Researchers Work to Better Diagnose, Treat Neurologic Herpesvirus

In their efforts to understand how equine herpesvirus-1 myeloencephalopathy (EHM) works, researchers are discovering better ways to diagnose, treat, and prevent the spread of the disease. In a review paper published in The Veterinary Journal, researchers with the University of California, Davis, summarized new developments and their implications.

A recent development is the polymerase chain reaction (PCR) test, which is used to detect virus DNA in a sample. The PCR test uses the same process that nature uses to replicate DNA. In the polymerase chain reaction, DNA products are duplicated many times so they can be detected, and processed through a gel medium to indicate if the virus' DNA is present. While a conventional PCR test indicates the presence of viral DNA, it is time-consuming to set up and might provide false-positive results.

"There is a temptation to interpret PCR in a qualitative way," said study coauthor Nicola Pusterla, DVM, PhD, Dipl. ACVIM. "Positive means infection; negative means healthy. It is more complex than that."

Because healthy horses may carry latent virus, the quantity of the virus in the system is important. Real-time PCR uses an additional molecule, called a probe, to collect and count the test molecules as they replicate. The probe method is more sensitive, and can be performed more quickly than conventional PCR.

Armed with better knowledge about the virus, and a faster and more sensitive test, researchers can develop improved treatments.

Since damage to blood vessels accompanies EHM, it is possible that non-steroidal anti-inflammatory drugs (NSAIDS) and corticosteroids can help prevent blood vessel damage that accompanies the early stages of the disease. Additionally, two antiviral drugs, acyclovir and valacyclovir, can decrease the viral load in individual horses.

Several new treatment technologies are on the horizon including vaccine vectors (using harmless viruses or bacteria to deliver vaccine) and gene therapy (introducing genes that interfere with the virus disease process), as well as introducing weakened viruses that provide immunity. The ideal vaccine would interfere with the virus mechanisms that infect white blood cells initially, as well as viral DNA replication that occurs in cells after infection.

The key to preventing this disease is awareness.

"Just as you protect yourself during the flu season, use common sense and awareness about your horse," said Pusterla. "Keep up a regular vaccination schedule and try to minimize stress when traveling or attending shows."

Take your horse's temperature on a regular basis at shows and events, or when he has been exposed to a new equine population.

"If he does have a fever, don't ignore it," Pusterla said.

Horses with confirmed cases must be isolated to prevent them from contaminating the barn and contributing to the spread of disease.

The American College of Veterinary Internal Medicine (ACVIM) will publish its consensus statement on EHM this month. The statement will provide the veterinary community with the most up-to-date information the diagnosis and treatment of EHM.

Authors of the study, "Equine herpesvirus-1 myeloencephalopathy: a review of recent developments," included Pusterla, W. David Wilson, BVMS, MS, MRCVS; John E. Madigan, DVM; and Gregory L. Ferraro, DVM.

Read more about equine herpesvirus.

About the Author

Nancy Zacks, MS

Nancy Zacks holds an M.S. in Science Journalism from the Boston University College of Communication. She grew up in suburban Philadelphia where she learned to ride over fields and fences in nearby Malvern, Pa. When not writing, she enjoys riding at an eventing barn, drawing and painting horses, volunteering at a therapeutic riding program, and walking with Lilly, her black Labrador Retriever.

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