The Horse

JAN 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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TheHorse.com | The Horse January 2019 29 are used in breeding programs. "These horses appear to have the high- est chances of testing positive for ECoV," he says. "This was determined based on blood analysis or seroprevalence, which tests for the presence of antibodies against ECoV showing either current in- fection or previous exposure to the virus." Data from Japan also confirm that draft horses appear more susceptible to developing ECoV than other breeds, such as Thoroughbreds. "There's variation in reports of disease, but that may simply be testing bias," adds Weese. "We don't tend to see ECoV in Ontario, despite some testing, so I suspect there is still some true regional variation." The Importance of Diagnosing ECoV Equine coronavirus occurs in fewer than one in 10 horses, most cases remain free of clinical signs of disease, and most horses that do develop clinical infections typically recover uneventfully even with- out treatment. So why do we care about what appears to be a relatively benign viral disease? Further, why bother spend- ing money on testing rather than simply treating suspected cases if needed? "While there are no specific treatments for ECoV, a timely diagnosis can still be useful to exclude other causes that might have specific treatments, understand dis- ease trends, and guide infection control practices on the farm," Weese says. Just as you wouldn't take an equine herpesvirus outbreak lightly, don't treat ECoV outbreaks as benign. Like equine herpesviruses, ECoV is highly infectious, spreading rapidly between horses. Also similar to herpesviruses, apparently healthy horses can shed ECoV—a popula- tion referred to as inapparent shedders. "Further, if one considers the extensive list of colitis/enteritis (small intestine in- flammation) causes, the need for testing to discriminate between them is clear," says Weese. Causes of diarrhea in adult horses that can cause signs similar to ECoV include Salmonella spp; Clostridium difficile and Clostridium perfringens; Potomac horse fever; parasitism; antibiotic use; sand impaction; dietary imbalances; inflamma- tory bowel disease; and more. "Diarrhea is always a concern in adult horses because it can be severe and be- cause outbreaks can occur," says Weese. "Regardless of the underlying cause, the wall of the horse's colon can secrete large amounts of fluid and proteins into the intestinal tract. This results in loss of valuable electrolytes and nutrients from the intestinal content. "The inflamed wall also allows bacteria and their toxins that usually remain in the lumen of the intestine to gain access to the bloodstream, resulting in endo- toxemia," he adds. "These bacteria and toxins negatively impact various internal organs and can also contribute to compli- cations such as laminitis." The ECoV Test Several laboratories in the United States offer ECoV testing. "The test currently offered by our laboratory is referred to as a quantitative PCR test," says Mittel. "This test allows us to quickly detect even very small amounts of viral genetic material in the submitted fecal samples," which must be sent in by your veterinarian. Turnaround time for results is typically three business days Since 2013 the AHDC has received approximately 2,000 fecal samples for equine coronavirus testing. Of those, about 18% were ECoV-positive. Note, however, that horses can test negative during the very early stages of clinical disease because viral shedding peaks three to four days after clinical signs appear. "In other words, if a test is performed too early it may come back as a false negative," says Mittel. Weese also suggests not hanging your hat on testing alone. "ECoV testing is useful but may not have a large impact on case care—how the horse is treated—in sporadic cases," he says. "Testing for something like Sal- monella, where there are greater herd and public health implications, should also be performed." Preventing ECoV Infection Like many equine infectious diseases, particularly those caused by viruses, the most important strategy for avoiding in- fection is appropriate disease control and biosecurity strategies (TheHorse.com/ biosecurity-tips). "Standard strategies that would be used for any type of equine disease outbreak, such as equine herpesvirus outbreaks, are advocated," says Weese. "These include isolating all new horses Dr. Nicola Pusterla has dedicated years of his career to studying ECoV and has made significant strides in understanding the disease. COURTESY UC DAVIS

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