Can Immunomodulators Help Herpesvirus Victims?

Human and animal scientists have been researching ways to stimulate the immune system in order to prevent or mitigate disease, especially just prior to or during stressful events. Options include vaccination, antimicrobial therapy, and immunomodulation (altering the immune system).

Just prior to the annual convention of the 2005 American Association of Equine Practitioners in early December, Pfizer Animal Health held an educational session for veterinarians on equine immunology. Included in the presentations was a report of a study on an immunomodulator used in Europe since the 1990s and which was scheduled to be available in the United States in early February of 2006.

Rob Holland, DVM, PhD, discussed the contact challenge study (done in conjunction with John Donecker, VMD, MS) with the product Zylexis against equine herpesvirus (EHV), which can cause abortion as well as respiratory and neurologic problems.

The respiratory form of EHV-1 and EHV-4 were used to challenge yearlings in two different studies. Half were treated with Zylexis three days and one day prior to exposure to the virus, and again treated two and five days after challenge. Daily temperatures and nasal exudate scores were noted, daily blood samples were obtained for white blood count assays, and nasal swabs were used for virus isolation.

Virus isolation showed that all horses exposed to the virus were positive for herpesvirus starting two days after exposure. Both treated and non-treated horses were infected, had fevers, and had higher white blood cell counts, but treated horses were "less sick," explained Holland. Total nasal exudate scores were significantly lower in Zylexis-treated horses (40% reduction for those challenged with EHV-1 and 61% reduction for those challenged with EHV-4), indicating clinical effect. Treated horses had more pronounced serum neutralization titers than controls at each post-challenge sampling, indicating a greater antibody response to the viral infection by the horse's immune system.

Zylexis-treated horses also had fewer and less-severe secondary bacterial infections.

Holland said giving the immunomodulator two weeks before a stressful event--horse show, sale, traveling, etc.--would be the best management protocol. "This product has been used for eight years in Germany," said Holland. "It won't stop EHV-1 or -4, but it can limit the severity of respiratory symptoms, as shown by total nasal exudate scores."

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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