The number of confirmed Eastern equine encephalitis cases in horses has risen to 23 in north central Florida, said Dr. Bill Jeter, diagnostic veterinary manager for Florida's Division of Animal Industry. The numbers confirm earlier speculation that 2003 would have higher-than-normal incidences of EEE.
The virus has been confirmed in 12 Florida counties, and 14 of the 23 cases are in five contiguous counties. Gilchrist County has had the greatest concentration of cases with five.
Jeter said only one of the affected horses 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 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 EEE horses has been rapid and severe. "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 (trembling)," Jeter said.
Jeter said he's surprised there haven't been any reported human cases, because a rash of horse cases usually precedes human cases.
It's difficult to estimate how many Florida horses are properly vaccinated for EEE since the vaccine is available over the counter and can't be tracked as easily as the West Nile virus vaccination, which is only available through veterinarians.
Jeter said while the number of cases being detected is leveling off and is not as high as earlier in April, there are still a very significant number of cases. "Probably for every one horse that we get confirmed, there are two or three that were not reported," he said.