Vaccinate Early to Combat Eastern Equine Encephalomyelitis

With 33 cases of Eastern equine encephalomyelitis (EEE) reported in Wisconsin alone last year, horse owners are encouraged to vaccinate for the mosquito-borne viral disease as part of the routine spring work their veterinarian offers. With its high mortality rate and lack of effective treatment, EEE poses a serious threat to the health of horses.

“The vast majority of the cases that were diagnosed and reported in Wisconsin ended in death or euthanization,” said Robert Ehlenfeldt, DVM, Wisconsin state veterinarian. “From what we have heard from veterinarians, there were likely more cases that went undiagnosed. The vaccination is inexpensive and readily available, but people get complacent when they don’t hear about a disease for a few years. I’m guessing there will be a strong demand for EEE vaccines in Wisconsin this year.”

EEE is transmitted to horses by mosquitoes that have become infected after feeding on birds that are carrying the virus. Early clinical signs of EEE are nonspecific, but can include fever, poor appetite, and stiffness. Once the disease progresses, clinical signs escalate to aggression, excitability, stumbling, circling, head pressing, head tilt, muscle trembling, and twitching. In its final stage, EEE can cause complete paralysis.

“This disease has a mortality rate near 90%,” relayed April Knudson, DVM, equine specialist for Merial Veterinary Services. “There is no treatment for EEE--only supportive care--and the small percentage of horses that survive may have permanent brain damage or long-term health issues. Vaccinating to help prevent EEE is far more affordable than the cost of supportive care that may or may not restore the horse to its same quality of life."

Although Wisconsin was particularly hard hit last year, EEE was also confirmed in several other states, including Michigan, New York, Florida, and Louisiana. Nationwide, 58 cases were reported. In 2010, there were 247 cases reported. Historically, cases of EEE have been reported in all states east of the Mississippi River, as well as in a number of western states.

Regardless of whether they live in an area that has experienced confirmed cases of EEE or other equine diseases, horse owners and veterinarians need to be aware of potential threats. Merial’s Outbreak Alert program tracks reported cases of EEE, West Nile virus, Wester equine encephalomyelitis, equine herpesvirus, rabies, equine influenza, and Potomac horse fever. Individuals that have signed up for the service receive texts and/or e-mail messages alerting them of confirmed threats in their area.

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