Evidence of stray dogs as possible origin of COVID-19 pandemic

Since the COVID-19 was first detected, virologists work against the clock to complete the full history of SARS-CoV-2. It is a crucial detective job not only when developing a vaccine, but also to prevent future infections. That task is to examine the genetic sequence of SARS-CoV-2 and compare it to that of other known coronavirus species.

Analysis suggests that the virus is a cross between a bat-related coronavirus and another coronavirus whose origin remains unknown. The two came together in a process called recombination, but the second ingredient in that genetic cocktail is still missing. Early studies pointed out that the virus causing COVID-19 passed from bats to snakes. It made sense when you consider that snakes are raised and sold in China for food and that the earliest cases pointed to a live animal market in Wuhan.

The snake hypothesis was eventually dismissed in favor of another species known to be a reservoir of coronavirus and the extensive illegal trade in it in China: the pangolin. A team of Chinese researchers discovered two other variants of the coronavirus 85.5% and 92.4% similar to the current cause of the pandemic in frozen pangolin remains that were seized by customs authorities in late 2018 and early 2019. The remains, however, have not served to trace the SARS-CoVID-2 pandemic to its origin.

A new study by the University of Ottawa (Canada) and published by Molecular Biology and Evolution propose a new hypothesis about the origin and initial transmission of the current coronavirus ―COVID-19―.

In this way, the study suggest stray dogs, especially the tissue of their intestines, may have contributed to the evolution of a SARS-CoV-2 parent ―neither pangolin nor snake, as previously thought―. The ancestor of SARS-CoV-2 and its closest relative, a bat coronavirus, infected the intestine of canids, which most likely resulted in a rapid evolution of the virus in canines and its spread to humans ―the licking of anal regions in canids during mating and other circumstances facilitate viral transmission from the digestive system to the respiratory system―.

To perform the study, authors examined 1,252 Betacoron virus genomes deposited in the GenBank gene sequence database. In their analysis, they found that SARS-CoV-2 and its closest known relative, a bat coronavirus (BatCoV RaTG13), are those with the least amount of CpG ―regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases―. Then, authors also examined the data from dogs, and found that only the genomes of canine coronaviruses (CCoV), which had caused highly contagious intestinal disease in dogs worldwide, have CpG genomic values similar to those seen in the SARS-CoV-2 and the BatCoV RaTG13.

For this reason, authors point to the need to include wild dogs in virus surveillance programs.

Link to the paper: https://doi.org/10.1093/molbev/msaa094

Editorial Disclaimer: information published during the 2020 COVID-19 pandemic may be updated frequently to reflect the dynamic nature of current understanding.

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