Seven new equine West Nile virus (WNV) cases have been reported in different states and shared by the Equine Disease Communication Center.
Pennsylvania
- Dauphin County: One horse tested positive.
- Lancaster County: One horse tested positive.
- Union County: One horse tested positive.
Tennessee
- McMinn County: One horse tested positive.
Michigan
- Kent County: One unvaccinated horse tested positive.
- Muskegon County: One unvaccinated horse tested positive.
California
- Amador County: A vaccinated Quarter Horse gelding tested positive on Sept. 17 after showing neurologic signs. The horse is currently recovering. This case marks California’s 14th confirmed equine WNV case in 2026.
The Equine Disease Communication Center (EDCC) provides verified equine disease reports through the EDCC Health Watch program. EDCC is an independent nonprofit organization supported by industry donations to offer open access to infectious disease information.
WNV 101
West Nile virus is transmitted to horses via infected mosquito bites. Clinical signs in infected horses may include flu-like symptoms, muscle twitching, hypersensitivity, changes in mental activity, drowsiness, and weakness. West Nile virus has no cure, and mortality rates in horses can be as high as 30-40%.
Vaccination is a key prevention method for WNV. Horses should receive annual booster shots, with some veterinarians recommending bi-annual boosters in areas with extended mosquito seasons. Unvaccinated horses require a two-shot vaccination series. It takes several weeks for horses to develop immunity after vaccination.
In addition to vaccination, owners can reduce mosquito exposure by eliminating stagnant water sources, regularly cleaning water containers, keeping horses indoors during peak mosquito activity times, and using approved mosquito repellents for horses.