The California Department of Food and Agriculture says the mare has been confirmed positive for the non-neuropathogenic strain of EHV-1, but her symptoms are unusually mild.
The infection can cause respiratory disease and the death of unborn foals. The virus is easily spread among horses, but humans cannot get it.
The horse was also shipped to the Springville Rodeo but did not compete there. She's now under quarantine and being monitored by the CDFA.
Concerned owners are encouraged to monitor their horses and report any temperature over 102 degrees to a veterinarian.