Wisconsin Confirms First Two Equine EEE Cases of 2012

Two horses have tested positive for Eastern equine encephalitis (EEE) a mosquito-borne illness caused by a virus that attacks the central nervous system, the Wisconsin Department of Agriculture, Trade and Consumer Protection announced yesterday (Aug. 21).

"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 State Veterinarian Robert Ehlenfeldt, DVM.

Blood samples were sent to the National Veterinary Services Laboratories in Ames, Iowa, on Aug. 17; the laboratory reported final positive results yesterday. The two horses were located in Clark and Lincoln counties in northern Wisconsin.

"Northern Wisconsin has good mosquito habitat and since it's been a wet summer up north the mosquito populations are high," Ehlenfeldt said. "We could see a lot more cases if we experience a long fall season."

Mosquitoes carry the disease from birds to horses. A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Its fatality rate in 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 of 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. Sixty equine EEE cases were confirmed in the United States in 2011, according to USDA Animal and Plant Health Inspection Service equine disease surveillance.

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 should be given at least annually and takes about four days to be effective. Vaccines will not protect horses that have already been infected when they receive the injections. Vaccines are available to protect against other strains of equine encephalitis along with EEE, and a separate West Nile virus vaccine is also available.

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

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