Dog eats bat theory for coronavirus

THE global coronavirus pandemic may have started after a stray dog ate bat meat, a study has indicated.

Feral canines are the most likely animal intermediate host for the transmission of Sars-CoV-2 into humans, suggested Professor Xuhua Xia after studying coronavirus signatures across different species. He hypothesises that the ancestor of the new coronavirus and its nearest relative, a bat coronavirus, infected the intestines of dogs, where it evolved before jumping to humans.

The findings of Prof Xia, from the University of Ottawa’s biology department, are published online in the advanced access edition of the journal Molecular Biology and Evolution.

Humans and mammals can fight viruses through a key antiviral protein called Zap which prevents the infection from multiplying, while regions of DNA called CpG dinucleotides direct the immune system to attack the virus.

But single-strand coronavirus can avoid the body’s natural defences by reducing CpG, in a similar fashion to HIV.

In his study, Prof Xia analysed all 1,252 full-length betacoronavirus genomes deposited into the open access GenBank database.

He said that Sars-CoV-2 and its closest known relative, a bat coronavirus (BatCoV RaTG13), which shares 96% sequence similarity, have the lowest amount of CpG among its close coronavirus relatives.

Only genomes from canine coronaviruses, which have already caused a highly contagious intestinal disease worldwide in dogs, have similar genomic values, according to the study.

Dogs also have coronaviruses which affect their respiratory systems as well as their digestive systems, but the digestive kind has much lower CpG values, the paper notes.

The cellular receptor for Sars-CoV-2 entry into the cell is called ACE2, which is “pervasively expressed in the human digestive system ... with relatively low expression in the lung”, the study says.

It adds: “The interpretation is further corroborated by a recent report that a high proportion of Covid-19 patients also suffer from digestive discomfort.

“In particular, live Sars-CoV-2 virus was isolated from the stool of a Covid-19 patient. In this context, it is significant that BatCoV RaTG13 ... was isolated from a fecal swab.

“These observations are consistent with the hypothesis that Sars-CoV-2 has evolved in mammalian intestine or tissues associated with the intestine.”