The Sconi

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has confirmed that a three-year-old Quarter Horse stallion in Grant County has tested positive for West Nile Virus (WNV). This marks the first confirmed case of WNV in a horse in Wisconsin for 2025. Last year, there were nine documented cases of WNV in horses within the state.

West Nile Virus is known to cause inflammation of the brain, also referred to as encephalitis, in both horses and people. In horses, symptoms can include fever, loss of coordination, hind-end weakness, depression, loss of appetite, muscle tremors, teeth grinding, difficulty swallowing, head pressing, excessive sweating, and sometimes inability to stand. According to DATCP, “The disease can cause brain inflammation in horses and people, and it is fatal in 30-40% of horses showing signs of illness.”

The virus is not transmitted directly between humans and horses. Mosquitoes are responsible for spreading WNV by carrying it from birds—natural reservoirs for the virus—to other species through bites. The risk period for transmission is typically highest from mid to late summer until the arrival of the first killing frost.

In addition to animal cases this year, the Wisconsin Department of Health Services recently confirmed its first human infection with West Nile Virus for 2025. So far this year five human cases have been reported in Wisconsin. These findings indicate that mosquitoes capable of transmitting WNV are present throughout the state.

To help protect equine populations from these risks, experts recommend vaccination as a primary preventive measure. The American Association of Equine Practitioners (AAEP) advises including vaccinations against both West Nile Virus and Eastern Equine Encephalitis as part of a horse’s core vaccine protocol. Horses that have never received these vaccines should get two initial doses followed by annual boosters.

Beyond vaccination efforts, DATCP provides additional recommendations aimed at reducing mosquito exposure around stables and pastures:

- Remove any items where stagnant water might collect such as old tires or unused troughs.

- Ensure rain gutters function properly; turn over wading pools and wheelbarrows when not in use.

- Clean and chlorinate outdoor pools or hot tubs regularly; drain water from pool covers.

- Change birdbath water at least once per week.

- Consider keeping horses indoors from dusk until dawn when mosquitoes are most active.

For more detailed guidance on preventing West Nile Virus and related diseases in horses—including up-to-date resources on prevention strategies—visit https://datcp.wi.gov/Pages/Programs_Services/HorsesEEEWNV.aspx .

“While people can be infected by WNV, the virus does not pass directly between humans and horses. The only route of transmission is from a mosquito bite,” stated DATCP officials.

“Mosquitoes transmit the virus from birds, which serve as natural reservoirs for WNV. Since humans and equines get WNV from mosquitoes, the threat is normally highest when mosquitoes are most active,” DATCP added.

“The American Association of Equine Practitioners (AAEP) recommends vaccinating for both WNV and Eastern Equine Encephalitis as part of the core vaccine protocol,” according to advice provided by DATCP.

Horse owners seeking more information about symptoms or prevention methods are encouraged to consult their veterinarians or visit official resources online.