What is Equine Herpesvirus Myeloencephalopathy

board of animal health

Reportable Disease of the Month

Equine Herpesvirus Myeloencephalopathy

What is it?

A disease impacting horses, which develops from an equine herpesvirus (EHV-1) infection. The virus is easily spread between horses and can remain inactive for long periods of time. Horses can be exposed and not suffer serious illness, yet some develop the neurological form of the disease, myeloencephalopathy (EHM). Minnesota horses with a confirmed EHM infection (and those exposed to EHM infected horses) must be quarantined to prevent further spread of the disease. Infected horses are treated with supportive care, because there is no cure for EHM.

In recent years, there has been a marked increase in the number of EHM cases reported across the United States. Outbreaks have been reported at boarding stables, horse shows, veterinary clinics and racetracks; significantly impacting the equine industry. You can visit the Equine Disease Communication Center (EDCC) for a summary of the most recent cases by state: http://www.equinediseasecc.org/alerts/outbreaks?page=1.

How is it transmitted?

Nearly all horses are infected with the EHV-1 by the time they reach two years of age. Foals are generally exposed by contact with their dam. Horses can be life-long carriers of the virus, which can remain inactive, or latent, in the horse’s body. The virus can become reactivated and shed during times of stress including strenuous exercise, transport or weaning.

Active virus can spread from horse to horse through nose-to-nose contact, contact with contaminated objects such as tack, feed and water buckets, grooming equipment, and a person’s hands or clothing. Exposure most commonly occurs via respiratory shedding of the virus.

What are the clinical signs?

The most common clinical signs are fever, incoordination, rear leg weakness, inability to rise, diminished tail tone, and urine dribbling. Contact your veterinarian immediately if your horse is exhibiting any of these signs, or you suspect EHM. Horses may appear to be perfectly healthy, yet continue to spread the virus.

How is it diagnosed?

A veterinarian collects nasal swabs and blood samples from a suspect horse for laboratory testing. Additionally, a dead horse can be necropsied (examined) to confirm EHV-1 disease.

Is there a risk to people?

There is no known EHV risk to people. However, you should always take biosecurity precautions around infected animals to prevent further spread of the disease.

How can it be prevented?

The most important step to prevent the spread of the disease is to isolate affected and exposed horses. Horses should not enter or leave a premises where EHM has been diagnosed until cleared by a regulatory veterinarian. Sick horses, or those with known exposure, should be physically separated from healthy horses. Equipment should not be shared amongst horses. Biosecurity measures such has handwashing and wearing designated clothes and footwear when visiting sick horses should be implemented.

EHV-1 is susceptible to many disinfectants and can be cleaned off of most solid surfaces. The virus is capable of surviving outside of its host in organic material. All manure and feed should be properly disposed of before cleaning and disinfecting underlying surfaces. If equipment must be shared it should be cleaned and disinfected between horses.

Vaccines are available for EHV-1. However, these vaccines are not labeled for prevention of the neurological form of the virus (EHM).

learn more

Having trouble viewing this email? View it as a Web page.