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Healthy as a Horse

During the equivalent of their preschool years, young horses play, learn, and very often get sick. Like their young human counterparts, these colts and fillies catch all kinds of viruses from their peers.

The worst of these, equine influenza, has terrorized the horse industry, causing animals to get sick and to sometimes further suffer ineffective treatments, and costing millions of dollars in lost racing time. Without the necessary vaccine to control this virus, it has spread practically unchecked.

Until now.

Thomas Chambers and Robert Holland in the UK College of Agriculture's Department of Veterinary Science, with laboratory help from Lynn Tudor, have pinned down the wild virus types responsible for equine influenza. They have also helped to conduct some of the rigorous trials for the vaccine, which was developed in tandem with UK by University of Pittsburgh virologists.

Thanks to the efforts of this group, the horse industry in the United States now has the first equine influenza vaccine of its type: Flu Avert I.N.—a knockout punch to the virus. The vaccine is licensed by the USDA and distributed by the Heska Corporation.

Like kindergarten kids, practically all young horses are exposed to influenza at some time, according to Chambers. They are most vulnerable when they are about eight to nine months old, when the antibodies they get from their mother's milk wear off. At this age they might be sold or put into race training, and the stress of these experiences only makes them more susceptible. They suffer many of the same symptoms that humans do.

"They'll get a fever, they'll get snotty noses," Chambers says. "They'll be depressed, lose weight and muscle tone. They can develop the horse equivalent of shin splints from a loss of bone density. Maybe half the time they will get a secondary infection."

In fact, it is these secondary infections that prove the most serious. The flu damages the protective lining of the horse's nasal passage and upper respiratory tract, allowing other germs to settle deep into the lungs. These secondary infections are usually more severe than the first one, says Chambers, and can be life-threatening.

It takes the horse a minimum of three weeks to recover, but the process can take up to three months. Returning to racing too early may only lengthen an animal's recuperation time.

This new vaccine blankets the horse with a rate of 93 percent effectiveness. "Nothing's 100 percent, but this comes close. Even the people at the USDA were impressed," Holland says.

In five to 10 seconds a vet can administer the vaccine through a nasal applicator to create the appropriate antibody reaction in the horse's protective nasal linings. This application triggers an immune response right at the site where influenza strikes. It's not a miracle drug, however—it takes a couple weeks before the horse is fully immune, just like vaccines for humans.

One of the things Chambers and Holland are most proud of is that all the team's hard work is rooted in firm scientific proof of the vaccine's effectiveness.

"That's becoming more and more apparent to the USDA—not just safety but full-scale efficacy," Holland says. "Instead of having vaccines that might work, we have a vaccine that does work."

Jonathan Riggs