Use of Epidemiological and Toxicological Observations in Domestic and Wild Animal Populations for Evaluating Human Health Risks

Domesticated and wild animal populations are important resources in evaluating human health risks. Animals not only share man's environment, but some of them are also part of the human food chain. Three examples of monitoring the health of animal populations and using these data in evaluating human health risk were reviewed. A study of horses, cattle and wildlife in a Missouri lead mining and smelting area revealed that horses were sensitive indicators of environmental lead contamination; they developed clinical signs of lead poisoning and died, while other animal species in the same area did not exhibit signs of illness. Although they did not appear ill, cattle in the same area had liver and kidney lead concentrations that were higher than tolerance levels established in England, Wales and Canada. Wildlife such as bullfrogs, muskrats, and greenbacked herons collected downstream from an old lead mining area had significantly higher lead and cadmium levels than either upstream samples or comparable downstream samples collected at a new lead mining area. Some of these data were used in a court trial which resulted in the lead company buying the farmland so that humans and domestic animals would not be exposed. Another study of municipal sludge application on Ohio farms did not reveal excess illness rates for either livestock or humans living on farms receiving the sludge, as compared with those on control farms. However, cattle were more sensitive than humans as early indicators of low level exposure to toxic heavy metals such as cadmium and lead. Also, calves on sludge-receiving farms accumulated cadmium and lead in their kidneys. The National Animal Health Monitoring System (NAHMS), currently in a pilot stage in eight states, is another example of the use of animal populations to evaluate human health risk. Information from NAHMS about zoonotic infections, use of drugs in food producing animals and diseases common to both animals and man, provide a better understanding of human disease. Population-based animal studies are desirable adjuncts to laboratory animal studies in assessing human health risk due to environmental exposure.