problem, i.e., precise
figures on morbidity and mortality rates and time sequence.
Analysis of the demographic data obtained during screening will
indicate whether or not there is a subpopulation at high risk,
e.g., residents in a given area, an occupational group, young
children, or persons with pre-existing problems. The spectrum of
clinical severity may differ among groups of individuals affected
by toxic chemicals to a greater extent than that among patients
with an infectious disease. The wide variation in involvement may
be due to differences in the levels and lengths of exposure and
differences in host susceptibility, because of differences in age,
nutritional status, etc., which should be specified in detail
during the process of identification.
At this phase in the study, it is desirable to review
toxicological information on the potential health effects of the
toxic chemical suspected of playing a role in the etiology of the
disease (section 6). Comparison may identify clinical or
biochemical effects that have not been previously investigated and
may provide a basis for confirming the relationship between the
toxic agent, the case definition, and observed effects. Finally,
toxicological studies may provide predictive information regarding
prognosis, including the progression or reversibility of the health
effects observed.
Because the background prevalence of signs and symptoms in the
general population is not known, it is appropriate at this stage to
survey all persons who appear to be affected by the disease. The
inclusion of a comparison group is essential, in order to identify
a tentatively discriminating factor.
4.5. Case Identification
The definition of the clinical entity, based on rigid quality
control, high specificity and sensitivity, results in the
identification of:
(a) early symptoms that may not have been recognized during
the initial screening;
(b) associated clinical pathological/radiological features of
the disease;
(c) characteristic pathological features in the affected
tissues; and
(d) complications beyond the acute phase, and sequelae.
In this phase of the analysis, the population is screened again
to identify borderline, subclinical, or latent cases using
established diagnostic criteria and specific biological markers.
This may also give a more precise idea about the magnitude of the
outbreak.
4.6. Importance of Pathological Studies
The pathological study of biopsy or autopsy specimens may
provide the crucial clue(s) in the identification of the etiology
of a disease. The proper conduct of pathological studies may
contribute to the formulation of hypotheses regarding etiology, and
influence the selection of subsequent studies. Morphological
changes in the principal target organ may prove to be pathognomonic
of the etiological agent. In the investigation of an outbreak of a
disease in India, the presence of syncitial giant cells in human
liver tissue and recognition of the fact that an identical lesion
had been previously observed in the liver of rhesus monkeys exposed
to aflatoxins, suggested the etiological role of aflatoxins in this
human disease outbreak (Tandon et al., 1977, 1978a). The
morphological changes observed may also help to exclude infectious
disease as a cause of the illness.
For various reasons, there may be difficulties in obtaining
human autopsy material. In such an event, biopsy of the diseased
organ or examination of autopsy material from field animals
suffering from a disease identical to that in man may prove useful,
as again happened in the aflatoxicosis outbreak (Tandon et al.,
1978a). The biopsy could be carried out as part of a diagnostic or
therapeutic procedure for the benefit of the patient, for example a
liver or a kidney biopsy could be carried out following
paracentesis, or the bony tissue, resected as a part of corrective
surgery, could be examined. Histological appearance may identify
the specific target tissue and the affected cell type or could
decisively indicate infection or some other specific disease.
Descriptions should be in the internationally recognized standard
medical nomenclature.
The usefulness of pathology specimens may be enhanced by
providing advice and materials for proper tissue fixation, and
storage instructions. Parallel sampling for chemical analysis
should always be considered and such specimens should be stored by
freezing and without fixation.
4.7. Reporting Systems and Case Records
In most countries, reporting systems exist for recording
infectious diseases. A similar approach would be useful for the
reporting of outbreaks and epidemics of diseases of unknown origin.
Delays in notifying central health authorities may occur for
many reasons. If different patients are treated by different
physicians, there may be a time lag before a disease outbreak is
recognized. The delays should be avoided, as far as possible, as
prompt and concise reporting is necessary for establishing the
etiology of the disease and controlling the outbreaks. Biological
specimens should be secured, especially from the index cases, and
the time interval between onset of illness and biological sampling
should be noted. Even initial studies might provide useful clues.
Records should be kept of the index cases, if further evaluation or
periodic reexamination of index cases is thought to be warranted,
e.g., for the development of a case registry and long-term,
follow-up studies. Such a registry would allow the investigators
to study the natural history (or progression) of the disease.
Unfortunately, a number of index cases may be lost to follow-up,
when it is not initially recognized that an outbreak is occurring.
On the other hand, development of registries is not always
desirable or cost productive. If long-term follow-up of affected
persons is deemed desirable, certain possible constraints should be
noted.
The following problems are generally faced in the development
of a case registry:
(a) high costs and lack of financial support;
(b) cases of chemical toxicity are generally not reportable;
(c) lack of suitably trained medical and paramedical
personnel, capable of maintaining a registry;
(d) mobility of populations;
(e) lack of cooperation of health personnel;
(f) inconsistency of disease nomenclature.
The problems encountered in recognizing and recording diseases
of chemical etiology are illustrated by the historical evidence on
lead poisoning (Grandjean, 1975; Mahaffey, 1985). The failure to
recognize lead exposure as a cause of the disease was due to: (a)
failure to appreciate the importance of individual susceptibility;
(b) unsuspected sources of exposure; (c) non-specific pathological
changes; and (d) classification into several ill-defined clinical
syndromes. With the occurrence of ubiquitous lead pollution, there
may be other insidious health effects caused by past or long-term
exposure, which may be difficult to identify or recognize.
5. EPIDEMIOLOGICAL APPROACHES: SEARCH FOR DETERMINANTSa
5.1. General Background
One of the important steps, when searching for the etiology of
diseases, is to establish and validate associations between the
occurrence of the disease and exposure to one or more common
factors that could be considered as determinantsa. The classical
epidemiological approach is to generate a hypothesis from
preliminary information collected through descriptive study and
then test it in an analytical epidemiological study of appropriate
design, as described in detail by WHO (1983). Although this
sequence is logical, the exploration of the chemical etiology of a
disease may not necessarily follow this sequence, particularly when
an acute outbreak of disease occurs. In such situations, rapid
recognition and resolution of the problem is of the utmost
importance. Although a series of steps is outlined below, in
practice, they will often have to be carried out almost
simultaneously.
The early recognition of an outbreak of, or unusual increase
in, disease depends on careful observation of cases and a reliable
reporting network. Expeditious investigation of the
outbreak/occurrence of cases cannot be overemphasized. The
investigator should obtain as much information as possible, such as
the geographical extent of the outbreak, the population at risk,
the number of cases, distribution of cases in the population,
clinical manifestations, time of onset of the outbreak, and whether
similar outbreaks have occurred in the past. This preliminary
information will enable the investigator to develop the tentative
hypotheses necessary to decide on the technical support systems
needed. Additional advice can be obtained from the pertinent
scientific literature and from international agencies and other
institutions in relation to the nature of samples that should be
collected, and the names and addresses of specialized laboratories
for the analysis/identification of toxic materials and biological
fluids/tissues from diseased animals and patients.
5.2. Collection of Information and Criteria for Obtaining Specimens
The availability of properly trained and briefed personnel is
an essential element in the conduct of a study. The investigating
team will have to obtain detailed data on the disease
characteristics and must include adequately trained clinical staff.
The help and cooperation of international agencies and other
departments within the country, or in other countries, may be
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a A determinant is any factor, whether event, characteristic, or
other definable entity, that brings about change in a health
condition, or other defined characteristic (Last, ed., 1983).
The same source recognizes predisposing factors (e.g., age, sex,
occupation), enabling factors (e.g., climate, income),
precipitating factors (e.g., exposure to noxious agents), and
reinforcing factors (e.g., repeated exposures) in causation of
disease.
needed, but the investigating team should comprise local
investigators, as a cultural and language identity with the
populations being investigated is essential. When possible, the
laboratory worker who will analyse the samples should participate,
otherwise this team should receive adequate briefing from the
responsible laboratory regarding the type and amount of samples to
be collected, method of storage, transport, etc. In particular, a
statistician should be consulted regarding the size of population
to be studied, when dealing with epidemiological studies of chronic
diseases. In the absence of ideally trained personnel in the
investigating team, efforts should be made to brief and train
available people appropriately.
A wide range of specific information should be collected in
order to identify, as far as possible, all the relevant factors
common to the identified cases. Examples of such factors are given
in Table 1. Another possibility could be the use of the
classification proposed by Last (1983) with an identification of
the predisposing, enabling, precipitating, and reinforcing factors.
However, situations will differ, and some of the items listed may
not apply in certain situations.
Table 1. Factors to be considered during an epidemiological
investigation of an unknown disease
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(a) Factors relating to the physical environment
Geographical location, including altitude, nature of terrain,
distance to rivers, lakes, swamps
Climatic conditions
Seasonal occurrence of symptoms
(b) Man-made environmental factors
Diet
Food preparation, cooking, and eating habits; storage
practices
Water supply, sanitation
Agricultural practices, including the use of fertilizers and
pesticides
Industrial environment, including mining
(c) Factors relating to the affected subjects
Age distribution
Sex distribution
Family aggregation of cases and family structure
Social and cultural factors: ethnic groups, religion,
education, etc.
Occupation
Socio-economic status, including income level
Mobility of the population, migration
Duration of residence in the area
-------------------------------------------------------------------
Note: Recent changes concerning any of these factors should be
carefully documented.
Background information on general health statistics should be
collected through government/municipal/county/hospital/primary
health centres, together with the following items: morbidity,
mortality, case fatality rates, and the trends in these indicators.
Special attention should be paid to the possible occurrence in the
past, or in nearby areas, of similar outbreaks, or even sporadic
cases, constituting the unusual clinical entity.
Information on the environment must include recent changes in
the environment if any, such as the destruction of forests,
building of dams, opening of new industries, discharge of
effluents, new range of products, or change in manufacturing
processes. The agro-ecological factors include the introduction of
new varieties of food grain, mechanization of agriculture, use of
agrochemicals, storage practices of harvested food, changes in the
cultivation pattern, etc.
A co-existence between a disease in human beings and a similar
disease in animal species provided important clues in some of the
earlier studies of diseases later identified as being caused by
exposure to chemicals in the environment. Examples of these
studies are those on Minamata disease (WHO, 1977), veno-occlusive
disease (Tandon & Tandon, 1975; Tandon et al., 1976), and the
aflatoxin outbreak in India (Tandon et al., 1977, 1978a).
Information from farmers or veterinary officials on the outbreak or
occurrence of related diseases in farm and domestic animals or
other fauna and flora may yield valuable data.
Various additional sources can be used in the collection of
relevant information. The most useful information would generally
come from the members of the affected community themselves.
Further sources of information include community elders, social
workers, and health personnel, including primary health and
paramedical workers, general practitioners, and practitioners of
traditional medicine. Attention must also be paid to additional
factors. Thus, a family member or a member of the affected
community may have very specific useful information such as
practices in food storage or the special use of pesticides. Some
data could be collected through formal questionnaires for the
village (unit) level, family level, or individual level. Other
methods could include less-structured personal interviews. Some
useful information may already be recorded elsewhere, for instance
demographic characteristics.
An intensive or extensive sampling strategy should be designed,
depending on a balanced trade-off between what would be desirable
and what is feasible. The specimens to be sampled should include
biological samples, as well as samples of food, air, water, and
other commodities. In the absence of precise knowledge of the
possible etiological factor and particular source, a large number
of samples covering a wide range should be collected, the sample
size being adequate for a reasonable range of analyses. The range
of sampling to be carried out should be decided on after generating
a tentative hypothesis on the possible etiological factors, based
on previously collected information. However, even if a precise
hypothesis has not been defined, potentially useful samples must be
obtained as early as possible. The samples should preferably be
representative of the index cases, and sampling could be restricted
to the families or individuals with the most typical case history.
The samples should be obtained from both affected and non-affected
areas.
For practical purposes, there are limitations to the number of
samples that can be collected and processed. For this reason, some
judgement must be made as to what would represent the most useful
samples. Such decisions are influenced by the time that has
elapsed between the onset of the illness and the beginning of the
investigation, the pertinence of the samples, and the possible
routes of exposure. For instance, if a food commodity is suspected
in acute outbreaks, the food that was consumed immediately prior to
onset of illness would represent the most valuable samples.
Collection of the cooked food actually consumed is emphasized.
Samples can also be collected from the food grains and the cooking
medium from both local and commercial stores. Identifying
pertinent exposure to environmental sources may be more difficult
in the case of chronic illnesses, as such exposures may have
occurred some time in the past or may have varied over time.
There is a danger that samples might be contaminated,
destroyed, or damaged during storage or transit. Biological
samples should be properly preserved in formalin or in an insulated
container with ice or dry ice. Agricultural commodities should be
adequately dried before transporting. These requirements must be
agreed on with the analytical laboratory.
5.3. In-Depth Study of Cases
The result of the initial investigation is the identification
of one or several factors that are common to all identified cases
of the disease or seem to be related to its distribution in the
community. An in-depth study of the outbreak/occurrence of cases
requires that population-based studies, aimed at identifying the
determinants of the disease, should be complemented with case-
control studies. In the case-control design, cases of the disease
are matched to a similar number of controls (people with no
symptoms of the disease), in order to test the strength of the
association between the exposure to the suspected etiological
conditions and the occurrence of the disease. The relative risk
associated with exposure can be calculated on the basis of such
studies (section 5.4).
Once the situation has been evaluated in the field, a special
subgroup of the diseased population can be selected, unless only a
small group of people have been affected, and studied in depth
as a supplement to more formal epidemiologically designed
investigations. Such studies include detailed background
questionnaires, medical examination, and relevant laboratory tests.
The type of information to be collected will depend on the
situation. It is important to be as concise as possible and not to
obtain a great deal of extraneous information, as this will only
impede analysis of the data (see also sections 5.2 and 6).
The selection of cases for detailed investigation will depend
greatly on the specific factors involved in the particular
outbreak. The following factors deserve consideration. The most
typical cases should be included. If more than one member of a
family is affected and a common factor among families is sought,
then it may suffice to examine only one member per family.
However, if the family is to be characterized, all members of the
family should be examined. It might be useful to confine the
examination to children or other specific segments of the
population. In other situations, a common factor might be sought
in individuals belonging to diverse subpopulations. Cases that
suddenly develop in another geographical area may be useful in
identifying a common factor. Alternatively, random sampling can be
used to obtain representative samples for the epidemiological
studies.
Having dealt with the more readily available information in an
acute outbreak of disease, additional studies should then be
contemplated, such as more detailed morphological examination of
affected target organs, and chemical analysis of biological fluids
and tissue samples. In addition to the fixation of tissues for
morphological studies, selected tissues and biological fluids
should be frozen for possible chemical analysis, only after
obtaining initial clues suggesting a possible toxic agent. For the
successful identification of an etiological agent, it is important
that the potential source of the toxic agent is identified and the
exposure established through analysis of the incriminating
material, such as food, or of body tissues and fluids. The samples
of such tissues and fluids, as well as of the incriminating
material have to be properly collected and preserved following the
advice of the analytical laboratory. In the absence of specific
information to the contrary, freezing at the lowest possible
temperature is the best method of preservation. Individual samples
should be identified and stored separately, and pooling or mixing
of samples should be avoided. However, discretion in using this
approach is advised, since extensive analysis is laborious and will
rapidly deplete the supply of available samples.
5.4. Evaluation of Epidemiological Data
The data collected must be analysed for the existence of dose-
response and dose-effect relationships and for the occurrence of
specific differences between affected and comparable unaffected
individuals. Although results obtained should preferably be
representative for the population examined, it may not be possible
to meet this criterion very rigidly in studies of acute outbreaks.
Appropriate reservations as to the general validity of such results
must then be made. In some outbreaks of acute poisoning, the
illness experienced and the development of the epidemic may be so
specific that it may not be feasible or necessary to apply a
statistical approach. A statistically significant result may only
indicate a "spurious" association occurring by chance, and a non-
significant association could be due to an insufficient number of
observations, lack of precision in the measurements performed, and
other factors.
The information obtained must be carefully scrutinized for the
presence of bias. For example, bias in selection may be of
importance if only the most severely affected patients are examined
and differ in some important aspects from the group of patients as
a whole. Ascertainment bias may occur if a local informant is
particularly aware of, and reports, cases. Reporting bias in
information may occur if prior information about the disease in the
news media influences answers to questionnaires. Errors may occur
in many situations, if samples are mislabelled or if artifacts are
introduced. Confounding is likely to pose a problem, especially in
studies of multifactorial diseases.
Epidemiological data can be analysed using the case-control
approach and the follow-up approach (WHO, 1983). In both
approaches, control groups need to be selected. In the first
approach, the controls are people without signs and symptoms of the
disease; in the other approach, the controls are those who have not
been exposed to the chemical suspected of causing the disease.
In the study of acute outbreaks of unknown etiology, it is
usually not feasible to select proper control groups, as the
healthy people in the affected area may also be exposed, but to a
lesser extent, and usually the causative agent has not been
identified at this stage. The usual procedure is to select as a
comparison group, people who do not present signs and symptoms
characteristic of the disease, or who appear not to have been
exposed to the suspected agent. In fact, these comparison groups
are never fully comparable to the group under study and it should
be emphasized that the absence of valid comparison groups may
severely hamper the value of the study. Although, during
outbreaks, it may not be possible to identify valid comparison
groups, tentative conclusions must be drawn on the basis of a
critical assessment of all available data by the observer. On the
other hand, when dealing with endemic disease, it should be
possible to select proper comparison groups controlled for specific
suspected determinants on a prospective basis.
6. TOXICOLOGICAL APPROACHES: STUDIES ON CHEMICALS POSSIBLY INVOLVED
6.1. Experimental Animal Studies
Animal studies are being used to complement investigations of
outbreaks of disease and of endemic diseases of suspected chemical
etiology. The principal aim of these studies is to assist in the
identification of the toxic substance and also to clarify the
mechanism of action of the substance, after it is identified, and
to develop an animal model for further study of the disease.
When a possible route of entry of the toxic agent is suspected,
the material can be administered to animals by this route to see
whether or not an illness is produced. The animal model developed
should reproduce the pathological features of the disease closely
similar to those in human beings, and attention should be given to
the target organ and types of cells involved (e.g., neurons,
chondrocytes, etc.), the presence of storage materials in tissue or
inclusion bodies, and the types of cellular reaction in the injured
tissues. It may not be possible to reproduce the exact clinical
disease in animals, because the species chosen for study may simply
not react to the toxic agent in exactly the same way as a human
being. Alternative species may be more or less sensitive to the
offending agent, or the target organs may vary in different
species. Therefore, toxicological testing should preferably be
done using a species in which a disease similar to that encountered
in human beings has been observed in the field. At times, it may
not be possible to develop an animal model by simple exposure to
the suspect chemical, since the disorder may be multifactorial, and
simultaneous exposure to other environmental factors may be
necessary to develop a syndrome comparable to the human disease.
Such factors could include: concurrent infectious disease,
nutritional deficiencies, and mixed chemical exposures. For
instance, in encephalitis associated with the oral intake of
bismuth salts, it was impossible to reproduce the disease in any
animal species, in spite of the fact that the role of this compound
in human disease had been established (Martin-Bouyer, 1981).
As mentioned, human beings may be more or less susceptible to
the chemical than animals. Nevertheless, the dose-response
relationship is an essential consideration in the design of an
experimental study. The study should be designed to determine the
minimal toxic dose, whether the toxic chemical may be accumulated,
and if there is a time lag between the exposure and the effect.
For instance, in the methylmercury outbreak in Iraq, loaves of
bread containing the toxic substance were fed to domestic animals,
but time was not allowed for the toxic effects to become manifest
(latency period), resulting in the false interpretation that the
bread was not toxic (Bakir et al., 1973; WHO, 1977). Also, if the
material fed to animals is a foodstuff, it must be ascertained that
a caloric or nutritional imbalance or deficiency is not produced,
resulting in disease symptoms not related to the toxic material.
Animal studies can provide information on the development of
characteristic pathological changes produced in the affected organs
by the chemical suspected of being involved in the etiology of the
disease. They can also help to identify factors influencing
susceptibility to this compound. When the possibility cannot be
excluded that the etiology concerns exposure to a complex mixture,
or is otherwise multifactorial, it would be misleading to base the
evaluation only on the results of tests for the effects of exposure
to a single compound.
Studies on biochemical effects should be designed and
interpreted with cautious consideration of other measures of
toxicity. Studies of the metabolism and toxicokinetics of a
putative chemical agent in animal models can provide information,
important for planning and for the interpretation of results of
screening and of analysis of biological specimens for toxic
substances and their metabolites. Such information includes
identification of metabolites, determination of excretory rates,
and elimination half-times of the chemical agent and its
metabolites. Principles of toxicological investigations and
toxicokinetic studies are dealt with in detail in previous EHC
documents.
6.2. Analysis for Toxic Substances
Analytical chemistry is important in investigations of endemic
disease or of acute and chronic poisoning episodes in order to
identify and quantify the toxic chemical within the environment and
in affected persons. It is desirable to quantify the offending
agent in tissue samples to identify and, if possible, quantify, new
exposure and to determine a dose-response relationship. However,
analytical methods with appropriate sensitivity and precision may
not be accessible within the area of disease outbreak.
Furthermore, some chemicals are rapidly metabolized and excreted
making their detection in body fluids and tissue samples difficult,
or even impossible. Thus, the time between exposure and the
collection of human specimens may be crucial, not only for the
detection of the responsible chemical(s) and metabolites, but also
for estimating the dose associated with the observed effects.
Analysis for microbial toxins represents a special problem.
Intoxications caused by microbial toxins are mainly foodborne, but
respiratory exposure has also been known in the case of fungal and
algal toxins. Microbiological investigation of suspected foods can
be an important step in the identification of the chemical
involved, indicating the chemical method of analysis to be applied
for unequivocal identification of the causative agent. Thus, if
Staphylococcus aureus is the predominant member of the microflora
in foods that have been associated with an acute gastrointestinal
disorder, then the food should be analysed for Staphylococcus
enterotoxins. Identification of Aspergillus flavus growing in
foods (cereals, oil seeds), associated with acute hepatitis, may
suggest analysis for aflatoxin B1, B2, G1, and G2 (WHO, 1979b).
Routine methods are not available for the chemical analysis of some
microbial toxins. Identification and quantification can then be
achieved through bioassays, though the analytical power is
drastically reduced compared with chemical methods. Thus, exposure
conditions during outbreaks of paralytic shellfish poisoning (PSP)
are estimated on the basis of a standardized mouse assay (WHO,
1984b; AOAC, 1980). However, chemical procedures for the
determination of paralytic shellfish poisoning components, such as
high-pressure liquid chromatography, are available and may soon
replace a bioassay.
6.3. Toxic Chemical Information Data Systems
Most data systems are based on studies exploring toxic effects
produced by exposure to known, specific chemicals, plants or their
extracts, natural toxins, etc. In other words, these systems are
developed under circumstances in which the agent is known. When a
disease is the starting point of investigation, the signs and
symptoms are known, but the chemical is unknown or only suspected.
A number of existing data systems listing the toxic effects of
chemicals are computerized. These systems can be used by
professional information specialists to list all chemicals reported
to produce a specific effect, e.g., neurotoxic effects. However,
the process of establishing diagnostic criteria involves knowledge
of the relative specificity of various signs and symptoms as well
as of the order of their appearance. Because of this, relevant
information from such existing systems can be obtained through the
interaction of a professional information specialist with a
specialist of a suitable medical background.
A source would be useful, providing information on specific
requirements for the collection of biological specimens, the types
of specimens to be collected, the amount of sample needed for
chemical analysis, means of preservation of the specimens, as well
as a directory of laboratories performing specialized analyses.
7. PROBLEMS IN ESTABLISHING CHEMICAL ETIOLOGY
7.1. Causation in Human Disease
Human disease occurs as a result of a series of events,
beginning with some initial insult or insults, which then develop
further. The final manifestation of disease may be the result of
various promoting, modulating, or interfering factors related to a
number of factors including genetic make-up, nutrition, life style,
and environment. In some situations, a specific disease simply
seems to develop as a direct result of a particular factor, i.e., a
monocausal relationship. However, frequently, more than one factor
may be involved in the evolution of the disease. Also, several
conditions or characteristics may be associated with the occurrence
of the disease, without necessarily being causally related. Thus,
in the search for the chemical etiology of a human disease,
specific causal factors that constitute necessary (though rarely
sufficient) conditions for the development of the disease need to
be identified. When searching for these causal factors, case
definitions and diagnostic criteria must adequately distinguish the
particular disease under investigation from similar conditions with
different etiologies. However, the disease should not be separated
into too many subentities as this blurs the impression of a common
causation. Individual disease entities frequently have a
heterogeneous etiology, as in the case of end-stage kidney disease
or organic brain dysfunction. Some diseases are called
"idiopathic" or "essential", their causes being unknown, and
eponyms and pathological features are frequently the basis for
names of diseases or their classification. The same chemically-
induced liver disease has even been given different names in
independent outbreaks, viz., "hepatitis with ascites" (Dubrovinski,
1952) and "veno-occlusive liver disease" (Tandon & Tandon, 1975).
It may be difficult to determine whether an outbreak of a disease
is new or, if similar outbreaks have occurred in the past, whether
the etiology has, perhaps, already been elucidated.
In the investigation of disease outbreaks or endemic disease,
the analysis must first of all focus on the clinical and
epidemiological features of the disease. Pathology, toxicology,
and other related disciplines provide further information.
Detailed analysis of the clinical manifestations and morphological
changes in organs may at times help to identify etiological agents
(Parish et al., 1979; Cooper & Kimbrough, 1980). On the other
hand, some chemicals that cause acute poisoning and death may show
few, if any, morphological changes in organs or only very non-
specific changes (Diggory et al., 1977). Several compounds produce
morphological changes that can be considered characteristic, even
if not necessarily specific for one compound, e.g., status
spongiosus of the white matter of the nervous system, which is
observed after exposure to hexachlorophene or triasultane
(Kimbrough, 1976). In the same way, some biochemical alterations
can be considered characteristic, such as the inhibition of
cholinesterase by organophosphorus compounds (Wills, 1972), or the
inhibition of uroporphyrinogen decarboxylase in the liver by
hexachlorobenzene, resulting in acquired porphyria cutanea tarda
(Cam & Nigogosyan, 1963; Taljaard et al., 1971; Felsher et al.,
1982). However, the circumstances of the events leading to the
illness need to be investigated in detail, since the nosographic
specificity may not allow proper judgement without supporting
information.
For many chronic diseases, the situation is more difficult. A
chronic disorder could result from an acute insult, such as the
permanent paralysis caused by triorthocresyl phosphate (Morgan &
Penovich, 1978), or the onset may be insidious resulting from a
cumulative effect following repeated insults, such as the
development of emphysema after years of smoking. Finally, a
disease may have a composite etiology, such as glucose-6-phosphate
dehydrogenase-associated anaemia, which is caused by a combination
of genetic abnormality and an environmental chemical.
An individual disease is recognized by its characteristic
combination of symptoms and signs. Each component may not
necessarily be pathognomonic, but the association between otherwise
non-specific symptoms and signs may constitute a typical
appearance. For example, Thomas Addison, in the 19th century,
first described pernicious anaemia by separating it from general
anaemia, since it occurred without any discoverable cause, such as
loss of blood or malignant disease. In the case of pernicious
anaemia, the absence of other signs present in previously
established forms of anaemia, was a surprising observation.
Subsequently, the discovery of vitamin B12 and the mechanism of its
absorption in the gut was discovered. Research on several other
diseases has followed a similar line.
In approaching the etiology of a "new" disease, a step-wise
series of considerations may be useful, starting from more general
criteria and concluding with a detailed evaluation of the strength
of the accumulated evidence. The initial steps are particularly
useful, when considering strategies to elucidate an outbreak of a
new disease, while the final evaluation of the data is similar to
criteria generally used when considering causal links.
If a disease occurs in a particular environmental setting, this
should be characterized with regard to a set of factors, discussed
in section 5.2 and summarized in Table 1. Genetic disease should
be considered. The following considerations may be useful with
regard to inherited diseases: (a) occurrence of the disease in
definite proportions among persons related by descent; (b) failure
of the disease to appear in unrelated lines (e.g., spouses, in-
laws); (c) characteristic age of onset and course, in the absence
of known precipitating factors; (d) greater concordance of
incidence in monozygotic than in dizygotic twins. Furthermore, a
genetic component may be indicated by studies of genetic isolates
or races, more detailed examination of clustering within families,
relationship to blood types, and occurrence of characteristic
chromosomal anomalies (Murphy, 1972). Many diseases have a genetic
component that may determine individual susceptibility (Kimbrough,
1984). Also, some forms of inherited or inborn disease are not
expressed, unless an individual is exposed to environmental
chemicals or drugs, e.g., with atypical plasma-cholinesterase
(Baker et al., 1977) or deficient glucose-6-phosphate dehydrogenase
(G6PD).
In the case of environmentally-related disease, individuals who
move into the environmental setting run a risk of developing the
disease, while individuals who leave will normally not suffer
further deterioration and may even recover.
If an acute illness of unknown etiology is encountered, both
infectious and chemical causes should be considered. Principal
investigations into the causes of the disease should be governed by
the most likely etiology. However, other possible causes
(infectious versus chemical, versus multi-factorial) should not be
ignored. Koch's postulates, which were developed to elucidate
microbial infections, rarely if ever apply to chemical-induced
disease.
7.2. Consideration of a Chemical Etiology
The distinction between chemical and infectious etiology is of
special importance when considering the possible strategies for
prevention. In this regard, two main sets of data should be
considered, i.e., clinical symptoms and epidemiological
characteristics. In addition, the results of laboratory
investigations and experimental animal studies may further
elucidate the question, if supplementary evidence is needed.
In considering clinical patterns, sudden deaths early in the
outbreak after a prodromal period of a few hours would suggest a
chemical etiology. Non-pathognomonic individual signs and symptoms
taken alone are of little value in distinguishing between poisoning
and infection. Thus, although it is not a common feature of
diseases caused by chemicals, fever may be seen with compounds that
uncouple oxidative phosphorylation, or otherwise impair temperature
regulation. Examples of such compounds are: pentachlorophenol
(Robson et al., 1969), dicoumarol (Toolis et al., 1981),
hexachlorophene (Martin-Bouyer et al., 1982), and aflatoxin (Ngindu
et al., 1982). Sudden enlargement of lymph nodes, increased
peripheral white cell counts, persistent diarrhoea after "cessation
of exposure", and early acute inflammatory exudates are usually not
part of the clinical picture of a chemical poisoning. On the other
hand, in metal fume fever, both fever and increased white cell
counts are seen (Parke, 1982). Thus, the total clinical picture
should be considered. Moreover, chemicals may modulate the
function of the immune system or otherwise increase individual
susceptibility to infection. In this case, infection would be seen
as pre-disposed by chemical exposure.
Consideration of the following epidemiological features may be
helpful when investigating the etiology of a disease not previously
encountered:
(a) case-to-case transmission of the disease (presence or
absence of secondary cases);
(b) common source of exposure;
(c) have all patients received the same dose of the chemical;
(d) geographical distribution of cases within well-defined
areas; and
(e) distribution within particular age groups, sex,
socioeconomic strata, and other demographic subgroups.
Early in an outbreak, it is often difficult to identify
features characteristic of diseases caused by certain chemicals
(e.g., hexachlorophene) or infectious agents (e.g., Legionnaire's
disease). The occurrence of secondary cases within a family, days
to weeks later, might suggest an infectious agent. If such
secondary cases occur within several families at regular intervals,
an infectious agent with an incubation period is suggested.
However, no secondary cases were observed in, for example,
Legionnaire's disease. Therefore, it may not be possible, early in
an outbreak, to determine whether a disease is infectious by nature
or caused by a chemical, and both leads will have to be followed
up. As the epidemic progresses, this distinction is likely to
become easier.
7.3. Temporal Relationships
The temporal relationship between the disease and associated
variables must be known in order to establish a causal
relationship. Thus, the time sequence is an important criterion in
evaluating causality and should be considered early in the process.
Sometimes, specific events can be associated with the onset of
illness, such as the change of a production process in a chemical
factory, or the use of a new chemical in a commercial product, as
in the case investigated by Mallov (1976) of methyl-isobutyl-ketone
which was replaced by methyl- N-butyl ketone. These and similar
leads should be carefully investigated. Though a time-relationship
should be sought, the temporal association between cause and effect
may not be very obvious and may follow an unpredictable pattern.
Exposure to the chemical factor must occur or begin prior to
the development of disease. In the case of acute toxicity, the
adverse effects follow as an obvious consequence of the chemical
exposure. However, this sequence may frequently not be apparent.
This is the case when exposures are long-term, irregular, or mixed.
Some chemicals are rapidly metabolized and excreted, thus
disappearing from the body shortly after exposure. In other cases,
the chemical is accumulated in the body, and may remain in body
depots for decades, perhaps resulting in disease much later than
the initial exposure. This sequence would depend on dose and on
individual susceptibility. Also, when the effect is non-specific,
develops insidiously or is delayed, the time of onset of the
disease may not be well defined. In addition, the expression of
disease may be determined by a factor independent of the chemical
exposure.
A chemical may cause an acute illness from which the patient
appears to recover only to develop a permanent injury after a delay
of several days to weeks, as in the case of neuropathy after
triorthocresyl phosphate intoxication (Morgan & Penovich, 1978) or
the development of cataracts following ingestion of dinitrophenol
(Horner et al., 1985). Continuous internal exposure to, e.g.,
persistent chemicals or asbestos fibres, may ultimately lead to
disease. Certain diseases, such as cancer or lung fibrosis, may
continue to progress, even after the exposure has long ceased.
7.4. Biological Plausibility
While specific chemical etiology may be suggested by the
clinical and epidemiological features, additional leads can be
obtained from detailed examination of autopsy samples and clinical
laboratory data including results of chemical analysis for toxic
substances (section 6.2). Once a chemical or a family of related
chemicals is suspected in an environmentally-induced disease, the
criterion of biological plausibility in establishing the role of
the suspect agents as etiological factors in the disease has to be
considered. This criterion is important when investigating causal
relationships. However, in many cases, the toxicokinetics and/or
biochemical mechanism of toxic action of a particular chemical are
not known with certainty. In such cases, it is more difficult to
use biological plausibility as a criterion to determine the
association between a given disease and a particular chemical
agent. Nevertheless, as toxicological investigations advance, the
linkage of various metabolic effects with specific chemicals
becomes possible and should be pursued. When reviewing the toxic
effects of chemicals, the extent to which the affected population
could have had access to the substances under consideration should
be determined. Furthermore, if a suspect chemical compound is
known to have, for instance, haemolytic effects, and the disease in
question does not involve haemolysis, then this compound can
effectively be ruled out as a causative factor in the disease. On
the other hand, if the suspect agent is known to inhibit or induce
certain metabolic pathways or enzymatic reactions and these
biochemical activities are depressed or activated in the disease
concerned, then this can be taken as supportive evidence for a role
of the chemical in the etiology of the disease.
When the effects of exposure to a chemical, found to be
associated with the disease in question, do not fulfil the
criterion of biological plausibility, the possibility should be
explored of contamination of the chemical with a more toxic
substance. The purity of manufactured chemicals may vary and they
can occasionally contain trace amounts of highly toxic
contaminants. Furthermore, exposures to such mixtures may result
in additive, synergistic, potentiating, or antagonistic effects.
If only exposure to the technical grade or less than pure compound
is identified, it may be difficult to explain the illness observed,
as in the case of Yusho disease, where the clinical manifestations
greatly exceeded the severity expected from polychlorinated
biphenyl exposure alone, but would be explained by the presence of
trace amounts of polychlorinated dibenzofurans (Masuda & Yoshimura,
1984). In such situations, it may therefore be useful to evaluate
the production process of the chemical involved and to determine
the extent to which toxic impurities are present (Baker et al.,
1978).
Toxic impurities may also develop on storage at high
environmental temperatures, or because of exposure to sunlight.
Furthermore, human beings may be exposed simultaneously to more
than one chemical, resulting in possible interactions.
From the examples presented above, it should be clear that both
pathophysiological and biochemical alterations can be used to
establish whether or not the suspect agent satisfies the criterion
of biological plausibility. If the criterion cannot be met at an
early point in the investigations, a re-evaluation should be made,
when more information has been obtained.
7.5. Dose-Response and Dose-Effect Relationships
If possible, the search for, and confirmation of, chemical
etiologies for specific diseases should include studies on
relationships between the incidence and severity of the particular
disease and the intensity and duration of exposure to the factor or
factors suspected of causing the disease. However, a simple
relationship between "dose" and disease outcome may not necessarily
be apparent.
In outbreaks of acute poisoning, the severity of the clinical
manifestations will generally depend on the dose of the chemical.
For instance, food may be contaminated, but the level of
contamination and individual intake may not be uniform. Some
people ingesting much of the food item may receive a high dose and
others a much lower dose. Therefore, some of the exposed may
develop severe disease, while others may only develop a few of the
symptoms and signs related to the disease, or none at all. For
some diseases, a quantal relationship exists where the same type of
exposure will result either in a certain type of disease or in no
obvious ill effects. Different segments of the population may vary
in their susceptibility to toxic effects. Depending on the dose,
the effects may be acute, following one-time inhalation, ingestion,
or dermal exposure to a toxic quantity of a substance. However, at
very low doses, a single dose may not result in any illness,
particularly for chemicals that are cumulative. Thus, the
integrated exposure over a long period, as reflected by the build-
up of the chemical in the body, should be taken into account in
dose-effect, dose-response considerations. Such long-term exposure
levels should be compared to general background levels, and, if
possible, properly selected control areas should be examined as a
reference.
From results in experimental toxicology, it is known that many
chemicals affect cellular and subcellular systems before overt
disease occurs. Some such effects can be quantified using non-
invasive techniques or by analysing a blood samples. The clinical
significance of many of these tests is not clear at the moment, and
they need to be validated further. On the other hand, some of
these tests, for example the determination of red blood cell-
cholinesterase and, within certain risk groups, determination of
urinary-beta-microglobulin excretion, have become useful markers of
chemical exposure, and/or effects, and have been used for dose-
effect and dose-response evaluations.
7.6. Effects of Intervention
There are two types of intervention. Primary intervention
involves efforts to prevent continued exposure to the offending
environmental factor, while secondary intervention prevents or
ameliorates the damage caused by the exposure. Distinguishing
between these two categories may not always be straightforward,
particularly when the pathogenesis of the disease is not known.
However, if adequate prevention can be achieved by secondary
intervention, the search for specific chemical etiology becomes
less urgent.
As soon as a chemical etiology has been suggested, primary
intervention should be considered to prevent further occurrence of
new cases or progression of the disease. Through this approach,
further proof of a causal relationship can frequently be obtained.
The results of a preliminary intervention will frequently give
rise to subsequent, more specific interventions that may further
support the causal relationship. Efforts in this area should
preferably include a control group, and the effects of the
intervention must be separated from the natural cycles of the
disease and the effects of other environmental factors. For
example, outbreaks of disease of chemical origin may be self-
limiting. The question of whether intervention occurred when the
number of cases was still increasing or whether they were already
decreasing at this time may be crucial. Examples of intervention
include the removal of contaminated food items from circulation and
the warning of the population against hazards, such as not to
consume grain treated with fungicide. Every effort should always
be made to identify and conduct intervention measures, in order to
augment disease prevention.
7.7. Confirmation of a Causal Relationship
After an association between a particular chemical and the
disease has been identified, the validity of the association should
be confirmed. The causal relationship could be supported, for
instance, through the detection of the toxic chemical or its
metabolites in tissues or biological fluids, or through laboratory
studies on appropriate experimental species, though, as discussed
in section 6, an animal model may not be readily identified.
Information on adverse effects in wild or domestic animals exposed
to the chemical factor may be useful in this regard. For example,
for confirmation of the involvement of aflatoxins in human
aflatoxic hepatitis, the contaminated corn grains consumed by
affected individuals were fed to ducklings, which then developed
bile-duct proliferation in the liver, which was typical of
aflatoxicosis (Krishnamachari et al., 1975).
Another means of confirmation is to relate the type, levels,
and extent of exposure to the chemical with previous or subsequent
disease outbreaks in human beings, if any. For example, the
clinical symptoms, levels of aflatoxins in the staple food, and
conditions of exposure during the outbreak of aflatoxic hepatitis
in Kenya were similar to those reported earlier from India.
Similarly, conditions related to veno-occlusive disease in India
associated with pyrrolizidine alkaloid contamination of food grains
were similar to those that caused the disease in Afghanistan.
Furthermore, the cause of endemically-occurring osteosclerosis was
discovered when a similar disease, skeletal fluorosis, was
described in workers exposed to excess levels of fluoride.
Ideally, when considering the association between the suspected
causal factor and the resulting disease, the overall evidence
accumulated should be critically reviewed, according to the
following established criteria discussed in detail by Susser (1973)
and Lilienfeld & Lilienfeld (1980):
(a) consistency of association, i.e., the repeated
observation of the connection between chemical
exposure and effects, under different circumstances;
(b) strength of association, i.e., more intense exposure
leads to more frequent or more severe effects;
(c) specificity of association, i.e., similar signs and
symptoms are not observed in the absence of the
suspected agent.
The criteria of time sequence and of coherence (biological
plausibility) and also of dose-response relationship were dealt
with in previous sections (7.3, 7.4, and 7.5, respectively).
However, all these criteria may sometimes be difficult to apply in
practice. Outbreaks of poisoning may be isolated events, and
idiosyncratic reactions or individual susceptibility may blur the
relationship to dosage levels. With chronic disease, where
chemical exposure constitutes only one of the risk factors, the
evaluation of the significance of a particular chemical exposure is
more difficult.
8. STEPS TO BE TAKEN FOLLOWING THE RECOGNITION OF THE CHEMICAL
ETIOLOGY OF AN OUTBREAK
Appropriate preventive measures must be implemented as soon as
is possible and feasible after the nature of the chemical agent,
the pathway of exposure, and the source have been identified.
Having determined the magnitude of the hazard in terms of the
size of population affected and the geographical areas involved,
the following public health measures should be undertaken in
addition to the obvious measures for the treatment and
rehabilitation of patients.
8.1. Preventive Action and Control
Strategies have to be planned for: (a) immediate steps to
control the outbreak; and (b) prevention of such outbreaks in the
future. Many of these steps have multisectorial implications and
need coordinated and integrated approaches for their success.
Immediate preventive measures depend on the type of chemical
involved and the pathway of exposure. If the contamination is
through food, steps have to be taken to seize and destroy the
damaged or contaminated food grain or food material, to prevent the
community from consuming such food, and alternative sources of food
must be made available. Wherever possible, the commodity should be
retrieved by cleaning or detoxifying under supervision. After
identifying the chemical(s) involved and their source, it may be
possible to prevent the entry of the chemical(s) into the food
chain. For example, recognition that pyrrolizidine alkaloids
contaminated food through the seeds of certain plants made it
possible to eradicate veno-occlusive disease by introducing simple
preventive measures, and removing the incriminating seeds from the
grain (Tandon & Tandon, 1975).
8.2. Surveillance and Monitoring System
A surveillance system should be established or strengthened in
all cases of chemically-induced disease, and should be suitably
designed according to the nature of the exposure. If the chemical
is identified and can be removed from the environment, apart from
monitoring for its recurrence in the environment, a long-term
follow-up, especially of the persons affected by the disease, may
be necessary. This is especially important if, according to known
experimental or human data, some health effects could manifest
after a period of time. This is of particular relevance for
carcinogenic effects. Thus, the creation of long-term machinery is
necessary for follow-up surveillance, including periodic physical
examination of the affected cases and monitoring for the appearance
of the earliest signs of the disease.
If the chemical has not been precisely identified, or if it
cannot be removed from the human environment, the following
surveillance measures are recommended:
(a) to ensure the reliability of disease-specific morbidity
and mortality data;
(b) to monitor the incidence, i.e., the occurrence of new
cases;
(c) to monitor changes in the distribution of the disease that
may indicate changes in exposures;
(d) to monitor the evolution of disease symptoms and
complications to initiate rehabilitation programmes, when
appropriate;
(e) to monitor specific environmental hazards, if identified.
A formal registry of cases is a valuable tool.
8.3. Health Education
With the identification of the chemical etiology of a disease
and the initiation of preventive steps, the need to disseminate the
information to the professionals involved and to educate the public
in appreciating the nature of the hazard, and ways and means of
preventing and minimizing them, cannot be over-emphasized. For
this purpose, the role of the mass media is particularly important.
To improve the preceptiveness of the medical and paramedical
personnel for such information, the medical/nursing/paramedical
curricula should include adequate sections on the role of chemicals
in contributing to disease.
9. THE NEED FOR INTERNATIONAL COOPERATION
9.1. Cooperation and Collaboration among Countries
Technical cooperation among countries is extremely important
because:
(a) The same diseases of suspected chemical etiology may be
found in several countries in different parts of the world
or in countries belonging to the same geographical area,
where the populations are exposed to the same
environmental hazards. Thus, there is a need for the
sharing of knowledge by countries with experience of the
endemic disease and for cooperative efforts in the control
of common public health problems. The relevant discussion
on Kashin-Beck disease can be found in Appendix III.
(b) There is a need for joint efforts in activities such as
the training of personnel, exchange of experts and
specialists, the use of sophisticated laboratory tests for
clinical diagnosis, and pathological and toxicological
studies.
(c) It is essential that clinical, epidemiological, and public
health information and experiences should be shared to
develop surveillance and monitoring activities for common,
and newly emerging, problems.
(d) Joint ventures in the field of research are necessary
concerning problems of common interest. This can be
facilitated by the establishment of "Sister Institutions"
dealing with the same problem in different countries.
(e) Cooperation among countries makes it possible to carry out
more extensive investigative programmes on common health
problems, which would exceed resources available in one
country, and to develop and implement preventive measures
of benefit to all of them.
(f) Mutual technical and economic assistance is needed in case
of disasters to deal with, and solve, emergency situations.
All these aspects should be considered in the context of the
social and economic development of the member countries, taking
into account the need for a multisectorial approach in the
prevention and control of diseases of chemical etiology.
9.2. Global and Regional Activities
The disease-oriented approach, which has been used when
establishing the role of certain chemicals in the etiology of
outbreaks of locally endemic diseases, has provided a basis for the
prevention and control of these diseases; thus, it must be
recognized as an important component of chemical safety. There is
a need to strengthen methodological cooperation at both the global
and regional levels, and the methodological component of the IPCS
has a well-defined role in this respect. It is also necessary to
develop, through the IPCS, regional and global registries of
endemic diseases with suspected chemical etiologies, to facilitate
the harmonization of activities aimed at improved understanding of
their causation, and at the prevention and control of these
diseases.
Thus, at both global and regional levels, there is a need to:
(a) Increase awareness of the potential of chemicals to induce
disease and of the need for international cooperation to
achieve the goal of chemical safety, including the
prevention and control of diseases of chemical etiology;
(b) Strengthen national capabilities in environmental
epidemiology, toxicology, and related fields;
(c) Promote and coordinate relevant research activities;
(d) Develop guidelines on environmental epidemiology;
(e) Identify relevant institutions at the country level to
promote training and research in the field;
(f) Apply health criteria in establishing national standards,
and in promoting the national regulations according to the
needs of the different countries and specific
epidemiological situations;
(g) Promote the evaluation of existing control programmes;
(h) Develop new, and improve existing, indicators to be used
in the epidemiological investigation of outbreaks of
disease and chronic endemic diseases, and for the
evaluation of control measures;
(i) Strengthen health monitoring and surveillance systems at
the country level;
(j) Strengthen the infrastructure of health services to
implement activities for the control of environmental
hazards, and to create or improve the surveillance system,
the laboratory capabilities, and the research institutions;
(k) Help member countries to establish a set of priorities for
chemical hazards control action within the framework of
health for all by the year 2000 and its main strategy,
primary health care.
9.3. Final Recommendations
In summary, the following three main recommendations should be
implemented through the global, regional, and country levels:
- to promote and stimulate the collaboration and cooperation
among member countries towards joint efforts for the
better knowledge and implementation of control measures in
common problems involving chemical safety;
- to accelerate and increase the training of specialized
personnel in the different regions and member countries;
- to promote and stimulate the collection and sharing of
clinical, epidemiological, and biological information
concerning outbreaks of disease and chronic endemic
diseases that are chemically-related.
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APPENDIX I. LIST OF BACKGROUND PAPERS
AMIN-ZAKI, Professor L.
A tale of two alkylmercury poisoning epidemics in Iraq
BABABUNMI, Professor E.A.
(a) Possible involvement of Cassava in certain tropical
endemic diseases
(b) A biochemical approach for establishing the role of
cyanide in the etiology of tropical ataxic neuropathy
BHAT, Dr R.V.
Endemic disease outbreaks in India due to chemical toxins
BORGONO, Dr J.
The problem of chemical etiology of certain human diseases
EGASHIRA, Dr Y.
An outline of history of research on Kashin-Beck disease
in Japan
GOYER, Dr R.A.
Identification of diseases caused by chemicals in the
environment
GRANDJEAN, Dr P.
Constraints in establishing the etiology of environmentally-
induced disease
IVANOV, Dr V.V.
Biochemical criteria of environmentally-induced diseases
KIMBROUGH, Dr R.D.
Investigation of acute outbreaks of human illness caused
by chemicals
KROGH, Professor P.
Strategies employed in the elucidation of causal associations
in human diseases caused by fungal and algal toxins
LEVANDER, Dr O.A.
Theories of nutritional deficiency in the etiology of
endemic diseases
MAHAFFEY, Dr K.R.
Techniques for investigating the etiology of disease
MARTIN-BOUYER, Dr G.
Thoughts on three epidemiological enquiries into
collective accidents due to a poison
SHIBATA, Professor S.
(a) Nephritogenic glycopeptide, nephritogenoside
(b) Vasculitis
TANDON, Professor H.D.
On investigating the chemical etiology of endemic diseases
and episodes or outbreaks of chemical poisoning with
special emphasis on developing countries
YANAGAWA, Professor H. & SHIGEMATSU, Professor I.
The epidemiological approach to the chemical etiology of
specific diseases: Itai-itai disease, Minamata disease,
and Yusho (PCB poisoning)
APPENDIX II. CONCEPTUAL FRAMEWORK USED IN SEVERAL STUDIES LEADING
TO IDENTIFICATION OF THE CHEMICAL ETIOLOGY OF OUTBREAKS OF DISEASE
INTRODUCTION
This framework, originally presented at the Task Group meeting
held in Beijing from 28 October to 8 November 1985, is based on
experience during studies on the aflatoxin-induced outbreak in
India (Tandon et al., 1977; WHO, 1979b) and the outbreaks of veno-
occlusive disease in Afghanistan (Tandon & Tandon, 1975; Tandon et
al., 1978b) and India (Tandon et al., 1976). It was amended at the
editorial meeting held in Geneva from 28 April to 2 May 1986, to
include as examples, studies in which a similar approach had been
used when establishing the chemical etiology of disease outbreaks
related to hexachlorophene (Martin-Bouyer et al., 1982) and
dicoumarine (Martin-Bouyer, 1983).
CONCEPTUAL FRAMEWORK
To investigate the etiology of a disease, follow a "disease-
oriented" approach as opposed to the classical toxicological
"substance-oriented" approach. Recognition of the occurrence of an
unusual disease is the initial requirement.
In order to be considered unusual, the disease entity may:
(a) be characterized by pathognomonic signs that do not occur
in a known disease;
(b) include non-specific clinical features, signs, and
symptoms and clinical laboratory and other data that do
not fit into a known disease category;
(c) be present as a cluster of cases of a disease that
normally occurs with a lower frequency; or
(d) be present as an endemic disease of unknown etiology.
The search for an etiology can be carried out in the following
three phases.
1. DESCRIPTIVE PHASE
After ascertaining that the disease is "unusual", the general
features of the disease, the circumstances under which it occurs,
and the size and nature of the population, or type of patients
involved, can be studied. The following steps are suggested:
1.1 Development of a Case Definition
For conducting an epidemiological study and to ensure the
uniformity of collected data, guidelines for screening the
population have to be developed. Criteria are needed for two
levels of screening, initial or mass screening and a later
screening that requires diagnostic criteria to confirm the cases.
1.1.1 Criteria for recognizing index cases during mass screening
Criteria for the identification of index cases consist of major
clinical signs and symptoms, for example:
(a) acute jaundice in the aflatoxin outbreak;
(b) rapidly developing ascites in the outbreak caused by
pyrrolizidine alkaloids;
(c) encephalitis with bullous dermatitis on buttocks in cases
of hexachlorophene toxicosis; and
(c) haemorrhagic syndrome in newborn infants, without fever in
cases of dicoumarine poisoning.
1.1.2 Criteria for confirming cases suspected in mass screening
These may include a combination of: symptoms, signs, laboratory
data, X-rays, etc, and pathological features.
The criteria selected in the studies used as examples in this
paper were:
(a) characteristic morphological features observed in the
liver biopsies in cases of toxicosis due to aflatoxins and
pyrrolizidine alkaloids;
(b) characteristic morphological lesion in the central nervous
system and presence of chemical in blood and bones at
autopsy, in cases of hexachlorophene poisoning; and
(c) bleeding diathesis consistent with avitaminosis K, in
cases of dicoumarine poisoning.
1.2 Descriptive Pattern of the Disease
This may include a study of the clinical features of the
disease, the dominant signs and symptoms, the clinical course of
the disease and, in case of an outbreak, an approximate idea of the
size of the population affected, the mortality rates, etc. Visits
to the field or site of occurrence by the investigating team, which
should include adequately trained clinical staff, are essential and
cannot be over-emphasized. Study of the habitat, and the family
style of living, cooking, and eating, may provide crucial clues.
The investigating team should mainly consist of persons with the
same cultural background as the affected population, or at least
persons familiar with it. In addition, the following information
can be obtained:
(a) Cluster analysis of cases, either according to factors
related to the physical environment, e.g., geographical,
seasonal, or to factors related to affected subjects,
e.g., age, sex, family structure, socio-economic status,
occupation.
(b) Retrospective study of health statistics of the area,
obtained through government, municipal, or county
data, or from hospitals and other health-care facilities
in the region.
(c) Pattern of illnesses in the affected area compared with
control area;
(d) Study of the original source of food and of food storage
practices;
(e) Identification of locally endemic diseases, if any.
In the case of a disease outbreak, reports providing some of
the above information and often important clues to the etiology of
the disease, especially if a similar disease has been known to
occur in the past, may be obtained from local general
practitioners, primary health/paramedical workers, health
officials, social workers, and school teachers.
1.3 Study of Locally Prevalent Animal Diseases
Unusual happenings, if any, should be noted in the fauna, farm
animals, and domestic animals.
2. HYPOTHESIS GENERATION PHASE
Having collected the descriptive data on the disease and the
above information, there may be possible clues suggesting, at
least, the nature of the likely etiological factor(s). While
generating a hypothesis, attention should be focused on the most
typical cases. The following steps are suggested:
2.1 Examination of Diseased Tissue
Examination of even one or two tissue specimens, especially the
main diseased organ, may provide crucial clues to the etiology of
the disease, particularly in the light of the descriptive pattern,
in the initial phases of the study. If available, the diseased
tissue of both animals and patients should be examined.
For example, in the study on the aflatoxin-induced outbreak,
the finding of syncitial giant cells in human liver tissue,
identical to those found in rhesus monkeys administered aflatoxin,
suggested mycotoxin etiology.
2.2 Possible Clues in the Environment
The following factors should be investigated:
(a) Unusual happenings in the environment, e.g., drought,
floods, heavier than normal rainfall, etc
(b) Opening of new industries, manufacture of new chemicals or
products using new chemicals, change in the manufacturing
process
(c) The use of pesticides/fungicides
(d) Introduction of new seed/agricultural practices, involving
the use of a new chemical
(e) Disposal of industrial waste
(f) House-keeping practices in the local industry
(g) Change in food habits
(h) Possible contamination of staple food/cooking medium
(i) The use of a new household chemical.
2.3 Consideration of Possible Routes of Exposure
Exposure usually occurs orally or via inhalation. However, the
more unusual dermal route of exposure should also be considered.
3. HYPOTHESIS-TESTING PHASE
On the basis of the above information, one or more etiological
factors may be suspected and a hypothesis generated, which then has
to be tested as described below:
3.1 Exploration of Reports of Occurrence of Similar Episodes or
Diseases Elsewhere in the World, Using Available Data Base Systems
3.2 Evolution of a Strategy for Further Study, Taking Into Account
the Specific Characteristics of the Suspected Agent
This step includes:
(a) Identification of specific biological markers of exposure
and of toxicity;
(b) Listing of laboratory procedures/analyses to be carried
out:
(i) in the field;
(ii) in local institutions;
(iii) at specialized laboratories;
(c) Establishment of range and type of epidemiological data to
be collected;
(d) Decisions on type and expertise of specialized personnel
required to conduct field study, besides essential
clinical and pathology-trained staff;
(e) Listing of toxicological studies to be carried out on
laboratory animals.
3.3 Collection of Additional Pathological Samples
Detailed autopsy/biopsy studies can be made on animals and
patients. A biopsy could be carried out as part of a diagnostic or
therapeutic procedure, for example, carrying out a liver
biopsy/kidney biopsy following paracentesis.
3.4 Collection and Storage of Biological and Environmental Samples
for Further Analysis
4. FOLLOW-UP EVALUATION
At the end of the entire process, after testing the validity of
the hypothesis and after establishing the causal relationship
between a chemical agent and the identified disease cases, the
following steps are necessary:
(a) Dissemination of knowledge concerning signs and symptoms
among health practitioners, in order to identify all cases
of the disease and to get an exact evaluation of the
magnitude of the outbreak/episode.
(b) Search for even milder signs and symptoms among
subpopulations that have been exposed to the agent. This
may result in the identification of borderline cases,
which will improve the accuracy of the evaluation.
(c) Identify the mechanism of the contamination and the
determinants of the exposure of specific subpopulations.
(d) Finally, identify the most relevant measures to either
remove the causal agent or minimize the exposure of the
population at risk.
APPENDIX III. SUMMARY REPORT ON THE IPCS/WPRO/PRC MEETING ON
KASHIN-BECK DISEASE
Background
Kashin-Beck disease was first described by Kashin and later by
Beck & Beck in the Urov River area of eastern Siberia in the last
century. Further research and practical measures in the USSR
resulted in the successful control of the endemic disease in this
area.
In China, this disease, which has probably existed in the
endemic regions for centuries, was first studied during the first
half of this century. However, it is only during the last decades
that this health problem, prevalent in 14 out of 29 provinces,
municipalities, and autonomous regions of mainland China, has
received appropriate attention. The basic pathological change in
this disease, commencing mainly in children, is the degeneration
and necrosis of articular cartilage and the growth plate, which can
result in permanent disability. Present estimates indicate that
about 2 million people are affected by this disease and that more
than 30 million people living in the endemic areas of China are at
risk of acquiring it. The disease seems to be linked with the
consumption of food produced in the endemic areas and is possibly
related to the presence of certain specific chemicals in food
and/or water. The People's Republic of China, expressing interest
in the WHO/ILO/UNEP International Programme on Chemical Safety
(IPCS), underlined the importance of this disease and, for this
reason, a joint meeting was convened by the Ministry of Public
Health of the People's Republic of China, the International
Programme on Chemical Safety, and the Western Pacific Regional
Office of the World Health Organization to review the status of
present knowledge on this disease and its possible etiology.
Scope of the Meeting
The meeting was held at the Institute of Health of the China
National Centre for Preventive Medicine, in Beijing, from
28 October to 1 November 1985. After the opening by Professor
Chen Chunming, Director the China National Centre for Preventive
Medicine, the meeting was addressed by Dr Guo Ziheng, Vice-Minister
of the Ministry of Public Health of the People's Republic of China,
who explained the importance of the meeting for the promotion of
studies on the chemical etiology of specific diseases. The Vice-
Minister stressed the importance of the fact that the meeting on
Kashin-Beck disease would be followed by a second IPCS meeting on
criteria for establishing the chemical etiology of specific
diseases as a basis for their prevention, which would be hosted by
the same Institute, during the following week. Dr E. Goon (WHO
Representative, Beijing) and Dr J. Parizek (IPCS/WHO) addressed the
meeting on behalf of WHO. Professor Chen Chunming was elected
Chairman, Professor V.A. Nasonova and Dr Niu Shiru, Vice-Chairmen,
and Dr Chen Junshi and Dr O.A. Levander, Rapporteurs. The
background papers for the meeting are listed in Appendix I.
The papers on Kashin-Beck disease presented at the meeting by
Chinese scientists reviewed:
(a) the epidemiology, geographical distribution, and
clinical features;
(b) pathological and biochemical features; and
(c) prevention of the disease.
In addition, a paper expressing the present views of a leading
scientist from the region in the USSR where Kashin-Beck disease is
endemic was presented, at the request of the organizers of the
meeting from the People's Republic of China.
During the last day, related papers were presented on Keshan
disease and of endemic human selenosis in China.
Summary of the results presented at the meeting: the current
situation concerning Kashin-Beck disease
1. Main epidemiological characteristics
(a) Geographical distribution
The disease mainly occurs in the mountainous and hilly areas of
temperate forest and forest-steppe zones and is very rarely
observed in the plains. The climate in endemic areas usually
includes a long period of frost and big differences between the
daily minimum and maximum temperatures. Affected villages are
distributed in small foci within the endemic area. The prevalence
in neighbouring villages can vary significantly and can change with
time. New patients can be found in villages where patients have
not been reported before. In rare cases, the prevalence in
certain, severely affected villages can decrease "spontaneously" so
that, after about 10 years, no new cases occur.
(b) Age of patients
The disease mainly develops in 5- to 13-year-old children, and
very few new cases are seen among adolescents and adults. In
heavily affected areas, some new cases might be only 2 - 3 years of
age, whereas, in lightly affected areas, some new cases may not
occur until 10 years of age.
(c) Family characteristics
Within endemic areas, patients mainly occur in farming
families. Children of farm (government-owned) employees are also
vulnerable). Only very few cases occur in "professional" families.
However, patients may occur in professional families, if they
consume a large amount of the staple grains (corn, highland barley,
wheat) produced in endemic areas. The incidence of new and severe
cases of the disease may decrease after changing the staple grains.
In contrast with other endemic diseases, such as Keshan
disease, it is important to note that, in some sites where Kashin-
Beck disease is endemic, in recent years, the number of recognized
cases is increasing. The etiology of the disease remains obscure,
but has been linked with certain chemical constituents of food and
possibly water. In China, Kashin-Beck disease mainly occurs in
low-selenium areas, but selenium deficiency alone is not sufficient
to explain the disease. The possible role of fungal (Fusarium
oxysporum) or bacterial toxins was considered in some of the
papers presented at the meeting.
2. Clinical signs and symptoms
In the clinical development of the disease, weakness is
followed by joint stiffness. Limitation of flexion of the index,
middle, and ring fingers towards the palm can be detected followed
by limitation of elbow joint movement and joint enlargement and
deformity. Signs are similar to those of primary osteoarthrosis.
In China, the disease has been clinically classified as follows:
- Early stage: flexion of distal joint part of fingers,
bow-like fingers, and pain in knee and ankle joints;
- First degree: enlargement and crepitus of small joints;
- Second degree: short fingers, enlargement and dysfunction
of medium-sized joints;
- Third degree: enlargement and dysfunction of large joints
(stunted growth).
"Muscular dystrophy" can be seen during the course of the disease.
X-ray examination reveals:
(a) the calcification line becoming blurred, thin, interrupted,
and disappearing as is characteristic for chondronecrosis;
(b) defects of the metaphyseal plate, the end of distal bone,
and carpal and metacarpal bones following chondronecrosis;
(c) deformity of the epiphysis, synostosis of the epiphyseal
plate resulting from necrosis of the whole layer of the
epiphyseal plate; and
(d) enlargement of joints and stubby fingers, the effects of
secondary osteoarthrosis.
Anatomical pathological examination reveals that lesions mainly
involve hyaline cartilage. The epiphyseal cartilage, articular
cartilage, and epiphyseal growth plate are the most affected sites.
Changes are "dystrophic" in nature. The most important
pathological feature is multiple localized chondronecrosis in the
deep portion of cartilage tissue. Chondronecrosis of the growth
plate may result in disturbance of endochondral ossification and
may even induce the early closure of the epiphyseal growth plate.
The growth of long bones ceases and causes short fingers and toes,
short limbs, and even stunted growth. The chondronecrosis in
articular cartilage may induce scar formation and result in bony
enlargement, osteophyte formation, and disfiguration of the joints
affected ("endemic osteoarthrosis deformans"). Disturbances of
endochondral ossification of the growth plate and advanced
secondary osteoarthrosis are the two cardinal manifestations of the
disease.
Biochemical research has indicated a series of metabolic
disorders including:
(a) changes in cartilage metabolism, mainly affecting
chondroitin sulfate and proteoglycan;
(b) changes in clinical chemistry, including the plasma
enzymes (e.g., alkaline phosphatase, glutamate-oxalo-
acetate transaminase, beta-hydroxybutyrate dehydro-
genase), and the urinary excretion of creatinine and
hydroxyproline;
(c) changes in the composition of certain lipids and selenium
in the red blood cell membranes; and
(d) characteristics of low-selenium status, including changes
in glutathione peroxidase activity, tocopherol content,
and lipid peroxides in plasma.
3. Preventive measures
The following techniques for the prevention of Kashin-Beck
disease have been studied by Chinese scientists and were discussed
at the meeting. All these approaches have been used in studies on
subpopulations of varying sizes, and positive results from
individual studies were reported at the meeting.
(a) Comprehensive prevention
Encourage the children to diversify their foods (variety and
source), offer two servings/week of soup containing soybeans, sea
weed, and multiple vitamins. Purify drinking-water (use deep well
water with precipitation) and improve personal hygiene. It has
been reported that, with this scheme, the prevalence of X-ray
changes and of changes in the metaphysis decreased.
(b) Selenium intervention
Three different measures have been used for selenium
supplementation including:
(i) oral administration of sodium selenite at 1 mg/week
or 2 mg/week to children of 7 - 10 years and 11 - 13
years, respectively;
(ii) selenized table salt containing a sodium selenite
concentration of 16.7 mg/kg; and
(iii) spraying sodium selenite solution on wheat crops at
the rate of 15 g/ha (1 g/mu)a.
Using these measures, incidence rates dropped within one year, and
recovery from changes in the metaphysis was noted.
(c) Water quality
Water can be purified by precipitation, filtration, and
chlorination. This technique and/or the use of deep groundwater
have both been associated with an improvement in clinical symptoms
and a reduction in incidence rate.
(d) Change of grains
Changing the locally produced grain for grains produced in
other areas led to the prevention of new cases, a decreased
incidence of X-ray changes, and better recovery from meta-physeal
changes.
In endemic areas of the USSR, significant reductions in the
prevalence rates and the severity of Kashin-Beck disease were
connected with special governmental and public health measures.
The most effective measures were the organization of population
migration from endemic to non-endemic regions, the importation of
food from non-endemic areas, thermal treatment of local products
and water, annual check-ups on children and adult populations in
endemic regions by public health personnel, and the development of
appropriate health education programmes. On the basis of the
theory of biogeochemical provinces linking certain endemic diseases
with the geochemical characteristics and quality of the soil and
water in certain areas, studies in the USSR related very high
phosphate and manganese contents in the soil, food, and drinking-
water in the endemic area with Kashin-Beck disease. Reducing the
contents of these chemicals in food and water is part of the
present preventive measures in the USSR. As mentioned in the
discussion, differences in selenium levels were not detected
between the affected and non-affected areas studied in the USSR.
4. Conclusions and recommendations
(a) Kashin-Beck disease is a highly disabling disease of
permanent character that mainly affects children. In China
alone, about 2 million people are affected, at present, and
more than 30 million people living in the endemic areas are at
direct risk of acquiring the disease. All the evidence
indicates that the disease is caused by a certain quality of
the environment, specific for the endemic regions, which
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a 1 mu = 0.0667 ha. From: Beijing Language Institute (1979)
Chinese English Dictionary, Beijing, Commercial Press.
encompass a large part of China and parts of neighbouring
countries. Several studies indicate the involvement of certain
chemicals in food and water (manganese, phosphorus, mycotoxins,
microbial toxins, humic acid, etc.), as well as nutritional
imbalance, in particular, selenium deficiency, as factors
contributing to the etiology of this disease.
A coordinated effort is needed to elucidate the etiology of
this disease, which is endemic in a very specific area of Asia.
Cooperation among countries affected by the disease should be
supported by international organizations with the aim of
developing uniform diagnostic criteria and protocols for
epidemiological studies to test the above hypotheses and
elucidate more precisely the cause of the disease and
contributing factors. Exchange of information on effective
measures for the prevention of the disease should be another
component of such intercountry cooperation, as well as the
training of personnel needed for preventive, diagnostic, and
therapeutic activities. As a first step in this direction,
exchange of scientists between the countries with endemic
regions should be supported as well as the development of
methods and their use in the above-mentioned cooperative
efforts.
Such activities would significantly contribute towards
chemical safety and the solution of a problem affecting
populations in several neighbouring member states.
(b) Kashin-Beck disease primarily affects the joints.
However, the relation with other osteoarthroses is not clear,
and the possible etiological factors involved are not known.
Thus, in cooperation with non-governmental and other
organizations, a meeting should be convened to define specific
characteristics, identify risk factors, and consider
possibilities for the prevention and control of this disease
and its possible relationship with other osteoarthroses.
(c) In spite of the public health significance of Kashin-Beck
disease, the disease does not seem to be sufficiently
recognized in the medical literature. In this respect, the
data presented at this meeting was considered highly
informative.
It was recommended that the co-sponsoring organizations should
explore the possibility of publishing the full proceedings of
this meeting as a monograph. The possibility of making the
video tape that was prepared in the endemic regions for the
meeting more widely available should also be explored.
ANNEX TO APPENDIX III. THE IPCS/WHO/PRC MEETING ON KASHIN-BECK
DISEASE
Participants
Professor L. Amin-Zaki, Consultant Paediatrician, Central Hospital,
Abu Dhabi, United Arab Emirates
Professor E.A. Bababunmi, Director, Laboratory of Biomembrane
Research, Department of Biochemistry, University of Ibadan,
College of Medicine, Ibadan, Nigeria
Dr R.V. Bhat, National Institute of Nutrition, Indian Council of
Medical Research, Hyderabad, India
Dr J. Borgoño, Professor of Preventive Medicine, University of
Chile, Chief, Department of International Affairs, Ministry of
Health, Santiago, Chile
Dr Y. Egashira, Honorary Staff, National Institute of Health,
Hatano Research Institute, Food and Drug Research Centre,
Hatanoshi, Kanagawa-ken, Japan
Dr R.A. Goyer, Deputy Director, National Institute of Environmental
Health Sciences, Research Triangle Park, North Carolina, USA
Dr P. Grandjean, Institute of Community Health, Department of
Environmental Medicine, Odense University, Odense, Denmark
Dr V.N. Ivanov, Director, Chita Medical Institute, Chita, USSR
Dr V.V. Ivanov, Chief, Department of Pathophysiology, Krasnoyarsk
Medical Institute, Krasnoyarsk, USSR
Dr R.D. Kimbrough, Research Medical Officer, Toxicology Branch,
Clinical Chemistry Division, Bureau of Laboratories, Center for
Environmental Health, Centers for Disease Control, Atlanta,
Georgia, USA
Professor P. Krogh, Department of Microbiology, Royal Dental
College, Copenhagen, Denmark
Dr O.A. Levander, Vitamin and Mineral Nutrition Laboratory,
Nutrition Institute, US Department of Agriculture, Beltsville,
Maryland, USA (Co-Rapporteur)
Dr K.R. Mahaffey, Division of Standards Development and Technology
Transfer, National Institute for Occupational Safety and Health,
Cincinnati, Ohio, USA
Dr G. Martin-Bouyer, Conseiller Technique, Ministère des Affaires
Sociales et de la Solidarité Nationale, Direction Générale de la
Santé, Paris, France
Professor V.A. Nasonova, Director, Institute of Rheumatology,
Academy of Medical Sciences of the USSR, Moscow, USSR
(Vice-Chairman)
Professor H.D. Tandon, formerly Director, All India Institute of
Medical Sciences, New Delhi, India
Professor H. Yanagawa, Department of Public Health, Jichi Medical
School, Minamikawachi, Tochigi-ken, Japan
Dr Bai Shicheng, The Basic Medical Institute of Liaoning Province,
Shenyang, People's Republic of China
Professor Chen Chunming, Director, China National Center for
Preventive Medicine (CNCPM), Beijing, People's Republic of
China (Chairman)
Dr Chen Junshi, Deputy Director, Department of Nutrition and Food
Hygiene, Institute of Health, China National Centre for
Preventive Medicine, Beijing, People's Republic of China
(Rapporteur)
Dr Chen Xiaoshu, Deputy Director, Institute of Health, China
National Centre for Preventive Medicine, Beijing, People's
Republic of China
Dr Deng Jiayun, The Health and Antiepidemic Station of Sichuan
Province, Chengdu, People's Republic of China
Dr Geng Jinzhong, Deputy Director, Division of Environmental
Hygiene, Ministry of Public Health, Beijing, People's Republic
of China
Dr Guo Xiong, Research Laboratory of Endemic Bone Disease, Xian
Medical University, Xian, People's Republic of China
Professor Li Fangsheng, The Basic Medical Institute of Liaoning
Province, Shenyang, People's Republic of China
Dr Li Guangshen, Institute of Endemic Disease, Norman Bethune
University of Medical Sciences, Changchun, Jilin Province,
People's Republic of China
Professor Li Jiyun, Northwestern Institute of Soil and Water
Conservation, Chinese Academy of Sciences, Shaanxi, People's
Republic of China
Dr Li Sheng, Deputy Director, Division of Technical Assistance
and Development, China National Center for Preventive Medicine,
Beijing, People's Republic of China
Dr Li Chongzheng, Institute of Prevention and Cure of Endemic
Diseases, Gansu Province, People's Republic of China
Dr Liang Shutang, Institute of Prevention and Cure of Endemic
Diseases, Shaanxi Province, People's Republic of China
Dr Ma Tai, Tianjin Medical College, Tianjin, People's Republic of
China
Dr Mo Dongxu, Research Laboratory of Endemic Bone Diseases, Xian
Medical University, Xian, People's Republic of China
Dr Niu Guanghou, The Health and Antiepidemic Station of
Heilongjiang Province, Haerbin, People's Republic of China
Professor Niu Shiru, Director, Institute of Health, China
National Centre for Preventive Medicine, Beijing, People's
Republic of China (Vice-Chairman)
Professor Peng An, Institute of Environmental Chemistry, Chinese
Academy of Sciences, Beijing, People's Republic of China
Professor Ren Hongzao, The Basic Medical Institute of Liaoning
Province, Shenyang, People's Republic of China
Dr S. Shibata, Director, Division of Clinical Research, National
Medical Centre of Japan
Dr Sun Xi, Head, Division of Science and Technology, Office for
Endemic Diseases (CPCCC), Shenyang, People's Republic of China
Professor Tan Jianan, Institute of Geography, Chinese Academy of
Sciences, Beijing, People's Republic of China
Dr Xi Guangzeng, The 323 Hospital of the People's Liberation Army,
Xian, People's Republic of China
Dr Xu Guanglu, Research Laboratory of Keshan Disease, Xian Medical
University, Xian, People's Republic of China
Professor Yang Fuyu, Institute of Biophysics, Chinese Academy of
Sciences, Beijing, People's Republic of China
Professor Yang Guangqi, Department of Nutrition and Food Hygiene,
Institute of Health, China National Centre for Preventive
Medicine, Beijing, People's Republic of China
Professor Yang Jianbo, Haerbin Medical University, Haerbin,
People's Republic of China
Professor Yang Tongshu, Institute of Endemic Disease, Normal
Bethune University of Medical Sciences, Changchun, People's
Republic of China
Dr Yin Peipu, Institute of Endemic Bone Diseases, Xian Medical
University, Xian, People's Republic of China
Dr Ying Mingxin, Haerbin Medical University, Haerbin, People's
Republic of China
Professor Yu Weihan, Haerbin Medical University, Haerbin, People's
Republic of China
Dr Zhai Shusheng, The Second Institute of Prevention and Cure of
Endemic Diseases, Jilin Province, People's Republic of China
Dr Zhao Tieli, Deputy Director, Office for Prevention of Endemic
Diseases (CPCCC), Shenyang, People's Republic of China
Dr Zhou Zhenglong, Institute of Prevention and Cure of Endemic
Diseases, Shanxi Province, People's Republic of China
Representatives from Other Organizations
Dr R. Hoffmann, Senior Programme Officer, United Nations Children's
Fund (UNICEF), Beijing, People's Republic of Chinaa
Dr Zhang Naizheng, International League Against Rheumatism (ILAR),
Capital Hospital, Chinese Academy of Medical Sciences, Beijing,
People's Republic of China
Secretariat
Dr Eric H.T. Goon, WHO Representative and Programme Coordinator,
Beijing, People's Republic of China
Dr M. Mercier, International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland
Dr M. Mitrofanov, Division of Noncommunicable Diseases, World
Health Organization, Geneva, Switzerland
Dr J. Parizek, International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland (Secretary)
Dr Xu Genlin, Director, Office of Research Management, Institute of
Health, Beijing, People's Republic of China
Dr Yao Peipei, Division of Pneumoconiosis, Institute of Health,
Beijing, People's Republic of China
Dr Liu Yuying, Division of Industrial Toxicology, Institute of
Health, Beijing, People's Republic of China
Dr Wang Zhiwu, Institute of Kashin-Beck Disease of Heilong-jiang
Province, Haerbin, People's Republic of China
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a Attended the opening of the meeting.