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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28 January 2019 The Horse | TheHorse.com multiplying on their own, viruses like ECoV must invade a host cell (e.g., one lining the inside of a horse's gastrointes- tinal tract), taking over its resources to divide and make more virus particles. Other examples of coronaviruses include severe acute respiratory syndrome (SARS-CoV), a sometimes-fatal human disease that might sound familiar from news reports in the early 2000s, and bovine coronavirus (BCoV), known for causing winter dysentery and respiratory disease in cattle. "Horses become infected with ECoV by ingesting the virus that was shed in the feces of another horse," says Scott Weese, DVM, MSc, Dipl. ACVIM, a professor in the Department of Pathobiology at the University of Guelph's Ontario Veterinary College, in Canada. He explains that a recent in-depth review on coronaviruses and how they cause disease reveals that once a horse ingests ECoV, the virus appears to travel to the small intestine, where it attaches to specific receptors on intestinal cells. It does so using proteins protruding from its outer envelopes—akin to the jewels on a crown. From there, the virus particle fuses with the host's cell, and the RNA enters the host cell and integrates itself into that cell's DNA. The virus then uses the host cell's resources to replicate, mak- ing thousands more disease-causing virus particles. Nicola Pusterla, DVM, PhD, Dipl. ACVIM, has dedicated years to studying this pathogen (disease-causing organism). A professor in equine internal medicine in the University of California, Davis, Department of Veterinary Medicine and Epidemiology, he says that "ECoV is a rel- atively newly recognized disease affecting the enteric system of adult horses. Since 2010, when the ECoV test was developed, outbreaks of ECoV have been diagnosed in Japan, Europe, and throughout most of the United States." Pusterla recently co-authored a study in which he and colleagues summarized their findings from examining 472 horses involved in 20 ECoV outbreaks from November 2011 to March 2017. Based on that data, he says these are the most common signs of illness associated with ECoV infection in adult horses: Clinical Sign of ECoV Percentage of Affected Horses Showing These Signs Anorexia 97 Lethargy 88 Fever (range, 101.5-106°F; median, 103.8°F) 83 Soft, watery feces 23 Colic 19 Encephalopathy (circling, head- pressing, seizures) 3 He notes that only 130 of the 472 study horses that tested positive for ECoV displayed clinical signs of disease. In fact, an estimated 4-83% of affected horses remained healthy, meaning they showed no clinical signs of disease despite tests identifying ECoV in their feces. "We estimate that only about 20% of horses that become infected with ECoV and test positive will show any of the above-described clinical signs of disease," says Pusterla. Horses that do develop clinical signs most often respond to basic support- ive care, usually involving fluids and non- steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone or flunixin meglumine. It's uncommon for horses to die from the disease, but when they do it's typically due to disease com- plications rather than the primary infec- tion, says Linda D. Mittel, MSPH, DVM, senior extension associate at Cornell University's Animal Health Diagnostic Center (AHDC), in Ithaca, New York. "One potentially serious fatal compli- cation is called hyperammonemia," she says. "This causes mild to severe neuro- logic conditions due to excess ammonia production in the bowel. This occurs due to a change in the bowel bacteria, called the intestinal microbiome, that produce high levels of ammonia that get absorbed into the bloodstream and circulate throughout the body, including the brain." Mittel adds that some owners call coro- navirus infection the lying-down disease. "Even though the horses are not usually severely colicky, they often are found down and just not quite right," she says. Risk Factors for ECoV Infection Pusterla's current data show that ap- proximately 2-6% of horses suspected of infection ultimately test positive for ECoV. This makes ECoV a seemingly in- significant condition; however, the num- ber of affected horses identified annually has increased over the past eight years. Pusterla and colleagues suggest this re- flects increased recognition of ECoV and owners' willingness to test for it. Moreover, after testing 5,250 apparent- ly healthy horses from 18 states, Pusterla reports the horses most at-risk for ECoV: ■ Reside in the Midwestern U.S.; ■ Are draft horses; and ■ Participate in ranch work/farming or NEW ARRIVAL: EQUINE CORONAVIRUS ISTOCK.COM Coronaviruses are so named because they look like they're wearing crowns when viewed under a microscope.

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