By Blake Jackson
The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has confirmed the state’s first equine case of West Nile Virus (WNV) this year.
The case involves an unvaccinated three-year-old Quarter Horse stallion in Grant County. In 2024, nine equine cases were recorded across the state, according to DATCP’s case map.
WNV is a mosquito-borne disease that can lead to encephalitis, or brain inflammation, in both horses and people. In horses, symptoms may include fever, poor coordination, weakness in the hindquarters, loss of appetite, muscle tremors, depression, excessive sweating, teeth grinding, difficulty swallowing, head pressing, or collapse with inability to rise. The disease can be fatal in 30-40% of infected horses that show clinical signs.
Humans cannot contract WNV directly from horses, nor can horses transmit it among themselves. The virus is spread exclusively through mosquito bites, with birds serving as the primary carriers.
Risk of infection is highest in mid-to-late summer and continues until the first hard frost. Wisconsin’s Department of Health Services recently confirmed the first human case of WNV in 2025, bringing the state’s total to five so far this year.
DATCP urges horse owners to work with veterinarians to ensure their animals are properly vaccinated. The American Association of Equine Practitioners (AAEP) includes WNV and Eastern Equine Encephalitis in its list of core vaccines recommended for all horses. Horses with no prior vaccination history need two initial doses followed by yearly boosters.
Alongside vaccination, mosquito control is an important prevention strategy. DATCP recommends eliminating standing water in containers such as tires, buckets, and unused troughs; maintaining clean rain gutters; turning over wading pools and wheelbarrows; cleaning and chlorinating outdoor pools and hot tubs; refreshing birdbath water weekly; and housing horses indoors from dusk to dawn when mosquito activity peaks.
For additional information on WNV and equine health guidance, visit DATCP’s website at: datcp.wi.gov.
Photo Credit: gettyimages-patrick-jennings
Categories: Wisconsin, Livestock