Virginia’s first case of Eastern equine encephalitis (EEE) in a horse this year has been confirmed by the Virginia Department of Agriculture and Consumer Services (VDACS). The horse, a 2-year-old female draft cross from Chesapeake, was confirmed positive for EEE late in the afternoon of July 10. A veterinarian euthanized the horse prior to diagnosis on July 3, due to the severity of her clinical signs, which included incoordination, depression, and fever (105°F), progressing to an inability to stand without help.

This is the first reported case of EEE in a horse in Virginia this year. Last year the state had only one case, reported in September. So far there have been no reported cases of West Nile virus (WNV) in Virginia horses this year.

In an April 2009 press release, Richard Wilkes, DVM, state veterinarian, encouraged horse owners to work with their veterinarians to plan a vaccination schedule that would protect their horses from EEE. Available vaccines are effective in drastically reducing the incidence of both EEE and WNV in horses. The vaccines are effective for six to 12 months, so horses should be re-vaccinated at least annually. In an area where the disease occurs frequently, such as southeast and Tidewater Virginia, most veterinarians recommend vaccination every six months.

For the vaccine to be effective it must be handled and administered properly and be given at least two weeks before the horse is exposed to the virus. Additionally, to stimulate full immunity, horses must be vaccinated twice, about 30 days apart, the first year of vaccination. Generally, EEE is transmitted by mosquitoes. Other prevention methods include destroying standing water breeding sites for mosquitoes, using insect repellents, and removing animals from mosquito-infested areas during peak biting times, usually dusk to dawn