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OCR for page 131
8 Conclusions and Recommendations
The value of using domestic and wild animals to identify and monitor a wide
variety of environmental hazards to human health and ecosystems has been
discussed throughout this report. This report has described epidemiologic and
experimental approaches to the use of animals as environmental sentinels to
detect hazards before they would be discovered with more traditional meth-
ods—human epidemiologic studies or laboratory-animal experiments. The
committee noted that many current animal-monitoring systems could, with
relatively minor modifications, be made suitable for use during the process of
risk assessment of many environmental contaminants. These would comple-
ment traditional rodent models by aclding species diversity and a method to
evaluate natural and often complex exposures.
Despite the wealth of studies of and scientists' and regulators' interest in the
use of animals as sentinels for environmental health hazard, the committee
notes that this approach has not gained widespread acceptance. One reason
might be the institutional inertia that accompanies integration of new scientific
methods into the risk-assessment process and use of the results for risk man-
agement. Many government agencies do not recognize the importance of
animals sentinels or agree on how to compare the findings obtained with them
and the findings obtained with more traditional methods. In addition, re-
search on and development of animals sentinels have generally not had high
priority in funding agencies, although they probably will with increasing atten-
tion to animal welfare and the search for humane alternatives to laboratory-
animal experimentation. The committee feels that potential users of animal-
sentinel data generally are not aware of possible applications of these alterna-
tive methods and that traditional rodent models for toxicity testing are per-
ceived as superior to such alternative methods.
The committee concludes that various factors have contributed to the un-
deruse and lack of synthesis of data from animal sentinel systems:
· The data collected by most animals sentinel systems have not been
131
OCR for page 132
132 ANIA~1LS AS SENTINELS
standardized, and data-collection programs themselves have been poorly coor-
dinated and lack specific and realistic objectives.
· Basic information on the biology, behavior, and similar characteristics
of many potentially useful species of sentinel animals is insufficient.
· The predictive value of animal sentinel data for human health usually
has not been evaluated sufficiently.
· The predictive value for human health of any data obtained from ani-
mals has inherent uncertainties, because it is difficult to extrapolate them to
humans.
· The concept and methods of risk assessment have generally not received
sufficient attention in training programs in veterinary epidemiology, toxicology,
pathology, and environmental health.
Perhaps most important, the committee concludes that the communication
vital to development, refinement, and implementation of animal sentinel pro-
grams is lacking. Input from relevant government agencies, industry, and
academic institution will be required, if animals sentinel programs are to be
appropriately developed and operated.
Animal sentinel systems are particularly well suited for monitoring the
complex array of environmental insults to human health and for assessing the
health of delicately balanced ecosystems. Animal sentinels have three primary
strengths:
· They share environments with humans, often consuming the same foods
and water from the sources, breathing the same air, and experiencing similar
stresses imposed by technologic advances and human conflicts.
· Animals and humans respond to many toxic agents in analogous ways,
often developing similar environmentally induced diseases by the same patho-
genetic mechanisms.
· Animals often develop environmentally induced pathologic conditions
more rapidly than humans, because they have shorter lifespans; that results in
decreased latency periods for disease development or increased susceptibility
to toxic chemicals.
Keeping in mind those characteristics and potential advantages of animals
as sentinels of environmental health hazards, the committee offers the follow-
ing recommendations for the use of animals sentinels in risk assessment:
Animal diseases that can serve as sentinel events to identify environ-
mental health' hazards for humans or to indicate insults to an eco-
syste~n should be legally reportable to appropriate state or federal
health agencies.
OCR for page 133
CONCLUSIONS AND RECOMMENDATIONS 133
The committee recognizes the important contribution of the systematic
(and often mandatory) reporting of infectious diseases to the decline in human
and animal morbidity and mortality during the past century. The decline has
been particularly dramatic for diseases that are naturally transmitted from
animals to humans, such as rabies, brucellosis, and tuberculosis. If mandatory
reporting of infectious diseases of animals were expanded to include occur-
rences of conditions or diseases with known environmental causes, these
occurrences could serve as sentinel events for potential environmental hazards
for human health. For example, acute lead poisoning in a pet dog alerts us
to the risk of chronic lead poisoning of children in the same household; and
the occurrence of mesothelioma in a pet dog suggests the presence in the
home of dangerous concentrations of asbestos years before adverse health
effects might be elected to be seen in the pet's owners. Such sentinel events
can be useful, if programs are established to collect data on specified environ-
mentally caused diseases, the information is disseminated promptly to health
agencies, and a followup mechanism is established to investigate each occur-
rence.
Olden reporting systems are established for environmental diseases
of animals in a defined geographic area, every appropriate effort
should be made to compare the frequency and pattern of these dis-
eases with those of corresponding diseases in humans, and it should
be determined whether animals can provide early warning of health
hazards to humans.
The committee recommends establishing systems for collecting data on
parallel diseases of animals and humans living in the same environments. In
numerous cases, ~ recognizable disease occurred in animals many years before
an epidemic of the same disease was observed in humans (e.g., feline into
lion and human neurologic disease resulting from ingestion of mercury-con-
taminated fish and shellfish from Minimata Bay, Japan). Parallel monitoring
of multiple animals species not only will provide early warning, but is likely to
provide clues to the etiology and pathogenesis of diseases that cannot be
evaluated with laboratory animals or other traditional approaches. To be
effective, such parallel data collection will require close coordination among
specialists in veterinary and human epidemiology, including the standardization
of disease nomenclature, coding schemes, and reporting methods.
The pet population in the United States should be estimated either
with statistical sampling or through incorporation of a few pertinent
animal-ownership questions into the census of the human popula-
tion.
OCR for page 134
134 ANIMALS AS SENTINELS
Disease surveillance is an important element of risk assessment. However,
In the absence of accurate data on the number of companion animals, it Is not
possible to compare the incidences or prevalences of particular diseases or
conditions of environmental importance In companion animals and humans
defined geographic areas. The absence of such information hinders the ex-
trapolation of data on many conditions that affect companion animals.
The committee recognizes that epidemiologic research and disease surveil-
lance require knowledge of the number and distribution of the persons who
are at risk of exposure and disease. That knowledge typically yields denomi-
nators for expressions of risk—i.e., incidence or prevalence in a given popula-
tion. In humans, the denominators are generally derived from a census or
special survey. Similar information is needed on companion-animal popula-
tions.
Food-animal and wildlife populations should continue to be determined
with a variety of methods by the U.S. Department of Agriculture and the Fish
and Wildlife Service, respectively, and by other appropriate agencies.
However, greater coordination is needed among surveyors of animal popu-
lations in the United States and worldwide.
Existing animal sentinel systems should be coordinated on regional
and national scales to avoid duplication of effort arid maximize use
of resources, arid standarization of methods and approaches should
be encouraged.
This report documents a wide variety of animal sentinel systems used at
local, regional, or national scales. Most of the monitoring systems were estab-
fished for specific purposes and generally have achieved their stated goals.
However, the programs overlap significantly, and some problems underuse
data and samples collected. For example, the Market Cattle Identification
program provides the framework suitable for a national cattle contaminants
monitoring program. In an era of diminishing financial resources, reigonal or
national coordination of existing programs could result In a large increase In
information about environmental contamination with a minimal increase In
monetary commitment. The Chesapeake Bay program is an example of a
successful coordination of private, state, and federal monitoring efforts.
Computer equipment, software, nomenclature, coding, data collec-
tion, and quality control should be standardized to facilitate coordi-
nation and collaboration in animal exposure and disease record
systems, and such systems should be used for fish and wildlife spe-
cies, as well as for companion animals and livestock. Geographic
OCR for page 135
CONCLUSIONS AND RECOMMENDATIONS 135
information system (GIS) technology should be used whenever am
propnate.
Many of the advantages of standardization and GIS technology for the
study of environmentally related diseases have been discussed. Veterinary
practitioners, diagnostic laboratories, veterinary teaching hospitals, and fish-
and wildlife-disease investigative Units all have information likely to be rele-
vant to animal sentinel systems and should be encouraged to standardize and
share their data bases. The importance of exposure and disease data for
human health risk assessment of environmental hazards, as well as for evaluat-
ing animal health itself, dictates that uniformity of data bases be given a high
priority.
The storage of large amounts of animal data in a logically retrievable form
that retains the geographic integrity of information is a central aspect of GIS
technology. The trend toward greater use of GIS technology will continue as
computer hardware and software improve and understanding of the complexity
of environmental issues increases. For GIS technology to be effectively inte-
grated into animal sentinel programs, a substantial commitment must be made
to identify the proposed uses of the data generated and to incorporate existing
exposure and disease data into the GIS.
Research should be emphasized for development of correlative rela-
fionships that reduce the uncertainly in animal to human extrapola-
tions and how animal sentinels should be used in the risk assess-
ment process.
Most of the existing animal sentinel systems are designed to measure e~o-
sure and effects In the animals either to determine environmental contam~na-
tion or contamination of the human food web. Estimates of human risk often
are made by extrapolation with very few data to support the validity of the
extrapolation. Safety factors are included in the risk assessment process to
account for the unknown differences between human and animal exposures
and sensitivities. Research in comparative toxicology is needed to develop
models that predict relative sensitivity of humans and various animals species
to environmental contaminants. Additional research is needed to establish
guidelines for how data from animal sentinel systems should be used in hi
and environmental risk assessments.
Support for academic courses and graduate programs in epidemiolo-
gy at colleges of veterinary medicine and colleges of biologic sciences
should increase, and emphasis should be placed on environmental
OCR for page 136
136 ANIM'4LSAS SENTINELS
tat health. A goal of such centers should be development of meth-
o~s for the use of animal exposure and disease data in human and
environmental health risk assessment.
Human and environmental health risk assessment involves many academic
disciplines, including biologic, physiology, epidemiology, immunology, to~ncolo-
gy, pathology, biostatistics, and veterinary and human medicine. Centers of
excellence in environmental health with such expertise should be developed,
with a focus on methods and programs for the use of animal sentinels. Each
center might emphasize a different type of sentinel, such as food animals,
companion animals, and wildlife, including fish, birds, bivalve mollusks, and
other invertebrates.
The committee recognizes that too few veterinary scientists are trained in
epidemiology and that even fewer are trained in environmental health and are
knowledgeable in risk assessment as it is related to the use of animals. The
expertise necessary to develop scientifically useful animal-disease data bases,
to coordinate existing data resources, and to use the resulting information to
identify environmental hazards has been a limiting factor in risk assessment.
Schools of public health traditionally have provided trading in epidemiology,
but their emphasis has been on human health and disease. There are no
schools of veterinary public health, and epidemiology programs in the schools
of veterinary medicine generally do not have enough external funding to estab-
lish the expertise that would be needed to support research and learning in
environmental epiclemiology.
If graduate training programs in veterinary epidemiology are to address
complex environmental issues adequately, they must use an interdisciplinary
approach. Environmental epidemiologists, in addition to being trained in
quantitative research methods, must be familiar with biotechnologic advances
in the various academic disciplines, such as molecular biology. The programs
should also provide an opportunity for students to observe the practices of risk
assessment and risk management by public-health officials, regulatory agen-
cies, and industry.
Representative terms from entire chapter:
environmental hazards
