Multi-State West Nile Alert
West Nile Virus Cases Confirmed in Horses and Humans Across Three States
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Wisconsin officials said West Nile virus causes encephalitis and is fatal in 30% to 40% of horses that develop clinical signs. Reported symptoms can include loss of coordination, hind-end weakness, muscle tremors, teeth grinding, difficulty swallowing and inability to rise.
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Wisconsin’s agriculture department noted that mosquitoes acquire West Nile virus from infected birds, which serve as the virus’s natural reservoirs. The agency cited the American Association of Equine Practitioners’ recommendation that all horses receive core vaccinations for both West Nile virus and eastern equine encephalitis; previously unvaccinated adult horses initially require two doses followed by annual boosters.
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Cochise County health officials said most people infected with West Nile virus have no symptoms, while symptomatic illness may include fever, headache, body aches, joint pain, vomiting, diarrhea and rash. Severe disease can affect the nervous system and lead to confusion, paralysis, coma or death.
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The Cochise County report linked the heightened mosquito concern to unusually heavy summer rainfall and said dogs can become infected but only rarely develop fever, weakness or neurological symptoms.
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Michigan said testing costs for suspected animal cases may qualify for coverage through an MDARD arbovirus grant, with owners directed to contact the department at 800-292-3939 for information.
West Nile virus is spreading across the upper Midwest and Southwest this season. Michigan and Wisconsin have each confirmed their first horse cases of 2026, while Arizona's Cochise County reported two confirmed human cases and a probable third. Michigan MDARD and Wisconsin DATCP urged horse owners to vaccinate animals immediately, as mosquitoes remain active until the first hard frost.
The virus, spread only by infected mosquito bites, can cause serious neurological problems in horses and people. In horses, it triggers stumbling, weakness and difficulty standing. In humans, older adults and those with certain medical conditions face the highest risk of severe illness. Cochise County Health said most infected people show no symptoms at all.
Two Unvaccinated Horses Diagnosed in Upper Midwest
A three-year-old mare in Michigan's Missaukee County became the state's first confirmed domestic animal case in 2026. The unvaccinated horse is responding to treatment. Wisconsin's first case involved a six-year-old Quarter Horse mare in Brown County, also unvaccinated. Wisconsin agriculture officials emphasized that West Nile virus causes brain inflammation in horses and is fatal in 30% to 40% of animals that develop symptoms.
Infected horses show signs like loss of coordination, hind-end weakness, muscle tremors, teeth grinding and difficulty swallowing. Some cannot rise at all. Both states warned that mosquitoes carrying the virus stay active until temperatures drop below freezing, leaving a window of risk for months in some regions.
Vaccination and Prevention Critical for Horse Owners
Health officials are pushing all horse owners to vaccinate against West Nile virus and eastern equine encephalitis. The American Association of Equine Practitioners recommends that unvaccinated adult horses receive two initial doses, then annual boosters. Michigan said testing costs for suspected cases may be covered through an arbovirus grant. Owners can call 800-292-3939 for details.
Beyond vaccination, owners should eliminate standing water where mosquitoes breed, use approved insect repellents on animals, and limit outdoor time from dusk to dawn. Wisconsin officials noted that mosquitoes pick up the virus from infected birds, which are the virus's natural reservoir in the wild.
Arizona Reports Human Cases as Heat and Rain Spur Mosquitoes
Cochise County in southeastern Arizona has confirmed two human West Nile cases and identified a probable third. Cochise County health officials said most infected people have no symptoms. But symptomatic cases show fever, headache, body aches, joint pain, vomiting, diarrhea and rash. Severe infections can cause confusion, paralysis, coma or death.
The outbreak follows unusually heavy summer rainfall in the region, which created ideal breeding grounds for mosquitoes. Cochise County noted that dogs can catch West Nile virus but rarely develop fever, weakness or neurological problems. Older adults and people with chronic medical conditions face much greater risk of severe illness.
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