A relatively new equine pathogen on the scene called coronavirus causes gastrointestinal illness, but not in every horse that has it. And because it bears some similarities to its viral cousin, bovine coronavirus, which in cows causes mild respiratory signs in addition to the gastrointestinal ones, equine researchers wondered if there’s a subset of horses getting a respiratory form of the virus, and, if so, could it present a diagnostic opportunity.

Nicola Pusterla, DVM, PhD, Dipl. ACVIM, a professor at the University of California, Davis, School of Veterinary Medicine, and colleagues conducted a study to find out if equine coronavirus (ECoV), which can be detected in infected horses’ feces, can colonize horses’ respiratory tracts and, as such, be isolated from their nasal secretions. So. He presented their results at the 2015 American Association of Equine Practitioners’ Convention, held Dec. 5-9 in Las Vegas.

Common signs of ECoV infection in adult horses include anorexia, lethargy, and fever; less common signs include diarrhea, colic, and neurologic deficits. Infected horses can develop complications, including septicemia (infection in the bloodstream), endotoxemia (endotoxin), and encephalopathy (brain disorder, in this case caused by abnormally high ammonia levels in the blood), all of which are associated with gastrointestinal tract (enteric) barrier breakdown. Many infected horses develop illness, but few die as a result, and the disease often resolves on its own.

Pusterla said ECoV is closely related to bovine coronavirus, which can cause both respiratory and enteric disease. He and colleagues wondered if ECoV might also have a tendency to gravitate to respiratory tracts and, thus, be present in nasal secretions.

To find out, the team took nasal secretion samples from 2,437 horses with acute onset fever and/or respiratory signs and tested them for ECoV and other common respiratory pathogens using qPCR, an assay that detects bacterial and viral DNA. Using the results, they also looked for associations between the presence of ECoV and other observations (such as the patient’s age, sex, clinical signs, etc.).

Key findings included:

  • The team found ECoV in just 17 samples—less than 1%;
  • Nine of those 17 horses also tested positive for other respiratory pathogens, such as equine herpesvirus-4 (EHV-4), equine influenza virus (EIV), equine rhinitis B virus (ERBV), and Streptococcus equi spp equi (the bacterium that causes strangles);
  • The most common clinical signs in ECoV-positive horses were nasal discharge, fever, lethargy, anorexia, and cough;
  • The team did not identify any statistically significant associations between the presence of ECoV and horse age, breed, sex, use, specific clinical signs, or the presence of co-infections; and
  • The team saw a “higher-than-expected prevalence” of coronavirus-positive horses that also tested positive for rhinitis B virus than they saw ECoV-negative horses testing positive for ERBV.

In the end, Pusterla and colleagues found low detection rates of ECoV in nasal secretions from horses with fever and signs of respiratory disease. He said further research is needed to determine whether ECoV can, in fact, colonize horses’ upper airways and cause disease.

He said he hopes to evaluate the overall seroprevalence of ECoV in healthy adult horses in the United States in the future.

“The detection of ECoV in nasal secretions from horses with fever and/or acute onset of upper respiratory signs is an infrequent event,” Pusterla said. “From a practical standpoint, the testing for ECoV should be restricted to feces from horses with fever, lethargy, anorexia, colic and diarrhea and not necessarily include horses with upper respiratory tract signs.”