The first equine case of West Nile virus (WNV) in the United States this year has been confirmed in a Florida horse. The horse was located in Jefferson County, Florida, where WNV-positive crows were found in June. The United States Department of Agriculture’s Animal and Plant Health Inspection Service confirmed the results July 21 at its National Veterinary Services Laboratory (NVSL) in Ames, Iowa.

WNV was first recognized in the Western Hemisphere in 1999, concentrated mainly in New England in horses and humans. The disease is spread by the bite of an infected mosquito. Since then, the virus has overwintered in mosquitoes and returned with intensity, found in dead birds as far south as North Carolina and as far west as Erie County, Pennsylvania in 2000, and in dead birds in Florida and Georgia this year. Historically, the earliest onset of clinical equine cases was August 17, 2000, in Staten Island, N.Y, and equine cases of WNV were never reported south of Delaware. Therefore, the discovery of WNV in horses in Florida this early in the year was an unexpected occurrence.

The affected horse was an adult male euthanized on or about July 12. Serum and brain samples were collected prior to death and sent to the Florida Department of Agriculture and Consumer Services’ laboratory in Kissimmee, Fla. The samples were forwarded immediately to NVSL for further testing and confirmation.

“We are being faced with a challenge of controlling the mosquitoes that carry this new virus,” said Florida’s Commissioner of Agriculture, Charles Bronson. Bronson explained that WNV is maintained in the wild bird population, and normal bird migration routes likely brought the disease south. “We will be just as vigilant in our disease surveillance and mosquito control efforts for all Florida as we are responding to this outbreak in North Florida