The typical veterinarian's arsenal against equine herpesvirus includes vaccination to prevent the disease and supportive care/antiviral medication when the disease strikes. However, one more weapon might eventually be added to that list, somewhere in between vaccination and treatment: siRNA administration during outbreak conditions.

Small interfering RNA, or siRNA for short, is a Nobel Prize-winning technology that Cornell University researchers have been studying for equine use. At the 2009 American Association of Equine Practitioners Convention, held Dec. 5-9 in Las Vegas, Nev., a study on the efficacy of siRNA treatment against equine herpesvirus-1 (EHV-1) infection was presented by Margaret M. Brosnahan, DVM, MS, Dipl. ACVIM, a post-DVM graduate student at Cornell.

"Complete prevention of EHV-1 infection is ideal, but unrealistic," she commented, noting that the virus can become dormant in the body (latent infection) and reactivate later. Also, immunity from vaccination is very short-lived, making it very hard to completely prevent disease. "So our goals are to reduce viral shedding, minimize disease transmission, reduce viremia (levels of virus in the bloodstream), and reduce the severity of clinical signs."

The treatment strategy used siRNAs targeted against two different EHV-1 genes involved in viral entry and replication. Equine herpesvirus can replicate (reproduce) very quickly, generating large amounts of virus to sicken the horse and spread to others. Thus, inhibiting its replication would logically reduce viral shedding into the environment (and thereby disease transmission), viremia, and the severity of clinical signs of disease