On Feb. 11, officials at the California Department of Food and Agriculture (CDFA) confirmed a horse at a Riverside County event facility with neurologic equine herpesvirus-1 (EHV-1), or equine herpesvirus myeloencephalopathy (EHM). The 12-year-old Zangersheide gelding began experiencing neurologic signs on Feb. 10.

The gelding is isolated at an equestrian event in Riverside County, at which two other horses that were stabled in the same barn on that premises—a 7-year-old Warmblood mare and a 7-year-old pony-cross mare, both experiencing fever only—have also been confirmed positive for EHV-1 and isolated. Forty-five other horses in the exposed barn are also under quarantine.

CDFA staff conducted a site assessment and is monitoring the premises after initiating enhanced biosecurity protocols including twice-daily temperature-taking and immediate isolation of suspected cases.

EHV 101

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 equine herpesvirus myeloencephalitis (EHM, the neurologic form).

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, 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) develop.

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.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.