EHM in Pennsylvania Horses

The Equine Disease Communication Center (EDCC) reported Dec. 10 that, on Dec. 7, the Pennsylvania Veterinary Laboratory, in Harrisburg, confirmed equine herpesvirus myeloencephalopathy (EHM), the neurologic form of equine herpesvirus-1 (EHV-1) at a Snyder County facility.

The EDCC said one affected horse was exhibiting hind-limb ataxia (incoordination) and subsequently tested positive for EHV-1 (G-strain).

“As of Dec. 10, two horses were affected and both horses have been euthanized at this premises,” the EDCC said. “The premises, a pleasure horse barn in Snyder County, Pennsylvania, has been quarantined by the Pennsylvania Department of Agriculture Bureau of Animal Health.

“Eight horses remain on the premises and are being monitored for clinical signs of EHV-1 infection and biosecurity precautions have been implemented to prevent the spread of the virus off the premises. No additional clinical signs have been noted in the remaining horses.”

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 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.

EHM in Pennsylvania Horses

Horses with the neurologic form 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 present 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.