BROWN COUNTY, Wis. (CBS 58) -- An unvaccinated 6-year-old Quarter Horse mare in Brown County has tested positive for West Nile Virus, marking the state's first confirmed equine case this year, the Wisconsin Department of Agriculture, Trade and Consumer Protection announced on Tuesday, Sept. 15.

The virus can cause brain inflammation in horses, with symptoms including fever, loss of coordination, muscle tremors and an inability to rise. It is fatal in 30% to 40% of horses that show signs of illness, according to DATCP.

The department documented five equine cases statewide in 2025, and the virus spreads only through mosquito bites and does not pass directly between horses and people, according to DATCP.

DATCP is encouraging horse owners to talk to their veterinarians about vaccination, along with reducing standing water and other mosquito breeding sites around their property.

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