Q. I’ve recently read two articles on TheHorse.com about coronavirus in horses (“What is Equine Coronavirus?” and “Coronavirus Recovery and Leaky Gut Syndrome”), which I’d never heard of before. Now I’m seeing news reports about coronavirus in humans in China, with cases now identified in the United States. I even read the disease is so serious its reporting has affected investment markets. However, I’m confused because the news is talking about a respiratory disease, while The Horse is describing a stomach bug. Is this the same disease that horses get, and is it contagious among different species?
A. The recent reports in the news media of cases of respiratory disease in humans in the P.R. China have linked these occurrences to infection with a previously undiscovered member of the coronavirus family. This family of viruses is so named because of their crownlike shape when visualized using an electron microscope. The virus is distinct from two other coronaviruses that also cause respiratory disease in humans: SARS (severe acute respiratory syndrome), which was first discovered in China in 2002, and MERS (Middle East respiratory syndrome), which was first identified in Saudi Arabia in 2012. These three viruses are very important human pathogens, highly contagious and capable of causing widespread disease and a variable mortality rate. Members of the coronavirus family also cause disease in certain domestic animal species, including horses (equine coronavirus infection), swine (transmissible gastroenteritis), cattle (winter dysentery), chickens (infectious bronchitis), and cats (reline infectious peritonitis) to name several.
Coronavirus infection in horses is a relatively recently recognized disease affecting the enteric (intestinal) tract of adult equines. A variety of outcomes have been reported following oral exposure of horses to equine coronavirus. Many experience only an asymptomatic (showing no clinical signs) infection. Others develop fever, diminished appetite, and a variable degree of depression, but no signs of enteric involvement. About 20% of infected horses develop signs of clinical disease, with soft feces and evidence of colic in certain individuals. Fewer than 5% of cases might exhibit signs of neurologic involvement believed to be attributable to hyperammonia in the enteric tract.
It’s evident from the foregoing that coronavirus infection in the horse is an enteric and not a respiratory disease. This is similar to coronavirus-related diseases in swine and cattle. The coronavirus that affects chickens, although primarily a respiratory pathogen, can also infect the urogenital and gastroenteric systems. Feline infectious peritonitis in cats is an immune-mediated disease. The primary clinical syndrome caused by members of the Coronavirus family will vary depending on the virus in question and the host species it infects.
It remains to be established whether the newly found human coronavirus can infect other species. It’s now known with respect to the two other important human coronaviruses (SARS-CoV and MERS-CoV) that each originated from bats, before jumping species and infecting the masked palm civet in the case of SARS-CoV and the camel in the case of MERS-CoV; the latter two species serve as intermediate hosts between bats and humans. It’s possible that the origin of the new human coronavirus may be similar. That said, current conjecture is also focusing on snakes (Chinese krait and Chinese cobra) sold at a local market in the Chinese city of Wuhan where the first cases were reported as a possible source of this virus infection for humans. Much remains to be done before we’re likely to determine the new human coronavirus’ origin.