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As EHV-1 Outbreak Continues, Veterinarian Suggests Owners Implement Preventive Measures

Equine Resources International, LLC

In Kentucky, two equine facilities located more than two hundred miles apart have now experienced equine herpesvirus type 1 (EHV-1) outbreaks. A number of horses stabled at Turfway Park in Florence, KY and two horses from the Western Kentucky Training Center, located south of Henderson, KY, have tested positive for the virus. Additionally, eight horses stabled at Pimlico Race Course in Baltimore, MD have either tested positive or are suspected of EHV-1 infection.

Testing indicates that the virus has circulated in Barn 26, Barn 27 and the Outrider and Pony Barns at Turfway Park, beginning December 21 with one reported case in Barn 26. Barns 26 and 27 have been placed under quarantine, and the horses housed in the Outrider and Pony Barns have been moved to a quarantine facility off the grounds. A number of horses from all three barns have either tested positive or showed symptoms of the disease, and two horses have been euthanized due to neurological disease attributed to EHV-1. On Sunday, January 8, two horses at the Western Kentucky Training Center presented with symptoms of stiffness and fever, and later tested positive for EHV-1. That facility is also under quarantine.

Pimlico’s outbreak began on January 2, when one horse stabled in Barn 5 was euthanized due to neurological symptoms. On January 13, an additional case from Barn 6 resulted in euthanasia. Barns 5 and 6 are currently under quarantine.

“Other than supportive therapies to reduce symptoms such as fever, there is no effective treatment once a horse has been infected with EHV-1,” said Rob Holland, DVM, Senior Veterinarian at Pfizer Animal Health. “Owners may be able to reduce the risk of transmitting EHV-1 between horses by limiting or thoroughly disinfecting shared equipment, such as water buckets, bits and lip chains.”

EHV-1 commonly causes respiratory disease, but the virus can also affect the central nervous system, resulting in various levels of paralysis. Horses with mild signs usually have a good chance of recovery, but horses that become unable to stand have a poor rate of survival. Horses may become infected without ever showing clinical signs, and act as carriers for the disease. Also, the herpes virus has the ability to become latent and hide from the immune system, and an infected horse may periodically shed the virus throughout its lifetime.

“I would recommend that healthy horses about to be shipped or exposed to unknown horses get vaccinated with Rhinomune® according to label indications,” said Dr. Holland. “This vaccine contains a modified live EHV-1 virus that triggers a very effective immune response.”

In a limited study by Klaus Osterrieder, DVM, associate professor of virology in the College of Veterinary Medicine at Cornell University in NY, horses were vaccinated against EHV-1 and then exposed to a strain of the virus retrieved from a 2003 outbreak at the University of Findlay in OH in which more than 90% of 138 infected horses displayed neurological symptoms. According to the results of the study, presented at the annual American College of Veterinary Internal Medicine Forum in June 2005, horses vaccinated against EHV-1 using the modified live vaccine (MLV) Rhinomune in a two dose booster series had consistently lower fevers, no neurological disorders and less virus in nasal fluids compared to those vaccinated with an inactivated vaccine, which employs a killed virus to activate an immune response.

Rhinomune is approved for use as an aid in preventing respiratory disease caused by EHV-1 and can be given to healthy horses three months of age or older. It is safe for pregnant mares past 60 days of gestation and has a low incidence of injection site reactions such as swelling and stiffness. Vaccination of all horses kept at a specific location is recommended to enhance herd immunity. After the initial series of two doses given three to four weeks apart, revaccination with a single does is recommended every three months depending on the risk of exposure. Owners should discuss vaccination and booster schedules with their veterinarian to determine a program that best suits each horse.

For more information on Pfizer Animal Health’s complete line of equine health care products, visit Pfizer Inc discovers, develops, manufactures and markets leading prescription medicines, for humans and animals, and many of the world’s best known consumer products.