Equine Coronavirus: An Enteric Virus of Adult Horses
Equine coronavirus (ECoV) is classified within the Betacoronavirus genus, along with bovine coronavirus, porcine hemagglutinating encephalomyelitis virus, mouse hepatitis virus, rat coronavirus (sialodacryoadenitis virus), and certain human coronaviruses such as severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome coronavirus; the latter two viruses have caused epidemic outbreaks of respiratory disease in human beings in the last decade.
Equine coronavirus has been recently associated clinically and epidemiologically with emerging outbreaks of pyrogenic (fever-causing) and enteric disease in adult horses in Japan and anorexia, lethargy, and fever in the United States.
Coronavirus infection typically begins in the proximal small intestine and subsequently spreads to the colonic epithelial cells, leading to blunting of the intestinal villi and subsequent villous atrophy. Loss of epithelial cells results in malabsorption and maldigestion of nutrients and acute diarrhea.
Following a short incubation period of 48 to 72 hours, adult horses develop fever, anorexia, and depression. Changes in fecal character, ranging from soft-formed stools to watery consistency, and colic are seen in less than 20% of affected horses. A small number of horses develop acute neurologic signs due to hyperammonemia, which can manifest as severe depression, head pressing, ataxia, proprioceptive deficits, recumbency, nystagmus, and seizure. Common hematologic abnormalities are leucopenia due to neutropenia and/or lymphopenia. ECoV infection generally resolves within one to four days with supportive care consisting of the administration of anti-inflammatory drugs and oral or intravenous fluids. Fatalities have been associated with septicemia, endotoxemia, and metabolic abnormalities leading to encephalopathy (hyperammonemia).
Historically, the detection of ECoV has relied on either electron microscopy, antigen-capture ELISA, or viral isolation from the feces. All of these detection modalities lack sensitivity, especially if viral particles are not present in sufficient numbers. Quantitative polymerase chain reaction (PCR) assay for the detection of ECoV nucleic acid has supplanted many conventional virological assays, mainly due to its short turn-around-time, high throughput capability and increased analytical sensitivity and specificity. The overall agreement between clinical status and PCR results for ECoV is over 90%, making fecal PCR the diagnostic tool of choice.
Infected horses can shed ECoV up to 14 days. Due to the fecal-oral transmission route and the highly infectious nature of ECoV, common-sense biosecurity protocols should be instituted during an outbreak. ECoV-PCR-positive horses (clinical or subclinical) should always be isolated from the rest of the equine population to decrease the exposure risk and environmental contamination. Potentially exposed horses should not be moved until their definitive infection status has been determined.
For isolation purposes, use an empty barn or an isolation unit. In a barn situation, close one end of the barn and use it as isolation area. Caretakers and owners should wear gloves, protective clothing (coveralls or disposable gowns), and dedicated footwear. Good hand hygiene should be instituted (faucet with warm/cold water or hand sanitizer).
Barrier nursing techniques should be established in the form of footbath or mats in front of the isolation unit and each stall. This will minimize the spread of pathogens from stalls to clean areas. It is very important to control traffic and minimize contact of affected horses with the general public. Hygiene should be maximized by regular cleaning and disinfecting.
CONTACT—Nicola Pusterla, DVM, PhD, Dipl. ACVIM—firstname.lastname@example.org—530/752-1360— University of California Davis, California School of Veterinary Medicine Department of Medicine and Epidemiology
This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd’s, London.
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