Equine Respiratory Diseases

Influenza, equine herpesvirus, and strangles were the diseases highlighted by Bonnie Rush, DVM, MS, Dipl. ACVIM, professor and section head of equine internal medicine at Kansas State University, at a seminar on infectious respiratory diseases sponsored by Fort Dodge Animal Health in Lexington, Ky., on Feb. 4. Rush emphasized the importance of vaccinating against these diseases.

"Influenza vaccines are more effective today than a decade ago," began Rush. "Strains of influenza in the vaccine are more relevant to the current strains of influenza in North America, and the vaccine adjuvants (additives that enhance immune response) are more effective."

Challenge studies indicate that killed influenza vaccines offer protection against viral shedding, fever, weight loss, and nasal discharge, said Rush. Performance horses should be vaccinated every three to six months against the disease, while foals should begin a series of three influenza vaccines at nine months of age. If you are giving your horse a modified live influenza vaccine, it should be administered every six months.

Equine herpesviruses type-1 and -4 (EHV-1 and EHV-4, also known as rhinopneumonitis or equine herpesvirus) were discussed as the diseases capable of being carried by an individual horse for a period of time without showing clinical signs, with the virus being shed when the horse was stressed. The neurological strains occur sporadically and can devastate horse populations. "Several years go by where we don't see a case, then a disastrous outbreak occurs, such as at Findlay," noted Rush, referring to an EHV-1 outbreak that killed 12 horses at the University of Findlay in February 2003. She said competition horses and those traveling a lot should get EHV vaccinations every three months. Rush believes that foals should begin a series of three vaccinations for EHV when they are three to four months old.

Strangles was the final respiratory disease discussed; both intramuscular and intranasal strangles vaccines are available. Horses that have had strangles in the past year or have been recently exposed to strangles should not be vaccinated.

Rush also spoke of a common situation for horse owners when a boarding stable requires horses to be vaccinated against strangles. "If you are going to board at a barn that requires all horses to be vaccinated against strangles, check your horse's titer (amount of antibodies in the blood) first. The vaccine is contraindicated if your horse's titer is greater than 1,600," said Rush. If your horse has a high titer, then vaccinating your horse against strangles would not offer him any more immunity than he already has, and might result in purpura hemorrhagica (a condition associated with overzealous immune response to strangles that is characterized by extensive collections of fluid and blood in tissues beneath the skin, primarily on the head and legs). You should receive a waiver from your veterinarian saying there is no need to vaccinate your horse against strangles if the titer is already high.

Above all, Rush reiterated the importance of preventing infectious respiratory diseases in horses by vaccinating them on a regular basis according to the AAEP Vaccination Guidelines (which can be found at www.xcodesign.com/aaep/displayArticles.cfm?ID=171.

About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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