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

Contra Costa County, CA

Outbreak Identifier: 7603

Alert ID: 5179

August 28, 2026

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: 8/14/2026; Clinical Signs: ataxia, muscle fasciculations, weakness, hypersensitivity; Confirmation Date: 8/28/2026; Horse Status: Affected And Alive; Vaccination Status: Unvaccinated;

Comments: The eighth (8th) equine case of West Nile Virus in California in 2026 was confirmed in Contra Costa County. On August 28, 2026, a 2-year-old unvaccinated Quarter Horse mare in Contra Costa County displaying neurologic signs was confirmed positive for West Nile Virus. The mare is alive and recovering.;

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