Looking Back: 2011 EHV-1 Outbreak

"It won't happen to my horse." "I haven't taken my horse anywhere; he'll be fine." "That disease hasn't been in our area." Think your horse is immune to the threat of infectious equine diseases because of a protected lifestyle? You might want to think again.

In late April 2011, horses attending an equine event in Ogden, Utah, were exposed to equine herpsevirus-1 (EHV-1). Just three months later, when the USDA Animal Plant and Health Inspection Service (APHIS) declared the outbreak contained, more than 2,000 horses had been exposed. Of those, 90 tested positive for the virus or its neurologic form, equine herpesvirus myeloencephalopathy (EHM). Ultimately, 13 horses died or were euthanized as a result of the disease.

Just over half of the 90 horses actually participated in the Ogden event, demonstrating the highly contagious nature of EHV-1 and its ability to spread quickly. The remaining 36 horses contracted the virus due to secondary or tertiary exposure. Cases were confirmed in 10 states, stretching from Oklahoma to California.

In January 2012, 17 cases of EHV-1 were confirmed in California. "EHV-1 is so easily spread that it can affect a number of horses before owners even realize there is a problem and are able to take containment measures," said April Knudson, DVM, equine specialist for Merial Veterinary Services. "The disease can spread from horse-to-horse contact, but also by horses touching objects contaminated with the virus, including clothing, human hands, equipment, rags, feed/water buckets and tack," she added.

Although it's not transmissible to humans, EHV-1 is highly contagious among horses and camelids, and it is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions. The disease can cause a variety of ailments in equines, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (EHM, the neurologic form).

Myeloencephalopathy is characterized by fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. Should a horse with potential EHV-1 exposure display any of the aforementioned clinical signs, a veterinarian should be called to obtain samples and test for the disease.

Equine influenza is another highly contagious disease. It can compromise a horse's respiratory tract and spread quickly through a herd. Clinical signs can include high fever, nasal discharge, dry cough, depression, anorexia and weakness.

"To guard against ... communicable diseases such as these and others that spread by insects or even other animals, the most important things horse owners can do are vaccinate and be aware of disease threats," said Knudson. "With competition season getting underway, many people will be traveling, possibly into areas where the risk of equine disease has been identified. Merial's Outbreak Alert program is a great way to help horse owners and veterinary practices stay informed."

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