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.



Contra Costa County, CA
Outbreak Identifier: 6064
Alert ID: 3513
December 04, 2023
Confirmed Case(s) - Official Quarantine

California Department of Food and Agriculture

Number Confirmed: 1; 
Number Exposed: 14; 

Horse 1: 
Age: 22; Gender: Mare; Breed: Quarter Horse (QH); Clinical Signs: neurologic, ataxic in hind end, fever, anorexia; Confirmation Date: 11/30/2023; Horse Status: Affected And Alive; 

Comments: A 22-year-old Quarter Horse mare from Contra Costa County displaying mild neurologic signs was confirmed positive for Equine Herpesvirus Myeloencephalopathy (EHM) secondary to Equine Herpesvirus-4 (EHV-4) on November 30th. The mare is alive and under veterinary care at an offsite veterinary hospital. Fourteen (14) potentially exposed horses at the home premises in Contra Costa County were quarantined on December 1st with enhanced biosecurity measures implemented. There has been no recent history of travel on or off these premises. CDFA was onsite, and will continue to actively monitor the situation.;