Outbreaks of the neurologic form of equine herpesvirus-1 (EHV-1) have caused great financial and equine losses in recent years. These cases have solely affected horses, with no reports in the literature of any mules or donkeys showing clinical signs. Some of these equids have, however, shown evidence of antibodies against EHV-1 in their blood, prompting a group of researchers from the University of California (UC), Davis, to evaluate the role mules might play in EHV-1 spread.

Nicola Pusterla, DVM, PhD, Dipl. ACVIM, a professor in the Department of Medicine and Epidemiology at UC Davis, shared the results at the 2012 International Conference on Equine Infectious Diseases, held Oct. 21-26, in Lexington, Ky.

"The aim of this study was to investigate the role of mules as possible silent shedders during an outbreak of EHM (equine herpesvirus-1 myeloencephalopathy) occurring at a packing station in northern California (in September 2011)," he explained.

During that outbreak, veterinarians performed physical and neurologic evaluations and collected blood samples and nasal secretions for quantitative PCR (polymerase chain reaction, a type of DNA test) and serological detection of EHV-1 from 82 horses and 59 mules. Fifty-six of these animals (39.7%) tested PCR positive for EHV-1