Wisconsin Horse Tests Positive for EEE

Wisconsin Horse Tests Positive for EEE

Eastern equine encephalitis is a mosquito-borne illness caused by a virus that attacks the horse's central nervous system.

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A horse in Dunn County, Wisc., has tested positive for Eastern equine encephalitis (EEE), and two alpacas, also in Dunn County, have died as a result of the disease. Eastern equine encephalitis is a mosquito-borne illness caused by a virus that attacks the central nervous system.

"Horse owners who have not already had their animals vaccinated this year for EEE and other mosquito-borne diseases should take this as a warning, and those who have vaccinated should check with their veterinarians to see whether a booster is indicated," said Wisconsin State Veterinarian Robert Ehlenfeldt, DVM. There is no approved vaccine for alpacas. Alpaca owners should consult their veterinarians about preventive measures, he said.

Blood from the affected animals were sent to the University of Minnesota Veterinary Diagnostic Laboratory July 9. Initial positive results there were confirmed by the Pennsylvania Animal Diagnostic Laboratory System, which reported final positive results Aug. 9.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. The fatality rate for EEE-affected 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.

Wisconsin experienced a major EEE outbreak in 2001 with 69 confirmed or presumptive positive cases, mostly in the northwestern part of the state. Since then, sporadic cases have occurred. Because EEE follows mosquito populations, the disease normally occurs beginning in mid- to late summer and remains a threat until the first killing frost.

Horses that have never been vaccinated will need two doses two to four weeks apart, and the vaccine will take at least two weeks to build up enough antibodies to protect them. A booster would normally be only one dose and would take about four days to be effective. Vaccines will not protect horses that have already been infected when they receive the injections. Vaccines are available that protect against other strains of equine encephalitis along with EEE, and a separate West Nile virus vaccine is also available.

"Northern Wisconsin has good mosquito habitat, and that has been where we've seen most cases of EEE over the years," Ehlenfeldt said. "It's been a wet summer up north, and mosquito populations are really high. If we get a good long fall, we could see a lot more cases."

In addition to vaccination, owners can take steps to reduce their animals' exposure to mosquitoes. They should eliminate standing water by removing objects such as old tires or even the folds in tarps where water collects and changing water frequently in water troughs, bird baths, and similar containers. If possible, owners should also keep their animals inside barns from dusk through dawn, when mosquitoes are most active.

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