Nov 14, 2023

California Horse Positive for WNV

A Quarter Horse mare in Kings County is positive for WNV and is currently alive.

Posted by Edited Press Release | Aug 4, 2023 | Article, EDCC Health Watch, Horse Industry News, Welfare and Industry


On July 31, a 4-year-old Quarter Horse are in Kings County, California, was confirmed positive for West Nile virus (WNV). She originally developed clinical signs on July 22, including ataxia, muscle fasciculations and hyperesthesia. She is currently affected and alive.

This is the second confirmed case of equine WNV in California this year.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

West Nile virus is transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:

West Nile virus has no cure. However, some horses can recover with supportive care. Equine mortality rates can reach 30-40%.

Studies have shown that vaccines can be effective WNV prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annually—one in the spring and another in the fall—in areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. It takes several weeks for horses to develop protection against the disease following complete vaccination or booster administration.

In addition to vaccinations, owners should work to reduce mosquito population and breeding areas and limit horses’ mosquito exposure by:


WNV 101