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Horse Owners Urged to Be Vigilant in the Face of Equine Herpes Outbreak

Statement by The Humane Society of the United States and the Humane Society Veterinary Medical Association

An outbreak of Equine Herpesvirus Myeloencephalopathy (EHM), a severe neurological disease caused by the highly contagious Equine Herpesvirus Type 1 (EHV-1), recently struck horses in the western region of the United States and Canada. In addition to infecting equine species such as horses, mules and donkeys, EHV-1 may infect some camelids, including llamas and alpacas.

The initial cases of EHM arose in horses who attended a championship competition of the National Cutting Horse Association in Ogden, UT, April 29 through May 8. So far, confirmed cases have been reported in eight states (California, Colorado, Idaho, New Mexico, Oregon, Texas, Utah and Washington), although horses from a total of 18 states attended the event, where they were all potentially exposed to the virus.

Background Information on EHM and EHV-1

Equine experts say EHV-1 is not a new virus; it is endemic in horse populations around the world. It can cause upper respiratory infections, and abortions in pregnant mares. EHM is the most infrequent, but potentially devastating, form of EHV-1 infection, causing severe neurological abnormalities. EHM symptoms often begin with nasal discharge, lethargy and a fever and can progress to incoordination (including leaning against walls or fences to maintain balance), weakness or paralysis of the hind limbs, swelling of the lower limbs, urinary incontinence, inability to urinate (in these cases bladder rupture is a significant risk) or defecate, loss of tail tone, an inability to rise, and it can also result in death.

Many horses develop latent EHV infections. That is, they may not display any symptoms themselves, but they can actively infect other horses. The EHV-1 incubation period (from time of exposure) is typically 4-6 days but can be longer. Fever and other symptoms may occur over the next 10 days. EHM, the neurological form of the disease, generally occurs 8-12 days after the primary infection. It is important to note that horses may continue to shed the virus up to 21 days after their symptoms subside.

The EHV-1 virus can be transmitted by both direct and indirect contact with infected horses. Transmission can occur directly from horse to horse through close contact, primarily with infected nasal secretions, or via aerosolization of secretions at close range. Infection can also be spread indirectly via contaminated water buckets, feed tubs, tack, grooming equipment and supplies, and even by contaminated human hands, clothing or shoes. For these reasons, horse owners should employ sound barn hygiene and proper biosecurity practices at all times. All areas and items to which the virus may have spread should be thoroughly disinfected.

Precautions Urged for Horse Owners

We encourage horse owners to be vigilant in observing their horses for early signs of illness. If you suspect or observe any symptoms, immediately isolate the horse(s) and limit movement of any horses on and off your premises. Then contact your local equine veterinarian, and seek advice concerning diagnosis. It is important to distinguish EHM from other neurological diseases with similar symptoms, such as rabies, Equine Protozoal Myeloencephalitis (EPM) and West Nile virus. EHV infections can be confirmed by testing equine nasal swabs or blood samples. In addition to diagnosis, veterinarians can help horse owners design quarantine and treatment regimens, along with comprehensive disease prevention protocols, including barn hygiene guidelines. No vaccine is currently labeled to provide protection against EHM.

Although EHM is a potentially life-threatening disease, it is not necessarily a death sentence for infected horses. Early treatment improves the chances of a favorable recovery. EHM is more difficult to treat once neurological symptoms manifest. Treatment may involve round-the-clock monitoring, supportive care including the use of anti-inflammatory medications, the use of slings and regular monitoring of bladder status.

The suspected and confirmed cases of EHM/EHV have been primarily from the western region of the United States. However, the full extent of the outbreak is unknown and under investigation, and there is always the risk of contact between horses in the West and other regions if the animals are being transported.

If horse transport is essential, it is particularly important to limit stresses on your horse, as any stresses can make your horse more susceptible to the virus. Make sure to have all your equine health documents organized and your horses loaded in a manner that allows for easy visual examination. This will help facilitate your passage through inspection points. Due to the outbreak, some states are tightening travel restrictions and entry requirements. If you plan to transport your horse across state lines, we recommend you contact the state veterinarian’s office of each state before your departure. To obtain this contact information, check www.aaep.org/us_canada_statehealthoffice.htm.

BLM Action Urged Regarding Threat to Wild Horses

An additional area of concern is the threat to wild horses from this disease. The Humane Society of the United States has requested that the BLM discourage and, if possible and appropriate, prohibit private horse owners from bringing potentially exposed domestic horses onto federal lands where they may contact and possibly infect wild horses or other equines.

Because EHV-1 infection in horses is highly contagious, the possibility of disease transmission from domestic to wild horses is far from hypothetical. For example, if domestic horse owners are permitted to leave hay on the ground that has been picked through by horses carrying the EHV-1 virus, wild horses who frequent campgrounds and other equine recreational areas may move in to eat the contaminated remains of the hay leftovers, and thus, would be exposed to the disease. Since EHV-1 infections can be fatal, should such a scenario occur, the impacts on wild horse populations could be disastrous.

Additional Information and Resources

More helpful information—including FAQs, an archived webinar, state updates and a radio interview about EHV-1 and EHM—is available to horse owners at the American Association of Equine Practitioners (AAEP) website at: http://www.aaep.org/EHV_resourcesowner.htm.

The Center for Equine Health at the UC Davis School of Veterinary Medicine also offers information about the recent outbreak and more information about EHV-1 and EHM in general at: http://www.vetmed.ucdavis.edu/ceh/currenthealth.cfm.

An additional resource is the USDA’s Animal and Plant Health Inspection Service’s Animal Health Monitoring and Surveillance update at: http://www.aphis.usda.gov/vs/nahss/equine/ehv/index.htm.

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