Tuesday, May 17, 2011

EHV-1 Outbreak in the Western US and Canada

Tuesday May 17 2011

An outbreak of neurologic Equine Herpes Virus (EHV-1) started at the NCHA Western National Championships in Ogden, Utah which took place on April 28-May 8. Horses had left the event before participants were notified of the disease.

It is highly contagious and any exposed horses and facilities must be quarantined to stop the spread of the disease. It could become very serious.

Thehorse.com defines EHV-1: Equine herpesvirus is highly contagious and can cause a variety of ailments in horses, including rhinopneumonitis (a respiratory disease mostly of young horses), abortion in broodmares, and myeloencephalopathy (evident in the neurologic form). The virus is not transmissible to humans. Clinical signs of the neurologic EHV-1 form include fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. The virus is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions.

As of today, May 17, "The number of horses confirmed or suspected to have EHV-1 remains on the rise, with several states reporting cases," according to Thehorse.com.

So far there have been 6 EHV-1 positive horses in California, 2 in Colorado (one was euthanized; a second horse was euthanized after displaying severe signs although a positive diagnosis has not been confirmed), 1 in Washington.

The AAEP released the following information:

Currently, there are numerous reports of equine herpesvirus myeloencephalopathy (EHM) affecting horses and farms across 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. In order to assist you and your clients further, visit online here http://list.aaep.org/t/68400/2510/113322/0/ for Frequently Asked Questions, resource information from the AAEP, USDA, state and provincial animal health departments, and other related information regarding this outbreak and the disease. For additional questions, please contact Keith Kleine, AAEP director of industry relations, at (800) 443-0177 or kkleine@aaep.org.


William Moyer, DVM
2011 AAEP President
Raising the Standard in Horse Health

American Association of Equine Practitioners
4075 Iron Works Parkway
Lexington , KY 40511


Remember the devastating Equine Influenza in Australia in 2007? It's better to be overly cautious than to risk a severe outbreak, as there is no vaccination, the disease is easily transmissible, highly contagious, and can be deadly.

It is recommended all horse owners follow these four biosecurity measures on their operations:

* require individuals to wash their hands before and after contact with each horse;
* avoid contact with other horses;
* disinfect boots and change clothes that come into contact with other people’s horses;
* isolate horses returning from shows for 2-3 weeks.

If you have any reason at all to think your horses could have been exposed, monitor your horses for any symptoms, check for elevated temperatures (above 102) twice daily, hunker down for a week or so, and contact your veterinarian immediately if you see any symptoms (fever, ataxia - incoordination, weakness or paralysis of the hind limbs, and incontinence).

Equisearch has good up-to-date information on the disease, its progress and monitoring:
http://blogs.equisearch.com/horsehealth/?utm_source=eqs&utm_medium=nl&utm_campaign=eqs .

TheHorse.com will have reliable information:


  1. I hadn't heard about this, so I'm grateful to know. We'll probably steer clear of other horses for awhile.

  2. Good information. Our trainer had a horse at the Utah show and has canceled all lessons and clinics for 10 days - I guess they were told that's the incubation period.

  3. I'm pretty far east, but still staying on top of this. Very scary indeed!

  4. Always a worry. Thanks for the information.

  5. Grave problema, pero con los aislamientos y cuarentenas, esperemos que no tengais bajas no deseadas de la cabaña equina.
    Que vuestros caballos se vean sanos y fuertes para competir en las pruebas de Resistencia Ecuestre.
    Saludos de Gabriel desde España.

  6. We just got notified that the 'Ride the Divide' endurance ride in New Mexico has been cancelled because of the outbreak. Better safe than sorry.

  7. Thanks for sharing the info - very valuable to all