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Disease Alerts

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.

San Luis Obispo County, CA
Outbreak Identifier: 5527
Alert ID: 2917
February 27, 2023
Confirmed Case(s) - Official Quarantine

California Department of Food and Agriculture

Number Confirmed:
Number Exposed: 26 
Facility Type: Training Facility 
Age: 9; Gender: Mare; Breed: Quarter Horse (QH); Usage: Reining; Onset of Clinical Signs: 2/22/2023
Clinical Signs: Acutely recumbent and unable to rise, afebrile. Confirmation Date: 2/27/2023; Horse Status: Euthanized; Vaccination Status: Undervaccinated
Comments: A 9-year-old Quarter Horse mare in San Luis Obispo County displaying acute neurological signs was confirmed positive for Equine Herpesvirus Myeloencephalopathy (EHM) secondary to Equine Herpesvirus-1 on February 27th. She became acutely neurological on February 22nd, and was subsequently euthanized due to severity of clinical signs. The mare had recently attended a large western discipline event in Tarrant County, Texas from February 10 – 20th, with no clinical signs observed during the event or travel. Event management and Texas state animal health officials have been notified, and all horses attending this event are recommended to monitor temperatures twice daily for 14 days following their departure from the event grounds, and to contact their veterinarian with any concerns. Twenty-six (26) potentially exposed horses on the mare’s home premises have been quarantined, and CDFA was onsite for site assessment and assistance with implementation of enhanced biosecurity measures. CDFA will continue to actively monitor the situation. For more information and updates, go to

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