As equine events around the country have been cancelled because of the equine herpesvirus myeloencephalopathy (EHM) outbreak, veterinarians are sharing biosecurity protocols to stop its spread.

Although the number of affected horses in the outbreak is unknown, Dr. Brian Buchanan of Brazos Valley Equine Hospitals in Navasota, Texas, says some cases have been severe.

“Some horses have been euthanized and that is terrible,” he says during a recent Facebook live event. “The disease can be very traumatic. The goal is to avoid exposure. They only way to avoid exposure is [for horses] to stay home.”

What is EHM?

EHM is the neurologic form of EHV-1. Equine herpes virus is a family of viruses that includes EHV-1 through EHV-5. The most common are EHV-1 and -4, according to the Equine Disease Communications Center (EDCC). Usually, cases are limited to respiratory disease and include symptoms such as fever, nasal discharge, lethargy and abortion.

“EHV-1 causes inflammation of the blood vessels and triggers blood coagulation within the brain and spinal cord,” the EDCC says. “Neurologic signs occur as a result of a lack of blood flow and resulting damage to the brain or spinal cord; this disease manifestation is known as equine herpesvirus myeloencephalopathy (EHM). Classic clinical signs of EHM include fever, swelling/stocking up of the limbs, hindlimb weakness, and urine dribbling.”

EHM is spread through nasal discharge from sneezing or snorting or from contaminated surfaces, such as people, clothing, feed, water and stalls. The incubation period is 2-10 days. Some horses can be carriers without any clinical signs, and there is no vaccine to prevent EHM, which is why quarantine is crucial in controlling the spread of the disease, which can have a fatality rate of up to 1 in 4.

“The virus is latent in pretty much every horse,” Buchanan says. “That means the horse gets infected in its first few months of life. The virus incorporates into the horse and some different tissues and hangs out there forever. Just like fever blisters, herpes is forever. When something stresses the horse, the virus becomes active again. The horse becomes contagious, sheds herpes. It spreads to other horses. They become infected and contagious and then it just spreads from there like ripples in a pond.”

Can Farriers Spread the Virus?

While farriers can spread EHM, Buchanan doesn’t believe it’s likely.

“Farriers, by and large, are really good and cognizant of infectious disease and not spreading things around,” he says. “Metal surfaces are easily disinfected. If an owner’s horse is sick and snotty, don’t put the farrier in that position to try to decide what to do. You can wait a week to let that horse recover prior to exposing the farrier to it. It’s been my experience with most farriers is they’re very aware and cognizant of protecting their other clients by using barrier precautions like wearing gloves, washing their hand a lot, which is one of the best things you can do.”

There are other precautions farriers should take during an outbreak.

“Hydrogen peroxide is a product that I like a lot,” Buchanan says. “It has to be diluted correctly and sprayed on. You need appropriate contact time — between 5 and 10 minutes — depending on what you’re trying to disinfect. Most of the phenols are good products and then there’s an ammonia quaternary and a glutaraldehyde mixed product that’s known as a companion. These are disinfectants that don’t destroy the metal and are not toxic to the horse or people.”

Dr. Sammy Pittman, a veterinarian and farrier at Innovative Equine Podiatry and Veterinary Services in Collinsville, Texas, uses a common over the counter remedy that you find in a grocery store.

“Simple, readily available 70% alcohol will kill and disinfect the herpes virus,” he says. “You can wipe your tools down between horses or barns. We’re traveling a lot times between barns more than most people, so the virus can live on our surfaces long enough between barns that you could potentially spread it. Consider changing shirts and hats and just being mindful of nasal secretions and things like that.”

Although people commonly use bleach to disinfect, Buchanan strongly suggests not using it.

“Diluted bleach is a very destructive chemical,” he says. “It’s not a very good disinfectant for our world. It’s not effective against organic debris such as dirt, mud, manure or shavings. If you’re spraying down the trailer with diluted bleach, you’re destroying the metal, but you’re not really disinfecting things if you don’t scrub the trailer first. Metal surfaces, clean surfaces, wood laminate surfaces that aren’t dirty, bleach is fine for that”

EHM has a lifespan of about 2 days on a dry surface, while it increases to 2 weeks on a wet surface under ideal conditions.

If the horses you work on haven’t been off the client’s property for a significant amount of time, the chances of an outbreak at that barn are low. However, Pittman encourages talking with your clients.

“Have an open communication with them,” he says. “Ask if they have been been in and out traveling. If one or more of their horses have been exposed or in quarantine, reschedule them until this quiets down.”

Related Content: EHM Outbreak Disrupts Equine Events, Sparks Biosecurity Concerns