Three new equine cases of West Nile virus (WNV) have been reported to the Equine Disease Communication Center.
In Tennessee, one horse in Knox County and one horse in Washington County tested positive for WNV.
In California, an 8-year-old Quarter Horse gelding in Siskiyou County tested positive for WNV on Oct. 8. The horse is currently alive and recovering, making this California’s 16th confirmed equine case of 2026.
EDCC Health Watch is a marketing program by Equine Network that utilizes information from the Equine Disease Communication Center (EDCC) to create and distribute verified equine disease reports. The EDCC is an independent nonprofit organization supported by industry donations to provide open access to infectious disease information.
WNV 101
West Nile virus is transmitted to horses through bites from infected mosquitoes. Clinical signs of WNV in horses may include:
- Flulike symptoms, such as mild anorexia and depression
- Muscle and skin twitching
- Hypersensitivity to touch and sound
- Changes in behavior or mentation
- Occasional drowsiness
- Difficulty walking or moving
- Weakness or ataxia
There is no cure for WNV in horses, and mortality rates can be as high as 30-40%. Vaccination has been shown to be an effective prevention method for WNV. Horses should receive annual booster shots, with some veterinarians recommending two boosters per year in areas with extended mosquito seasons. Unvaccinated horses may need a two-shot vaccination series over a few weeks to build immunity.
In addition to vaccination, horse owners should take steps to reduce mosquito populations and limit exposure, such as eliminating stagnant water sources, cleaning water containers regularly, keeping animals indoors during peak mosquito activity times, and using approved mosquito repellents for horses.