Officials at the California Department of Food and Agriculture (CDFA) confirmed a yearling Quarter Horse filly with neurologic equine herpesvirus-4 (EHV-4) on Aug. 3. The filly, who had been vaccinated, began experiencing acute neurologic signs including severe bilateral (both sides) pelvic limb rigidity and fever on July 28 and was subsequently euthanized.

The filly had attended an Imperial County event on July 18-19. Event management was notified, as were show participants, who were advised to monitor their horses’ temperatures twice a day. No additional cases have been identified.

The case is classified as suspect equine herpesvirus myeloencephalitis (EHM) because veterinarians could not identify any other cause of the filly’s neurologic signs.

Officials quarantined the filly’s home premises, where three exposed horses are under enhanced biosecurity protocols and twice-daily temperature