EHV-1 Testing

AQHA Professional Horseman Al Dunning weighs in on his experience with EHV-1 testing, and Dr. Tom Lenz suggests alternatives to testing.

The American Quarter Horse Journal

AQHA Professional Horseman Al Dunning's three horses who contracted equine herpesvirus-1 myeloencephalopathy while at the National Cutting Horse Association Western National Championships April 29 - May 8 in Ogden, Utah, are on the road to recovery. However, in the 24 hours since we talked to Al, he has had several other horses that now have elevated temperatures and one horse that has tested positive for EHV-1 through a nasal swab test. 

“He was in Ogden. He’s healthy, he’s happy, he’s eating, he isn’t wobbling, he has no temperature, but he came back positive with the nasal virus,” Al says of the only horse that tested positive out of his 10 horses who were tested for EHV-1. “We’re doctoring him. We’ve got a couple other temperatures that might be elevated, but we’re treating them just like they’re the virus. We’ve got seven that we’re treating, but only four of them are confirmed cases.”

Al was surprised to find that the horse who tested positive for nasal shedding of EHV-1, which is how the virus is spread, didn’t have a positive blood test. But just because the test results are negative for the disease doesn’t mean that Al isn’t taking as many precautions as possible.

“Normally, people don’t take temperatures twice a day, every day,” Al says. “We’re having some temperatures on some of the stay-at-homers. But we’ve had rain one day, we had cold, we had hot, now it’s kind of medium.”

Dr. Tom Lenz, past president of the American Association of Equine Practitioners and a regular columnist in The American Quarter Horse Journal, says that there are measures that horse owners can take to protect their horse from EHV-1, even if the horse has been exposed to the virus.

“If I had an exposed horse,” says Dr. Lenz, “I’d put it on a course of Zylexis, an immune modulator, that stimulates interferon production and bolsters the immune system. I’d also consider giving them a booster vaccine injection of a high antigenic mass vaccine (those used to prevent EHV abortion) like Pneumabort-K, as it has been shown to decrease viremia.”

Viremia is virus in the bloodstream. Horses who develop the neurological form of EHV-1 experience two very high viremia spikes prior to coming down with neurological symptoms.

Dr. Lenz also says that it’s important to keep in mind that there are different forms of EHV-1.

“EHV-1 can cause upper respiratory infection, abortion and a neurological form of the disease,” says Dr. Lenz. “Very, very rarely do infected horses develop the neurological form of the disease. Usually, they are very old horses, young horses or stressed horses that have an impaired immune system. Horses traveling long distances to shows and then stressed at the show fall into that class.”

If a horse owner wants to test his or her horse for EHV-1, Dr. Lenz says that in addition to looking for viremia spikes in blood work, there are a few other testing options. 

“The PCR (polymerase chain reaction) test is the gold standard for diagnosing the condition,” says Dr. Lenz. “The PCR test looks for the EHV’s DNA. When you get a positive, it indicates that the horse has been infected by EHV but doesn’t indicate if it will develop the neurological form of the disease.

 “A low white blood cell count does indicate that the animal may be dealing with a viral infection, but it is not specific for EHV or any other virus,” he says. “You can run an antibody titer test, but blood titers for EHV don’t mean much, as some horses with the disease have low titers, while others that are latently infected may have relatively high titers.” 

Al says that it took three days to get the results of his horses’ blood tests and nasal swabs, which were sent to the University of California-Davis, which assured Al that its lab technicians were working day and night to process tests.

In the meantime, Al has administered Valtrex to the horses on his place with elevated temperatures and is giving all of his horses rest to bolster their immune systems.

“The vet said, ‘Lock the gate, no horses out.’ We can’t have any stress on them. We just cut back on the feed a little bit so they don’t get fat,” Al says. “We’re hoping this blows over here in the next week or so.”