Two presentations at the International Conference on Equine Infectious Diseases yesterday discussed equine coronavirus and whether it might be a new or previously unrecognized cause of disease in adult horses. This follows a presentation the day before that mentioned coronavirus diarrhea in racing draft horses in Japan – a rather unique group, pictured at right.

Dr. Nicola Pusterla from the University of California Davis described five suspect outbreaks in boarding facilities from four US states. Seventy-three (73) horses were affected overall, with decreased appetite being the most common sign in affected horses, followed by lethargy, fever, soft manure and colic. Equine coronavirus was detected in the vast majority of sick horses but rarely from healthy horses at the same facilities. Most horses got better without specific treatment, but five horses died or were euthanized. Overall, the attack rate on farms was high but the death rate was low. Fortunately from an infection control standpoint, infected horses only shed the virus for a short period of time (a few days), making control easier.

Dr. Ron Vin followed this presentation with a description of coronavirus involvement in sporadic disease and outbreaks in adult horses from a variety of US states, most often with mild diarrhea and low white blood cell counts. As with the first report, disease severity was usually less than what we see with some other causes of diarrhea in adult horses, such as Salmonella and Clostridium difficile.

One thing that’s not clear is whether this virus is truly a cause of disease or something that’s just being found in horses that have some other undiagnosed disease. No other potential causes were identified in most of the suspected coronavirus infections, but a large percentage of cases of diarrhea that we see go undiagnosed because we don’t know all the possible causes. It’s certainly possible that there was another cause, but these results suggest that equine coronavirus is something for which we should be looking out when we see gastrointestinal (e.g. colic, diarrhea) or non-specific disease (e.g. off feed, lethargic with no other particular signs), especially during outbreaks. The story may be different in foals, since shedding of the virus by healthy foals isn’t uncommon.

Photo credit: