Mississippi State Reports Surge in EEE, WNV Cases

Eastern equine encephalitis (EEE) and West Nile virus (WNV) have hit Mississippi's horses hard this year, with EEE case numbers surging to more than double 2006 levels. According to State Veterinarian Jim Watson, DVM, there have been 27 cases of EEE and 11 of WNV thus far.

Watson said there's no clear reason why the incidence of the mosquito-borne viruses has increased, especially given the exceptionally dry conditions experienced in much of the state this summer.

"It just fluctuates from year to year," Watson said. "I don't know that I can say why that might be--it's always a dilemma trying to figure out why some years are worse than others. "

According to the equine arbovirus reports compiled by the USDA's National Animal Health Surveillance System (NAHSS), a national reporting system for equine disease, there were 12 cases of EEE in Mississippi last year, along with 25 WNV cases. Nationally, there were 111 cases of EEE in the United States last year, along with 1,086 equine WNV cases.

Watson said arboviruses are a known problem for equines in the Gulf Coast states, and that nearly every Mississippi county has reported either EEE or WNV. He encouraged all horse owners the to utilize vaccines--which are widely available--for both viruses early in the year, before cases begin popping up.

"You don't want to wait until you hear about cases in your area," Watson said. "If you're in Louisiana, Mississippi, or Alabama, your horses are going to be exposed to EEE and West Nile virus and they need to be kept current on those vaccinations. You can't really predict, based on weather patterns or rainfall, who's going to be most susceptible.

"You have to assume that wherever you are there's the potential for virus activity--so take precaution," Watson said. "For horses, that includes vaccines."

Watson said that while many horse owners are paying attention to West Nile virus, they neglect the "old" vaccines, including EEE and tetanus.

A veterinarian should be summoned at first sight of early clinical signs of encephalitic disease, especially in unvaccinated horses. A horse with EEE can portray varied neurologic signs in the early stages of the disease, including apparent blindness, loss of equilibrium, or a head tilt, or he can exhibit sudden behavior changes, lameness due to loss of coordination, or convulsions before progressing to recumbency, coma, and death. The Merck Veterinary Manual reports the mortality rate of EEE to be 50-90%.

For more information on WNV, watch the Webinar "Understanding West Nile Virus."

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care. She owns a portly gray gelding named Duncan and dabbles in several equestrian disciplines, with an emphasis on dressage.

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