UTA biologists: COVID-19 virus originated in bats, not dogs

Todd Castoe, associate professor of biology at The University of Texas at Arlington

Todd Castoe, associate professor of biology at The University of Texas at Arlington, has co-authored two papers regarding the COVID-19 virus and its origins.

The first study, “Viral CpG deficiency provides no evidence that dogs were intermediate hosts of SARS-CoV-2,” was published in the July 13 edition of the journal Molecular Biology and Evolution. It disputes the findings of an earlier study from another research group claiming that the coronavirus may have jumped from dogs to humans.

The second is a study titled “Evolutionary origins of the SARS-CoV-2 sarbecovirus lineage responsible for the COVID-19 pandemic,” which was published in the July 28 edition of the journal Nature Microbiology. It reconstructs the evolutionary history of SARS-CoV-2, the virus responsible for the global COVID-19 crisis.

Blair Perry, a Ph.D. student in Castoe’s lab, is among the co-authors of both papers.

No evidence for dogs as intermediate hosts

Castoe and David Pollock, professor of biochemistry and molecular genetics at the University of Colorado, are co-first authors of the Molecular Biology and Evolution academic paper and were joined by an international team of collaborators. The paper refutes an earlier study that concluded the coronavirus may have made the leap from dogs to humans.

“Considering the ramifications, scientists need to be particularly careful in interpreting findings and avoid rushing to conclusions that are not well-supported by solid evidence,” Castoe said. “We need to get this right.”

Scientists around the world are interested in the origins of the novel coronavirus. They want to know which host the SARS-CoV-2 virus came from before it made the leap from animal to human.

Castoe and his colleagues said that although the recent origin of SARS-CoV-2 is uncertain, the best current evidence suggests that it was passed to humans by horseshoe bats or possibly pangolins, a kind of scaly anteater found in China. There is strong evidence that the virus has recently jumped between these animals or other intermediate hosts and humans.

The proposition that dogs were likely recent ancestors of SARS-CoV-2 is not justified by the available evidence, the researchers concluded. Dogs are not more plausible than most other potential host species and, based on current data, are far less plausible than bats or pangolins, they noted.

“Given the severity of the COVID-19 pandemic, it is easy for speculative or weakly supported findings to be blown out of proportion and over-interpreted,” Perry said. “With how quickly things are moving, such findings may then be used to make decisions on efforts to manage the ongoing pandemic and cause resources and efforts to be wasted by ‘barking up the wrong tree.'”

Evolutionary origins of the virus

In the Nature Microbiology study, researchers traced the evolutionary history of the SARS-CoV-2 virus and discovered that its genetic lineage has been circulating in bats for decades and likely includes other viruses with the ability to infect humans. Their findings could help prevent future pandemics that stem from this lineage.

“Understanding the origins of SARS-CoV-2 is a major priority because it may provide evidence for how and why this virus was transferred to humans, and how similar transfers to humans may be prevented in the future,” Castoe said.

The team included scientists from the United States, Belgium, United Kingdom and China. They learned that the lineage of viruses to which SARS-CoV-2 belongs diverged from other bat viruses somewhere between 40-70 years ago.

One trait that SARS-CoV-2 shares with its relatives, the team found, is the receptor-binding domain located on the viral spike protein, which allows the virus to recognize and bind to receptors on the surfaces of human cells.

The researchers concluded that the existing diversity and the recombination process among viruses in bats show how difficult it will be to identify viruses with the potential to cause major outbreaks in humans before they emerge. They state that effectively preventing future pandemics will necessitate better sampling in wild bats and the implementation of human disease surveillance systems that can quickly identify novel pathogens in humans and make real-time response possible.

Effective surveillance is predicated on knowing which viruses to look for and prioritizing those that can infect humans, they noted.

Funding for the research was provided by the Medical Research Council, the European Research Council, the Research Foundation–Flanders, and the National Natural Science Foundation of China.

– Written by Greg Pederson, College of Science

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