The number of confirmed Eastern equine encephalitis cases (EEE) in horses has risen to 44 as of May 6 in north central Florida, according to Bill Jeter, DVM, diagnostic veterinary manager for Florida’s Division of Animal Industry. This confirmed earlier speculations that 2003 will have higher-than-normal numbers of EEE cases this year. The virus has been confirmed in 18 counties, and 24 of the 44 cases are in six adjacent counties (Alachua–4, Baker–2, Bradford–3, Gilchrist–7, Levy–4, and Marion–4).

Jeter said that only seven of the affected horses have survived. “In Florida, (EEE) has always been pretty virulent and severe, with a 90-93% mortality rate,” he said.

EEE is caused by a virus found in wild birds, and it is transmitted to horses and humans via the bite of an infected mosquito. Horses do not develop high enough levels of the EEE virus in their blood to be contagious to other animals or humans.

Onset of clinical signs in the affected horses has been rapid and severe. Jeter said, “By the time the vet sees the horse, it already has pretty severe neurologic signs of staggering around and continuous walking, head pressing, a dummy-like stance, and a few have shown muscle fasciculations (trembling),” a distinguishing neurologic sign often associated with West Nile virus (WNV). Jeter said that typically, horses with EEE show fevers from 103-106°F, while WNV-associated fevers are lower. “Usually we don’t get that high of a fever with WNV, and it’s not quite as progressive (in the clinical signs). Usually by the time (EEE cases) are recumbent and paddling, the vets must put them down