Veterinarian: Take Precautions to Protect Horses from EHM

Veterinarian: Take Precautions to Protect Horses from EHM

Contact your veterinarian if your horse's temperature is 101.5°F or higher; a normal, healthy temperature for a horse is around 100°F, and a fever is often the first sign of EHM.

Photo: Stephanie L. Church, Editor-in-Chief

It's springtime and for many horse enthusiasts, that means heading out to horse shows and rodeos. But recent cases of equine herpesvirus myeloencephalopathy (EHM) after a barrel racing event in Nebraska should serve as a reminder that good biosecurity practices can help prevent illnesses, says a Kansas State University (K-State) veterinarian.

Elizabeth Davis, DVM, PhD, Dipl. ACVIM, a professor of clinical sciences in K-State's College of Veterinary Medicine referred to two cases of EHM that were diagnosed after a large barrel racing event that took place in Lincoln, Nebraska, on April 10-13. One of the horses, from a farm in northeast Kansas, became ill after its return from the competition, the Kansas Department of Agriculture said. The horse was euthanized and samples tested by the Kansas State Veterinary Diagnostic Laboratory and Equine Diagnostics Services in Lexington, Kentucky, confirmed EHM. Another confirmed case was a horse from Wisconsin that also was present at the Nebraska event.

"EHM can be highly contagious," said Davis of the neurologic disease associated with equine herpesvirus (EHV-1) infections. "If we're not careful, this virus can spread and can be life-threatening."

The virus that causes EHM is EHV-1, which is common and can be present in a horse for years, causing a minor illness when first contracted. Most cases never develop into EHM. Most commonly EHV-1 causes mild to moderate respiratory disease, abortion in pregnant broodmares, and illness in young foals. Only rarely EHV-1 actually causes EHM. In some cases and especially in times of stress, however, the virus can be reactivated and shed to other horses. Stressful situations such as strenuous exercise, long-distance transport, or weaning can be the trigger for viral shedding.

"What determines whether a horse gets sick is its immune system," Davis said. "If a horse's immune system is not strong and the animal is under stress, EHV-1 can develop into EHM. We usually see this after horses have been in a large group, such as at horse shows, rodeos or race tracks."

Clinical sighs usually start with a fever. The illness can progress, and the horse can show signs of weakness and a lack of coordination. Urine dribbling and lethargy could also signal the disease, and sometimes the illness progresses to a horse going down, Davis said. In the worst cases where the animal can't rise, also called recumbency, they can die or are so ill that they will be euthanized.

Davis provided several tips and facts horse owners should remember:

  • EHM is easily spread by direct horse-to-horse contact. It can also be spread by contact with contaminated objects such as tack, grooming equipment, feed and water buckets, and people's hands and clothing.
  • Contact your veterinarian if your horse's temperature is 101.5°F or higher; a normal, healthy temperature for a horse is around 100°F.
  • There are vaccines available to boost a horse's immunity. They're labeled to fight respiratory disease and abortion, but they're not labeled for the prevention of EHM. Work with your veterinarian to select an ideal vaccine program for your horse.
  • Some horses recover from EHM, but not without treatment. In some cases, even treated horses can die.
  • People cannot get sick from EHV-1 so there is no threat to humans. It is most commonly an equine disease, although it can occur in camelids, such as llamas and alpacas.

Davis said she is not recommending that horse owners stay home from competitions, based on the recent cases.

"Personally, I think if we were going to have a major outbreak, we probably would have seen more cases by now," she said. "We're more than two weeks out from that and no other cases have been reported at this point."

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