Equine coronavirus is a relatively recently recognized infectious disease of adult horses. Its clinical signs of fever, lethargy, anorexia, colic, and diarrhea, however, can point to other diseases. This presents a diagnostic challenge for treating veterinarians. So what samples should a practitioner collect on a sick horse to confirm an equine coronavirus infection?
Nicola Pusterla, DVM, PhD, Dipl. ACVIM, professor of medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, attempted to answer this question during the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.
“Equine coronavirus makes liars out of horses,” he said, “particularly horses with fever, but no respiratory signs (nasal discharge, coughing) and no gastrointestinal signs (diarrhea, colic). What sample do you collect? It has you scratching your head.”
To find out, Pusterla studied 277 horses from across the United States with acute fever and at least one other equine coronavirus clinical sign, but no colic or diarrhea. He used qPCR testing to look for viral DNA in feces and nasal swabs from each horse. He also looked at several other factors, including age, breed, use, history, and more. Pusterla found that:
- 20 (7.2%) horses tested positive on feces for equine coronavirus, four of which tested positive on nasal secretions, as well;
- Of these, 9% also tested positive for other respiratory pathogens (e.g., equine herpesvirus, influenza, etc.), but there were no statistically significant associations between comorbidities (concurrent infections);
- Draft horses were overrepresented (there was a higher proportion of them among the study subjects than would be expected) and six times more likely to test positive for coronavirus;
- Performance horses and those on farms with large equine populations were more likely to have coronavirus (five times and 2.7 times, respectively), which reflects the virus’ highly contagious nature, said Pusterla (horses contract it by inadvertently ingesting virus shed in the feces of an infected animal); and
- Coronavirus-positive horses did not frequently show signs of coughing or nasal discharge.
Pusterla said equine coronavirus’ main signs are subtle—anorexia, lethargy, and fever. And while the virus doesn’t consistently induce gastrointestinal signs such as colic or diarrhea, affected horses’ feces are the most reliable sample to test.
“Nasal detection is low and likely represents environmental contamination (breathing in equine coronavirus particles) through fecal shedding,” he said.
So if you see a horse in “standby mode” (lethargic, feverish), test his feces for equine coronavirus, particularly if he shows no evidence of nasal discharge, Pusterla said.