Two horses died of a severe, mosquito-borne disease in the Tomah area this week, according to the Wisconsin Veterinary Diagnostic Lab.
The Lab, housed at UW-Madison, discovered eastern equine encephalitis virus in the brain tissue of the horses, which were last vaccinated in the fall of 2016. The virus is deadly in horses about 90 percent of the time.
The disease can also be transmitted to humans, in rare cases. The virus, which is typically transmitted between birds, can be carried to and between horses and humans via mosquitoes. If a human contracts the virus, there is a 33 percent mortality rate, with a risk of significant brain damage in many survivors, according to the Centers for Disease Control and Prevention.
The spread of the virus is prompted by especially warm and humid weather. Last year, the virus infected 19 horses in 11 Wisconsin counties, according to the Department of Agriculture, Trade and Consumer Protection.
Keith Poulsen, a large animal veterinarian at the lab, recommends that horses be vaccinated in the spring, to prepare for mosquito season.
This is the second time in the past week that horses have died of mosquito-borne viruses - the Department of Agriculture, Trade and Consumer Protection announced Monday that a horse was euthanized in central Wisconsin after being infected with the West Nile Virus.