ADELAIDE, Australia — The origin of the coronavirus pandemic is a mystery scientists (and the public) are still trying to solve. Now, a revealing new study has uncovered concerning details about this virus’s makeup. While many believe COVID-19 first spread from animals to humans, new evidence shows the virus has been “well adapted to infect humans” from the start.
Scientists in Australia say they examined a computer model of SARS-CoV-2, the virus causing COVID-19, and compared how it infects humans and a collection of 12 domestic and exotic animals. These species include cats, dogs, cows, pigs, and some of the suspected origins of the pandemic — bats and pangolins.
Their study finds SARS-CoV-2 is actually more adapted to binding with and infecting human cells rather than bat or pangolin cells. More specifically, scientists already know that SARS-CoV-2 uses its “spike” protein to attach itself to the ACE2 receptor gene on the surface of cells; hijacking them to produce more of the virus. The new study shows the virus forms its tightest bonds with human cells, not animal cells.
Scientists explain that if the virus had come from one of these animals, they would expect to see SARS-CoV-2 form tighter bonds with their cells — not humans. The revelation is now raising even more questions and doubts about the theory COVID-19 originated in animals before spreading to humans.
“Humans showed the strongest spike binding, consistent with the high susceptibility to the virus, but very surprising if an animal was the initial source of the infection in humans,” says La Trobe University Professor David Winkler in a media release.
Is COVID-19 origin from animals?
The other is that the virus passed from bats to another species scientists haven’t identified yet and then spread to humans. Study authors note their new findings appear to rule out COVID spreading directly from bats to humans. They add that SARS-CoV-2 doesn’t actually attach itself to bat cells well at all.
“The computer modelling found the virus’s ability to bind to the bat ACE2 protein was poor relative to its ability to bind human cells. This argues against the virus being transmitted directly from bats to humans. Hence, if the virus has a natural source, it could only have come to humans via an intermediary species which has yet to be found,” explains Flinders University Professor Nikolai Petrovsky.
Could pangolins be the missing link?
One species of interest to scientists tracking down the origins of COVID is the pangolin. These rare ant-eaters live in South-East Asia and humans have occasionally used them as either food or medicine. The study shows SARS-CoV-2 binds tighter to the cells of pangolins than other animals, including bats, monkeys, and snakes.
“While it was incorrectly suggested early in the pandemic by some scientists that they had found SARS-CoV-2 in pangolins, this was due to a misunderstanding and this claim was rapidly retracted as the pangolin coronavirus they described had less than 90% genetic similarity to SARS-CoV-2 and hence could not be its ancestor,” Prof. Petrovsky says.
However, new findings reveal this different form of coronavirus still has an almost identical spike protein that binds to ACE2. If pangolins are the key, researchers say they still can’t rule out whether these changes happened naturally — or if someone made these changes in a lab.
“This sharing of the almost identical spike protein almost certainly explains why SARS-CoV-2 binds so well to pangolin ACE2. Pangolin and SARS-CoV-2 spike proteins may have evolved similarities through a process of convergent evolution, genetic recombination between viruses, or through genetic engineering, with no current way to distinguish between these possibilities,” Prof. Petrovsky reports. “Overall, putting aside the intriguing pangolin ACE2 results, our study showed that the COVID-19 virus was very well adapted to infect humans.”
“We also deduced that some domesticated animals like cats, dogs and cows are likely to be susceptible to SARS-CoV-2 infection too,” Prof. Winkler adds.
The findings appear in the journal Scientific Reports.