In many horses, fever is the only sign of EHV-1 infection, which can go undetected. | Photo by Alexandra Beckstett/The Horse

The University of Pennsylvania School of Veterinary Medicine’s New Bolton Center, in Kennett Square, is under a self-imposed quarantine after a horse there tested positive for equine herpes myeloencephalitis (EHM).

New Bolton Center has canceled all elective equine appointments pending further instructions from the regional state veterinarian.

New Bolton Center will receive emergency equine or camelid (also susceptible to equine herpesvirus-1 or EHV-1) admissions only during this time. All cows, goats, sheep, or pig patients can be admitted and discharged without restriction. Field service operations are unaffected and the center will continue to receive appointments for non-equine animals. Reproductive services at the Hofmann Center are fully operational.

On Jan. 16, a horse recently admitted to the hospital for non-neurologic signs tested positive for EHV-1 and ultimately displayed signs compatible with EHM. Of particular relevance to the larger equine community, this horse had a non-traditional presentation for EHM, including a low-grade fever and several days of normal temperature prior to developing neurologic signs.

The New Bolton Center is working with the Pennsylvania Department of Agriculture to contain any possible spread of the infection and to determine the duration of the quarantine. Owners and referring veterinarians of the horses still at New Bolton are being notified and biosecurity measures have been implemented to protect hospitalized horses.

Equine herpes myeloencephalitis is the neurologic disease caused by EHV-1. Many horses are latently infected making prevention difficult, but the virus does not persist for long in the environment and is sensitive to common disinfectants. The disease does not affect humans or ruminants, but can negatively impact camelids.

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 myeloencephalopathy (the neurologic form). In many horses, fever is the only sign of EHV-1 infection, 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 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.