Comprehensive guidelines to assist practitioners with prevention, clinical signs, diagnostic sampling and other considerations of Eastern Equine Encephalitis (EEE), an arbovirus in which mortality can exceed 90% in naïve horses, have been published on the AAEP’s website and On-the-Go app.

EEE has particular prevalence in the southeastern United States, although recent cases have been reported as far west as Texas and north into eastern Canada. Indirect transmission to horses occurs through bites from infected mosquitos. EEE is considered a core vaccine, and the mortality rate is lower in horses with previous vaccination or partial protection. Death usually occurs within three days of the onset of clinical signs; horses that survive may have permanent neurologic deficits, including abnormal mention and/or residual ataxia.

“Eastern Equine Encephalitis continues to be a concern,” said Barbara Jones, DVM, MPH, DACVPM, principal at One Health Consulting, LLC and president of the American College of Veterinary Preventive Medicine. “The updated guidelines ensure practitioners have the latest information on incubation period, and currently recommended diagnostic tests.”

Besides vaccination, vector control through comprehensive mosquito mitigation efforts is strongly encouraged. As an OIE-reportable disease, suspected cases should be reported to the US Department of Agriculture and state animal health officials.

Dr. Jones co-authored the Eastern Equine Encephalitis Guidelines with Angela Pelzel-McCluskey, DVM, MS, national epidemiologist for equine diseases at USDA APHIS Veterinary Services. The guidelines were reviewed and approved by the AAEP’s Infectious Disease Committee and board of directors. View the guidelines or save them to your mobile device at

AAEP guidelines for 24 other equine infectious diseases are available at In addition, six foreign animal disease guidelines can be found at

About AAEP

The American Association of Equine Practitioners, headquartered in Lexington, Ky., was founded in 1954 as a non-profit organization dedicated to the health and welfare of the horse. Currently, AAEP reaches more than 5 million horse owners through its over 9,000 members.

Publish Date

April 4, 2023

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