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