New EHV-1 Testing Protocol Indicates Infectious Risk

Not only can DNA-based tests indicate whether or not a horse is infected with equine herpesvirus-1 (EHV-1), these tests can also measure the amount of virus in the horse's nasal secretions.

"Virus isolation has been the gold standard test for EHV-1, but have recently been replaced by polymerase chain reaction (PCR) tests," reported Nicola Pusterla, DVM, PhD, Dipl. ACVIM, associate professor in the Department of Medicine and Epidemiology at the University of California, Davis, School of Veterinary Medicine "The problem is, routine PCR assays for EHV-1 are unable to differentiate between replicating and non-replicating virus, making interpretation of a positive result challenging for equine practitioners."

Pusterla and his California research team collected nasal secretions from both naturally and experimentally infected horses and used four different calculation methods to quantify EHV-1 viral loads in the nasal swabs.

"Being able to quantitatively report results for EHV-1 viral loads rather than simply reporting whether a horse is or is not infected constitutes an important advance in both the research and diagnostic fields," advised Pusterla.

Specifically, a quantitative test for EHV-1 will allow veterinarians to determine the infectious risk of affected horses, disease stage (i.e., lytic or non-replicating), and response to antiviral therapy.

Pusterla noted the Lucy Whittier Molecular Diagnostic Core Facility at Davis offers complete PCR analysis, including quantitative results, detection of neurotropic and non-neurotropic strains, and, if needed, the detection of transcripts for the late genes as a definitive confirmation of lytic versus non-replicative infection.

The study, "Comparison of four methods to quantify Equid herpesvirus 1 load by real-time polymerase chain reaction in nasal secretions of experimentally and naturally infected horses," was published in the November 2009 edition of the Journal of Veterinary Diagnostic Investigation. The abstract is available on PubMed.

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