23 Florida EEE Cases

The number of confirmed Eastern equine encephalitis cases (EEE) in horses has risen to 23 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 12 counties, and 14 of the 23 cases are in five counties that are adjacent. Gilchrist County has had the greatest concentration of cases with five cases.


Jeter said that only one of the affected horses has 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 EEE 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.”

EEE cases “show more severe neurologic symptoms related to brain and spinal cord damage” than horses with WNV, explained Jeter. EEE horses “have no response to typical medications given for West Nile virus like Banamine or steroids. They’re usually non-responsive.”

“In all of them, basically their vaccination history is sketchy or there has been no vaccination,” said Jeter. “We have to try and keep reminding people to vaccinate the horses and take as many precautions as possible with themselves.”

Jeter was surprised that 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 WNV vaccination, which is only available through veterinarians. “We’ve been preaching that they should vaccinate three times a year for Eastern because we have virus exposure on a year-round basis,” he explained.

The number of cases tallied so far in 2003 is significant since the latter part of May or early June is when EEE cases usually start appearing. The 2002 case total was 25 horses. Out of the 23 cases confirmed so far in 2003, at least 20 of them had March onset dates. “We’re way ahead of schedule this year,” said Jeter.

“We still have a lot more submissions coming every day (to the Kissimmee Diagnostic State Laboratory),” he said. “This will bring up this number by early next week into the 30s. I was looking for a spike and then a drop off (in number of cases), then a sporadic case here or there.”

He said that while the number of cases being detected is leveling off and is not as high as earlier this month, 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.”

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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