EHV-1 Neurologic Disease a Challenge for Researchers

Despite the remarkable advances in understanding neurologic disease in horses, including the identification of the single genetic mutation that gives rise to the neuropathogenic form of equine herpesvirus type-1 (EHV-1), virologists continue to experience frustrations when it comes to studying EHV-1 in the experimental setting.

EHV-1 causes abortion, neonatal death, and myeloencephalopathy in horses. It is known that EHV-1 can lie dormant in lymph nodes, lymphocytes (a type of white blood cell), or the trigeminal nerve, and can be reactivated at a future point in time to potentially infect susceptible horses.

It is also known that not all horses are equally susceptible to EHV-1 infection. Horses younger than three years of age have a lower risk of developing neurologic disease whereas Warmblood breeds, Thoroughbreds, and Standardbreds are more commonly affected than other breeds such as Shetland and Icelandic ponies.

In an attempt to create a model to better study the secrets of the neuropathogenic strain of EHV-1, Marianne M. Sloet van Oldruitenborgh-Oosterbaan, DVM, PhD, Dipl. ACVIM, and colleagues attempted to infect four horses with the neuropathologic form of EHV-1 using a large, inhaled dose inoculation. Only one of the four (25%) horses developed characteristic signs of EHV-1-associated myeloencephalopathy (EHM) which was accompanied by viremia (EHV-1 in the bloodstream).

But all was not lost. The research team did conclude that horses with a low frequency of the pre-cursor antigen-specific cytotoxic T lymphocytes (a type of infection-fighting white blood cell) might be more likely to become viremic and should be selected for in future studies.

Van Oldruitenborgh-Oosterbaan's research team is also looking at changes in cerebral spinal fluid composition in viremic horses to determine if these changes can predict which horses will develop EHM.

The study, "Experimental infection with neuropathogenic equid herpesvirus type-1 (EHV-1) in adult horses," is scheduled to be published in an upcoming edition of The Veterinary Journal. The abstract is available on PubMed.  

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.