Outbreaks | Equine Disease Communication Center

Updates on current disease outbreaks are listed here as they occur and will include the date listed, disease name, location and current status. Specific premises will not be named but the general location by town, county and state will be listed. When locations, events or horses are at risk they will be listed. Updates will be posted as they are received.

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West Nile Virus

Stanislaus County, CA

Outbreak Identifier: 7076

Alert ID: 4596

September 18, 2025

Confirmed Case(s) - No Quarantine

Source: California Department of Food and Agriculture

Number Confirmed: 1;

Horse 1:
Age: 2; Gender: Mare; Breed: Quarter Horse (QH); Onset of Clinical Signs: 9/14/2025; Clinical Signs: ataxia (worse in front end), collapsing, leaning on wall, drooping ear; Confirmation Date: 9/18/2025; Horse Status: Affected And Alive; Vaccination Status: Vaccinated;

Comments: The third (3rd) case of West Nile Virus in California in 2025 was confirmed in Stanislaus County. On September 18, 2025, a vaccinated 2-year-old Quarter Horse mare in Stanislaus County displaying neurologic signs was confirmed positive for West Nile Virus. The mare is alive and recovering.;

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