West Nile Virus Treatment Licensed

Novartis Animal Vaccines announced Aug. 19 the conditional licensing and availability of the only antibody product approved by the USDA to help control disease caused by West Nile virus (WNV) in equids. This product helps an exposed animal by increasing the antibody level in the circulatory system, which enhances an animal’s ability to neutralize virus already in the blood. The approval was announced on Aug. 7 to USDA officials and state veterinarians.

For a product to receive conditional approval, the company must show that the product is safe, pure, and that there's reasonable expectation of efficacy.

West Nile Virus Antibody is a prescription antiserum product that is administered intravenously by a licensed veterinarian. The product is diluted into lactated ringer’s solution to obtain a total administration volume of one liter. The solution must be warmed to body temperature prior to administration, and it is slowly administered using a sterile technique.

Amy Glaser, DVM, PhD, a senior research associate in the animal health diagnostic laboratory at the Cornell University College of Veterinary Medicine, where the product was shown in studies to neutralize virus in horses’ blood, explained, “An antiserum is a passive immunization scheme, which introduces only proteins which interact with a specific antigen, but there is no active immunity induced after their administration. They’re most useful for trying to reduce an antigen load in an animal which is currently experiencing an infectious disease.”

Richard Harland, DVM, director of research and development for Novartis Animal Vaccines, said, "When it comes to caring for horses that have the West Nile virus, veterinarians' options have been limited. Novartis has responded to this urgent need by developing a product that works against the virus."

Product Use

Elizabeth Davis, DVM, Dipl. ACVIM, assistant professor in equine internal medicine at Kansas State University’s College of Veterinary Medicine, will be using the product in select cases of WNV admitted to the veterinary hospital.

Davis said, “Where I think it’s going to be applicable is in a patient that doesn’t have its own circulating antibodies against the virus (unvaccinated or previously unexposed) and we can rapidly administer and help bind some of those virus particles.” But she emphasizes the importance of treating the horses early in the course of disease--within the first three days of observing clinical signs (typically neurologic deficits, including ataxia, depression, weakness of limbs, partial paralysis, or muscle twitching).

She added that the treatment should not be cost-prohibitive.

Safety Studies

“Field studies involving 106 horses demonstrated the product is safe when administered according to label directions,” said Harland in a company Q&A on the product. He suggested premedicating the horses with flunixin meglumine (Banamine) to reduce the risk of anaphylactic reactions (rapidly developing, exaggerated, sometimes life-threatening allergic reactions), which are not likely but might occur. If anaphylaxis occurs, symptoms should be treated with epinephrine.

“It appears to be a safe treatment,” said Davis. “The label says to use one time and one time only, so you don’t have to worry so much about anaphylaxis, which you might have a problem with on repeat administration. It’s a small volume, easy for a practitioner to use, and one of the few specific forms of therapy available that can potentially benefit WNV-affected horses.”

Expectations of Efficacy

According to Novartis, a Cornell University study demonstrated the ability of the product to neutralize WNV. "Based on the study, researchers concluded there is a reasonable expectation of efficacy when the West Nile Virus Antibody is administered to horses that have been exposed to the virus," a release from the company stated.

More studies are underway to prove the efficacy, but one study has shown that adult horses given the product developed a high antibody titer of 1:70. The titer reflects directly on the ability of the antiserum to neutralize virus, explained Harland. The higher the titer, the more individual viral particles that can be neutralized and the better the possibilities of stopping infection and replication of the virus in the horse.

According to Schulz-Thomas, the company hopes that they can obtain a full license for the product during 2004 by completing and turning in the results of efficacy studies. A USDA conditional license expires in a year, and if those required efficacy studies aren’t complete, the company must show good research progress in order to have the conditional license renewed.

When a product has a conditional license, each state must approve its use. Schulz-Thomas said the company has received many letters from state veterinarians wanting to make the product available to practitioners in their state.


Schulz-Thomas said that when WNV is detected in a herd, there are obviously disease-carrying mosquitoes in the area, and other horses are in imminent danger especially if they are unvaccinated. (Horses do not have significant enough viremia, or virus in the bloodstream, to spread the virus among themselves, but stablemates will be exposed to the same infected mosquitoes).

In a situation like this, the product can be administered preventively. “The vet has a lot of discretion on how he or she wants to treat an individual animal. Even if the animal has been vaccinated, there have been some vaccine failures. Obviously a herd that has not been vaccinated (contains viable candidates for treatment). Some people will want to do anything they can, but in my opinion, it’s probably going to get used more on non-vaccinated animals in areas where other animals have developed disease.

“I don’t see any contraindications for using it in a vaccinated animal either,” she added.

Schulz-Thomas notes that it might be a good idea to begin treating a suspect WNV case with the product before test results are returned. While the problem might be another disease, administration won’t hurt the animal, and the earlier treatment will be helpful if the cause is WNV, she explained.

After administration, Davis said, “We would want to see them at least stabilized within 12-24 hours of receiving the treatment.” Schulz-Thomas gave a similar response, extrapolating from research in humans treated with WNV antibody plasma--if the patients responded favorably, they did so within 24 hours.

What is extremely important to remember is prevention: Reducing the sources of mosquitoes that carry the virus--thereby decreasing the chances of exposure--and vaccinating horses at risk.

“We don’t want people to go into it thinking no matter how sick, or how close to death the horse is, that you’re going to give the product and have a miraculous recovery. You must have a realistic expectation,” she said.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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