Equine Herpes Concerns

Currently, there are reports of equine herpes virus myeloencephalopathy (EHM) affecting an unconfirmed number of horses in the U.S. and Canada. This outbreak appears related to initial cases at a cutting horse show in Ogden, Utah, which was held from April 29 - May 8. Horses at that event may have been exposed to this virus and subsequently spread the infection to other horses. While the true extent of this disease outbreak is uncertain, there is clearly a very significant elevated risk of EHM cases at this time.

If you were at this show, contact your vet right away.

Although there are no confirmed cases in Arizona, there are some strong suspects throughout our state.

At this time, control of the outbreak is critically dependent on biosecurity.
Horse shows are being cancelled to prevent the spread.

We recommend that you keep your horses where they are until we have more information. This includes trail riding.
If you own a barn, we recommend not allowing horses to move on or off your property.

The USDA encourages owners to monitor their horses for clinical signs of disease. A rectal temperature in excess of 102F commonly precedes other clinical signs and they are urging owners to take temperatures twice a day. If temperatures are above 102F, owners are urged to contact their veterinarians. Laboratory submission of nasal swabs and blood samples collected from the exposed horse can be utilized for virus detection and isolation.

The EHV-1 organism spreads quickly from horse to horse and the neurologic form of the virus can reach high morbidity and mortality rates. The incubation period of EHV-1 is typically 2-10 days. In horses infected with the neurologic strain of EHV-1, clinical signs may include: nasal discharge, incoordination, hind-end weakness, recumbency, lethargy, urine dribbling and diminished tail tone. Prognosis depends on severity of signs and the period of recumbency. There is no specific treatment for EHV-1 but it could include intravenous fluids and anti-inflammatory drugs. Currently there is no equine vaccine that has a label claim for protection against the neurological strain of the virus.

Horse-to-horse contact, aerosol transmission and contaminated hands, equipment, tack and feed all play a role in disease spread. However, horses with severe clinical signs of neurological EHV-1 illness are thought to have large viral loads in their blood and nasal secretions and, therefore, present the greatest danger for spreading the disease. Immediate separation and isolation of identified suspect cases and implementation of appropriate biosecurity measures are key elements for disease control.