Few horse health conditions have garnered as much attention across the country in recent years as equine herpesvirus-1 (EHV-1). And for good reason. When it comes to a virus that can hide dormant in a horse for decades or kill him in a matter of weeks, owners can’t seem to get enough information.

While veterinarians have a good grasp on many aspects of EHV-1, researchers are always working to better understand this ubiquitous ailment. Case in point: Nicola Pusterla, DVM, PhD, Dipl. ACVIM, a professor at the University of California, Davis, School of Veterinary Medicine, recently completed a study in which he and colleagues, with support from colleagues at Merck Animal Health, sought to better understand EHV-1 prevalence in horses with signs of upper respiratory tract infection. He presented the results at the 2015 American Association of Equine Practitioners’ Convention, held Dec. 5-9 in Las Vegas.

Equine herpesvirus-1 causes varying clinical signs. In young horses it typically appears as a respiratory virus with clinical signs such as fever, lethargy, anorexia, mandibular lymphadenopathy (enlarged lymph nodes), and profuse clear nasal discharge. In adult horses EHV-1 can produce similar clinical signs, but it could also remain subclinical (meaning the horse shows no outward signs of disease), cause abortions in pregnant mares, or result in neurologic complications (a condition termed equine herpesvirus myeloencephalopathy).

In their recent study, Pusterla and colleagues sought to gain a better understanding of EHV-1 prevalence and epidemiology. They tested more than 4,000 voluntarily submitted nasal secretion and blood samples from equids with fever, signs of respiratory infection, and/or neurologic disease using qPCR, an assay that detects bacterial and viral DNA. The team also collected responses from a questionnaire regarding the horses’ background and clinical signs