The New York State Department of Agriculture and Markets, Division of Animal Industry, has confirmed two horses with EHV-1 and two horses with EHM, the neurologic form of the disease. All four horses are currently quarantined at a stable in Brewster. Their home facility has implemented strict biosecurity measures and temperature monitoring in cooperation with the state. The disease’s origin is unknown and under investigation, according to the state.

One of the four positive horses (an EHM case) competed at Old Salem Farm in North Salem, New York. This horse arrived on the evening of Thursday, March 4, competed in equitation on March 5, and returned home that day. The horse started to exhibit symptoms on Sunday, March 7.

The other EHM case exhibited symptoms on Monday, March 8. Veterinarians sampled the two additional EHV-1 cases due to their proximity to the index case.

Old Salem Farm currently has no known EHV-1 or EHM cases. Show management is cleaning and disinfecting the facility and following appropriate EHV-1 biosecurity protocols, according to the state’s report.

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.