The Equine Disease Communications Center reported in early March that a horse with the neurologic disease EHV-1 was euthanized at New Bolton Center in Kennett Square, PA. Other horses which were potentially exposed were being monitored. New Bolton Center’s clinical hospital operations have not been affected.
This case, and a horse being treated for EHV-1 in Ocala, FL are not related to the outbreak in Europe, which has shut down international competition in ten countries in Europe.
Equine herpesvirus 1 (EHV-1) or rhinopneumonitis is a contagious equine virus that can cause neurological disease, respiratory disease, newborn death and abortion. EHV-1 can be either neuropathic or nonneuropathic. Despite the names, both forms can cause neurologic disease.
Equine herpesvirus myeloencephalopathy (EHM) refers to the neurological form of EHV-1. Horses positive for EHV-1 that show neurological signs such as incoordination and hind-end weakness are considered positive for EHM. Once a horse is positive for EHM, other horses at the facility are at an increased risk of getting EHM. EHM is often fatal and those that make a rare recovery will likely face long-term neurologic problems.
On March 10, the Maryland Jockey Club alerted horsemen that four barns at Laurel Park had been placed under a fourteen-day quarantine due to equine herpesvirus. All horses at Laurel were required to stay on the grounds until further guidance, and horsemen were asked to take horses' temperatures twice daily and monitor them for signs of the disease.
On March 11 The New York State Department of Agriculture and Markets, Division of Animal Industry, confirmed two EHM and 2 EHV-1 cases at a stable in Brewster, NY. One of the four positive horses (an EHM case) competed at Old Salem Farm in North Salem, NY on March 5th and began exhibiting symptoms on March 7th. The other EHM case exhibited symptoms on Monday, March 8th. Old Salem Farm had no known cases of EHV-1 or EHM at this time. Show management is cleaning and disinfecting the facility and following appropriate EHV-1 biosecurity protocols.
This disease is caused by the EHV-1 virus which is common in the horse population and spread from horse to horse through contact with nasal discharge or as aerosol droplets. Horses can also contract the virus by coming into contact with contaminated surfaces such as stalls, water, feed, tack, and transport vehicles. Humans can spread the virus from horse to horse by contaminated hands and clothing.
EHM, the neurologic form, is not common and It is unknown why some horses develop the neurologic disease. Infected horses can shed the virus during the 5-6 day incubation period, even when showing no clinical signs. An estimated 40-60% of infected horses can become lifelong carriers of EHV-1. The virus can reoccur under periods of stress such as transport or a change in the horse’s environment.
Symptoms include nasal discharge, depression, incoordination, hind limb weakness, loss of tail or bladder tone, leaning against a fence or wall to maintain balance or inability to rise.
There is no cure for EHM. Supportive care includes the use of NSAID drugs. The prognosis for horses showing neurological signs is often poor with mortality as high as 30 percent. Currently, there is no USDA licensed EHV-1 vaccine proven to protect against the neurological disease. The best method of protection is always to maintain current EHV vaccinations on all horses on your property and to follow correct biosecurity protocol when bringing new horses onto your premises, when traveling, or during any activity where horses may come together. Proper biosecurity measures include extensive cleaning and disinfection of surfaces and equipment. Individuals treating or coming into contact with infected horses need to follow appropriate disinfection protocols when handling multiple horses.