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 monitoring.
Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM, the neurologic form.
The two most common forms of equine herpesvirus are EHV-1 and EHV-4. EHV-1 is the main cause of viral abortion outbreaks and can also result in fever or respiratory signs, which are sometimes followed by neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise). The neurological form, EHV myeloencephalopathy (EHM), is a result of damage to the central nervous system’s vasculature.
EHV-4 usually causes respiratory disease and occasionally can cause abortion or neurologic disease. It is most commonly seen—often in autumn and winter—in weaned foals and yearlings. Older horses with EHV-4 are more likely to spread the virus without showing clinical signs.
Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.