The Maryland Department of Agriculture (MDA) received confirmation yesterday (April 5) that equine herpesvirus type-1 (EHV-1) was the cause of equine illness at the Columbia Horse Center in Columbia, Md. The virus, which causes upper respiratory infection, can also cause neurologic disease. Three horses experienced neurologic signs before their conditions required euthanasia. Two other horses in nearby stalls that showed signs of mild neurologic illness are doing well, and no additional horses are showing any clinical signs.

“We are relieved to have a definitive diagnosis and that no additional horses are showing signs of illness,” said James I. Fearer, DVM, acting state veterinarian for Maryland. The results were received from a laboratory at the University of Pennsylvania’s New Bolton Center on Tuesday (April 5). “All parties involved have made the assumption from the start that this could be an infectious or contagious disease of horses, so we will not have to change our protocols in any way and the measures appear to have prevented any spread of the virus. However, precautionary measures on the farm will remain in place until we are certain that the incident is concluded.” 

There is currently no known method to reliably prevent the neurologic form of EHV-1 infection. It is recommended to maintain appropriate vaccination protocols in an attempt to reduce the incidence of the respiratory form of EHV-1 infection, which might help prevent the neurologic form. Transmission of the virus can occur via coughing or sneezing over a distance of up to 35 feet, as well as by direct contact with infected horses, feed, and equipment. 

“It is important to note that all of the horses had current vaccinations and that the incidence of the illness is no fault of the owners or facility managers,” said Fearer. “Why the neurologic form of EHV-1 occurs occasionally is not yet known