MADISON, Wis. – The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has confirmed that an unvaccinated 2-year-old gelding in Marathon County has tested positive for Eastern Equine Encephalitis (EEE). It is the state’s first confirmed case of EEE in a horse this year. DATCP has not had a reported case of EEE in Wisconsin since 2021, but cases have been reported in other states this year.
EEE and West Nile Virus (WNV) are viruses that can cause inflammation of the brain (encephalitis). Symptoms of EEE in horses include impaired vision, head pressing, circling, inability to swallow, lack of coordination, seizures, and death. Affected horses are often found down and unable to rise. EEE is fatal in up to 90% of horses showing signs of illness. Equine owners should contact their veterinarian if they observe any of these signs.
DATCP strongly encourages equine owners to speak with their veterinarians about vaccinating their horses for EEE. The American Association of Equine Practitioners recommends vaccinating for both EEE and WNV as part of the core vaccine protocol, meaning all horses should be vaccinated for these diseases. Adult horses that have never been vaccinated require two doses of the vaccine initially, followed by annual boosters.
EEE and WNV are not contagious between horses and do not pass directly between horses and people. Mosquitoes carry the viruses from infected birds, and the only route of transmission to humans or horses is through a mosquito bite. Confirmation of a horse infected with EEE means the virus is present in Wisconsin’s mosquito population.
Because the viruses follow mosquito populations, the threat in Wisconsin varies year-to-year depending on the weather and other factors. The highest risk in Wisconsin is generally mid- to late summer through the first killing frost. Vaccination is very effective at preventing both diseases and limiting exposure to mosquitoes will also help reduce risk. Follow the tips below to reduce exposure to mosquitoes:
- Remove items that could collect stagnant water (old tires, buckets, unused troughs, etc.)
- Keep rain gutters draining properly; turn wading pools and wheelbarrows upside down.
- Clean and chlorinate pools, outdoor saunas, and hot tubs; drain water from pool covers.
- Empty and replace water in birdbaths at least once a week.
- Consider keeping horses in the barn from dusk to dawn when mosquitoes are most active.
More information on EEE and WNV is available at https://datcp.wi.gov/Pages/
