Monitoring and Surveillance of Equine Infectious Diseases

Disease monitoring is the ongoing systematic collection, analysis, and distribution of health-related information. Surveillance is a process that is specific for a particular disease within a defined monitoring system and implies that an intervention strategy will be initiated at some predetermined threshold level. For a disease like equine infectious anemia (EIA) or cases of a foreign animal or transboundary disease, an intervention is initiated with the detection of a single case. For other diseases, mitigation activities begin only if multiple cases are observed or the disease event occurs in an environment where spread to other equids is likely.

The main purpose of veterinary monitoring and surveillance is to provide a basis on which rational decisions can be made concerning the control and prevention of infectious and/or communicable diseases that affect animal populations. For equids, the goals are to minimize the impact of disease on the health and welfare of the equine population and to prevent disruption in commerce or trade. Disease surveillance also benefits public health: equine infections with West Nile virus or Eastern equine encephalomyelitis virus indicate that people are also at risk within a locale.

Monitoring and surveillance systems are tailored to a specific set of objectives that generally include estimation of disease frequency (temporal and geographic distribution); certification that animals, farms, states, or countries are free of a disease; and detection of foreign animal or emerging diseases. Any surveillance system should be evaluated periodically and assessed through a formal review process. The Centers for Disease Control and Prevention has published guidelines1 for evaluating surveillance systems that are applicable to human and veterinary diseases.

Equine disease surveillance data are collected most commonly from diseased animal cases. Diagnostic testing required by breed associations, a compulsory industry-initiated testing program, or interstate or international travel requirements also provides valuable data. While reports from veterinary diagnostic laboratories, academic institutions, or equine clinics constitute the majority of veterinary surveillance data, reporting by veterinary practitioners to animal health regulatory officials of infectious diseases is an invaluable component of a comprehensive surveillance system.

Surveillance denotes a process whereby animals are evaluated for evidence of past or present exposure to a particular infectious agent based on a formal sampling protocol; it is most useful in estimating disease prevalence. Currently, the United States Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services (USDA-APHIS-VS) is conducting, at the request of the United States Animal Health Association (USAHA) Infectious Diseases of Horses Committee, a targeted sampling of domestic horses in an effort to establish a national prevalence estimate for equine piroplasmosis caused by Babesia caballi and Theileria equi.

The decision to monitor a specific equine disease is made at the state level. While some diseases can result in excessive losses in equine populations, if they are ubiquitous in distribution, such as Rhodococcus equi infections or leptospirosis, they are not readily amenable to interventions.

The USDA's National Surveillance Unit recently established a Web site where the public can obtain up-to-date surveillance information, including maps that show the number and distribution of cases of EIA, vesicular stomatitis, and West Nile virus encephalitis. While the scope and quantity of available data is not extensive, it provides for a uniform method of reporting and has the potential to provide a central repository for national equine surveillance data.

1CDC. Recommendations from the Guidelines working group. Updated guidelines for evaluating public health surveillance systems. MMWR 2001;50 (No. RR -13).

CONTACT: Dr. Barry Meade, 502/848-2043, barry.meade@aphis.usda.gov; APHIS-USDA-VS, Frankfort, Ky.; or Dr. Peter Timoney, 859/257-4757, ptimoney@uky.edu; Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, Ky.

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

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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