It was a disaster for Maryland horsemen. An outbreak of equine herpesvirus, also known as EHV-1, ran rampant in December and January through flat track training barns at Pimlico, Laurel, Bowie and eventually Fair Hill. Horses were quarantined, and racing and training losses cost horsemen precious dollars, as the repercussions affected racing and other sports up and down the East Coast.

The neurological strain of the virus resulted in the deaths of several race horses, and even spread outside the racing circle when eventer Kim Meier-Morani, of Worton, Md., was hard hit after an infected race horse arrived at her barn, infecting her sport horses, two of which had to be humanely destroyed.

On Feb. 21, more than 200 people, including track officials, veterinarians, state officials and horse owners, gathered at Fair Hill, Md., to hear the latest updates on the outbreak and to analyze the situation.

The Facts

Dr. Robert Holland, from Pfizer Pharmaceuticals, said EHV-1 is one of the two rhinoviruses that can cause respiratory infection in horses. EHV-4 can also cause respiratory infection, but it has not been shown to affect other systems.

EHV-1 can cause respiratory signs, neurological signs, abortion or an apparent infection. Respiratory signs can include a high fever (102-104 degrees), which can spike and return to normal within 12 hours and/or be intermittent.

Neurological signs can range from ataxia (lack of coordination) to complete paralysis and can progress rapidly or can remain fairly static. Abortion is another manifestation of EHV-1 infection.

Inapparent infection can also occur, where the horse shows no signs at all. More than 80 percent of horses over the age of 1 have been exposed to EHV-1 and latent infection can also take place. It’s not clear how long the virus can be latent, however.

When EHV-1 results in neurological symptoms, they’re caused by damage to the blood vessels in the spinal cord and brain. Many veterinarians equate this damage to “mini-strokes.” Horses that develop the neurological form of EHV-1 are a small percentage of those infected, but they may show signs that rapidly progress to paralysis and death or euthanasia.

The disease and the neurological manifestations are not new; these symptoms were described as early as the late 1800s. Today’s technology, with the development of more sensitive tests, now allows earlier and faster diagnosis of the virus.

It does seem that more neurological cases are occurring in clusters, however, unlike a few years ago, when mostly single cases were seen, noted Holland.

Nasal swabs and blood samples test for EHV-1. Nasal swabs indicate the virus in nasal secretions, which is how the virus is transmitted. Serum samples may indicate current or resolving infection.

The virus is most likely spread through direct contact with nasal and oral secretions. The virus lives for one to three days in secretions and may live up to seven days in water. The full course of the disease is usually eight to 10 days, with an incubation period of 10 to 14 days.

The best prevention is through hygiene measures. Do not share equipment, water buckets or feed tubs between horses. Hand-to-nose contact, bits, stud chains and towels can also spread disease.

Those handling horses should clean their hands thoroughly with alcohol-based hand sanitizers in between horses. It’s not even a bad idea to change clothes if you can.

Scrub all equipment (not just spray) between horses. Restrict outside contact, especially physical touching, between horses. Use phenolic-based disinfectants in trailers and stalls. (This includes Techtrol and One Stroke).

New arrivals should be isolated from the other horses. Isolation and checking the horse’s temperature twice daily may catch early cases and prevent spreading. Don’t allow new horses to commingle with farm horses or have contact over a fence line.

Fair Hill Is Proactive

Dr. Kathy Andersen, of the Fair Hill Training Center, gave a detailed day-by-day synopsis of the Fair Hill Training Center’s response to the virus.

At the first sign of a fever, horses were tested for EHV-1, and all horses in that same barn were treated as suspects. The barn was immediately placed in strict isolation–quarantine was enforced and no visitors were allowed in the affected barn.

The horses in that barn were not allowed on the track at the same time as horses from other barns, and no shared equipment (starting gates, for example) was used with quarantined horses.

Horses were travel-restricted from the entire training center. At this time, only horses in a single barn had fevers. When the first horse with a fever tested positive for EHV-1, then all horses in that barn were tested. Ten horses had positive results and fevers, and they were all confined to a single barn on the property.

Andersen stressed that the quarantine and isolation procedures were strictly voluntary and that the state had had no input in Fair Hill’s decision. Because no horses had developed the neurological form of EHV-1, the state had no requirements for isolation or testing and never put hold orders or other restrictions in place.

Andersen invited Dr. Rusty Ford from Kentucky to the Fair Hill Training Center to evaluate their response to the disease threat. He complimented Fair Hill on their proactive approach and their thoroughness. He also discussed his experiences with the disease and management at the recent outbreak at Turfway Park in Kentucky.

“EHV-1 is always a threat to the equine population,” he said. “And proper management will reduce losses from this disease, but never eliminate all risks.”

Dr. Guy Hohenhaus, the Maryland state veterinarian, discussed and defended the Maryland Department of Agriculture’s approach to the outbreaks. He said that Maryland officials had handled the outbreak well and that he was happy with how the disease had been contained. Three separate facilities were affected by this one outbreak.

After Hohenhaus spoke, he answered questions, several of which centered on Maryland’s protocol and response to the neurological form of EHV-1.

Hohenhaus indicated that all equine neurological disease would now be reportable in Maryland, although he did not say this was a direct result of this outbreak.

Several questions addressed whether Maryland should take a more proactive approach to disease prevention, such as implemented by Kentucky. Kentucky requires health certificates for horses leaving or entering tracks affected by the disease, as well as mandatory vaccination. Hohenhaus stated that he did not think this necessary yet.

No Vaccine Prevents Neurological EHV-1

Dr. Rob Holland, of Pfizer Pharmaceuticals, stressed that at this time there’s no vaccine that provides protection against the neurological form of EHV-1.

Dr. Pam Wilkens, of New Bolton Center at the University of Pennsylvania, cited a recent, unpublished study that suggests that cell-mediated immunity may be more protective than humoral immunity and that future vaccine strategies might include those vaccines.

Frequent (90-day) protocols (vaccination schedules) and herd immunity are important in protection against the spread of the respiratory disease. It’s also important to isolate showing or racing animals from the general population.

Holland recommended that horsemen consult with their veterinarians to set up a vaccination program tailored to the needs of their horses.