California confirmed its 15th case of West Nile virus in a horse for 2026 on Tuesday, October 6, in an unvaccinated mare in Shasta County, according to a state alert posted on Friday, October 9. The state's West Nile virus website reports that virus activity is at a five-year high.
The California Department of Food and Agriculture (CDFA) reported the case through the Equine Disease Communication Center (EDCC). The horse, a 7-year-old Andalusian mare, showed neurologic signs, and the alert describes her as "alive and recovering."
In its update of Friday, October 9, California's West Nile virus website also counted 15 horses from 13 counties that had tested positive in 2026, and it listed one new horse case that week, from Shasta County.
Where the cases were
Ten of the 15 cases were in the counties below, according to CDFA alerts on the EDCC list, and all 10 of those horses showed neurologic signs. They appear in order of the dates given in the alerts:
- San Joaquin County, Wednesday, July 29: an unvaccinated 6-year-old Andalusian stallion, which was euthanized.
- Placer County, Friday, August 7: an unvaccinated 3-year-old Quarter Horse gelding.
- Contra Costa County, Friday, August 28: an unvaccinated 2-year-old Quarter Horse mare.
- Sacramento County, Thursday, September 3: a 3-year-old Oldenburg mare listed as "undervaccinated."
- Sutter County, Thursday, September 3: a vaccinated 10-year-old Paint gelding that lives in Contra Costa County but was exposed in Sutter.
- Amador County, Thursday, September 10: an unvaccinated 2-year-old Friesian stallion, which was euthanized.
- El Dorado County, Monday, September 14: an unvaccinated 9-year-old Warmblood mare.
- Shasta County, Tuesday, September 15: an unvaccinated 2-year-old Quarter Horse stallion.
- Amador County, Thursday, September 17: a vaccinated 5-year-old Quarter Horse gelding.
- Shasta County, Tuesday, October 6: the Andalusian mare described above.
The other five cases were in Stanislaus, Merced, Fresno, Kings and San Luis Obispo counties.
Vaccination status
Counted across all 15 alerts, seven horses were unvaccinated and two were listed as "undervaccinated." Three had been vaccinated, and three had no known vaccination history.
Three of the 15 horses were euthanized: the San Joaquin County and Amador County stallions listed above, and a horse in Kings County.
A five-year high statewide
The state's West Nile website carries a banner that reads "West Nile Virus Activity at Five-Year High." As of its Friday, October 9 update, the site counted 298 human cases in 24 counties in 2026, and 19 human deaths. It also reported 712 dead birds and 3,903 mosquito samples that had tested positive for the virus.
By comparison, California's fifth equine case of 2025 was confirmed on Monday, September 29, 2025, according to an EDCC alert from that year.
For horse owners
The CDFA alerts behind these figures appear on the EDCC's public alert list, which can be filtered to show California. Each alert names the county and describes the horse, including its vaccination status.
The state's West Nile website posts its counts for people, horses, dead birds and mosquito samples, along with the date of each update. Owners with questions about West Nile virus or vaccination can talk with their veterinarian.
From Saved by the Saddle
Saved by the Saddle runs free horsemanship programs for military veterans and at-promise youth at Ocean View Stables in Daly City, and is building R&R: Rescue and Rehab, its horse rescue program. No horse is in its care yet: a vet and farrier on call, a quiet space for a new horse, a written intake standard and funding for a decade or more of care come first.
Sources: Equine Disease Communication Center, Alert 5312, CDFA report of West Nile virus in Shasta County (October 9, 2026); California West Nile Virus Website, home page (updated October 9, 2026); Equine Disease Communication Center, alert list filtered to California (read October 9, 2026); Equine Disease Communication Center, Alert 4630, CDFA report of West Nile virus (September 2025)