The New York State Department of Agriculture and Markets (NYSDAM) has confirmed 2011’s first case of Eastern equine encephalitis (EEE) in an Oneida County, N.Y., horse. The 9-year-old mare had lived at its current home for several years and had no recent travel history. The horse was unvaccinated. here is one other horse on the same premise that is not showing any signs of EEE, and that horse has since been vaccinated.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. The fatality rate for EEE in horses is 75-95%. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

Clinical signs for EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

Vaccines currently available drastically reduce the incidence of EEE in horses and are effective for six to 12 months, so horses should be vaccinated at least annually. In an area where the disease occurs frequently, most veterinarians recommend vaccination every six months. For the vaccine to be effective, it must be handled and administered properly and ideally 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 that the horse is vaccinated. While it’s best to have horses vaccinated well before potential exposure, vaccinating horses now will still provide protective benefits for this year’s mosquito season