Equine Herpes Virus-1

EHV-1 2011  Information

We understand that there was a high level of concern regarding reports of an outbreak of EHV-1 (neurologic herpes) in May 2011 and how it may affect horses in Arizona. This outbreak is reported to have started at a NCHA cutting show in Ogden, Utah which was attended by horses from many western states. There were several  confirmed cases of EHV-1 in most of the Western States including Arizona. Every affected horse was at the cutting horse show in Ogden, Utah, or horses directly exposed to those horses at that show.

At that time, we were recommending that anyone who suspects that their horse may have been exposed to the virus take their horses temperature twice daily and notify our clinic at 623-386-2928 if their horse has a fever of over 102. We also ask that you call if your horse shows respiratory signs (cough, nasal discharge) or any neurological sign. We were recommending limiting travel to necessary travel only and minimizing your horses exposure to other horses as much as possible. At that time, we were taking temperatures on horses coming to the clinic as a precaution. Below is a statement that was issued by the American Association of Equine Practitioners (AAEP) regarding the previous  EHV-1 situation. Further information can be obtained by visiting the AAEP website at aaep.org

 There were 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. At this time control of the outbreak is critically dependent on biosecurity.  Laboratory submission of nasal swabs and whole blood samples collected from the exposed horse can be utilized for virus detection and isolation. Please consider testing any suspected cases.

The EHV-1 organism spreads quickly from horse to horse but typically only causes neurological disease sporadically. However, in an outbreak of EHV-1 neurologic such as we are experiencing now, the disease can reach high morbidity and case fatality rates. The incubation period of EHV-1 infection is typically 1-2-days, with clinical signs of fever then occurring, often in a biphasic fever, over the following 10 days. When neurological disease occurs it is typically 8-12 days after the primary infection, starting often after the second fever spike. 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, although antiviral drugs (i.e. valacyclovire) may have some value before neurological signs occur. Non-specific treatment may include intravenous fluids, and other appropriate supportive therapy; the use of anti-inflammatory drugs (NSAIDs) is strongly recommended. 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 infection 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.

At this time, there have been no new cases of EHV-1 since May 2011 and the outbreak has been contained. Travel restrictions have been removed and there is no longer a high risk in this state.