A 2-month old unvaccinated filly from Forest County is the first reported Wisconsin horse to have become infected with Eastern equine encephalitis (EEE) this year. The filly was euthanized on Aug. 23.

The Equine Disease Communication Center also reported a second case in Wisconsin, this one in a 4-year-old Welsh Pony mare from Vilas County with an uncertain vaccination history. The mare became acutely febrile, developed neurologic signs, and was euthanized after becoming recumbent (unable to rise), the EDCC said Aug. 31.

"Northern Wisconsin has good mosquito habitat,” said Julie McGwin, DVM, equine program veterinarian for the Wisconsin Department of Agriculture, Trade, and Consumer Protection. “It’s also been a very wet summer up north, which contributes to the problem.”

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. 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. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems