Commentary: Epidemiology a Key Component of Equine Health

"Epidemiology is the study of the distribution and determinants of health-related states or events in specific populations and the application of this study to control health problems."
- J.M. Last: A Dictionary of Epidemiology, ed 2. New York, Oxford University Press, 1988.

While a definition is a good place to start when thinking about the role of epidemiology in equine health, for some people it is a bit formal and vague. Perhaps a more useful approach would be to consider the current applications of epidemiology to animal health and the benefits to be gained through epidemiological studies. To paraphrase a recent television advertising campaign, what can epi do for you?

While public health practice has currently placed an emphasis on determining risk factors and interventions for chronic conditions such as cardiovascular disease, diabetes, and cancer, the epidemiological focus in the veterinary community is directed at infectious/communicable diseases. There are exceptions, such as examining the risks for injury in performance horses or tracing of animal feed contaminated with melamine, but for the most part, infectious agents such as bacteria, viruses, and prions rule the day. This focus is a reflection of the population-based approach that veterinary medicine uses in dealing with infectious disease conditions and the recognition of the financial burden to both producer and consumer when infectious agents gain access to commercial agricultural systems.

Epidemiologic methods are used to address issues of equine health. The investigation of encephalitis attributed to West Nile virus in horses residing on long island, New York, in 1999 identified risk factors for exposure: stabling near water sources and areas of dense foliage. Studies also quantified the morbidity and mortality among horses residing in areas known to harbor infected mosquitoes (a clinical attack rate of 32% [25/79] with a corresponding case fatality rate of 36% [9/25] in exposed, unvaccinated horses), and predicted the geographic and temporal spread to other states--to the West coast over a four-to-five year period. These epidemiologic studies provided critical information for equine and public health for this foreign animal disease, which is now endemic to North America.

More recently, the diagnosis and epidemiological follow-up to the occurrence of equine arteritis virus in Quarter horses in the western United States demonstrated the ease with which a venereal disease can be dispersed across a large geographic area. The use of shipped, cooled semen demonstrated the need for industry-based interventions, such as the establishment of a code of practice for managing the health of equines used in commercial breeding.

For most purposes, simply tracing equines in commerce in order to evaluate their disease status (for example, with a certificate of veterinary inspection) or the status of other commingled animals (through testing for equine infectious anemia) may be all that is desired. For others, quantifying the risk for exposure to specific diseases, either emerging or domestic, is paramount. The important concept to remember is that the utility of any epidemiologically derived information will reside with the end user.

What can epi do for you?

Contact: Dr. Barry Meade; 502/848-2043; USDA-APHIS-VS, Frankfort, Kentucky.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

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Equine Disease Quarterly

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