California Pony Tests Positive for EHV-1
Officials at the California Department of Food and Agriculture (CDFA) confirmed on March 14 that a 14-year-old pony mare in Alameda County tested positive for equine herpesvirus-1 (EHV-1). On March 12 the mare presented with neurologic signs, including acute blindness, cranial nerve deficit, decreased tail and tongue tone, and hypermetria (a condition of cerebellar dysfunction in which voluntary muscular movements tend to result in the movement of bodily parts short of the intended goal). She’s reported as having been vaccinated and as affected and alive under quarantine at a veterinary hospital.

Forty-four additional horses were exposed and are quarantined at the home premises under enhanced biosecurity, including twice-daily temperature monitoring. All potentially exposed horses have been traced and owners contacted. Any horse that displays clinical signs or a temperature exceeding 101.5°F will be reported to the veterinarian for evaluation and potential blood and nasal swab sampling.

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.