THERE are four possible scenarios, as to the origins of Covid-19, according to leading science at the World Health organisation (WHO).
The first suggests that the virus started out in an animal —probably a bat — that came into contact with a human. The virus, then, immediately began to spread to other humans.
The WHO report cites strong evidence showing that most coronaviruses that infect humans come from animals, including the virus that caused the SARS epidemic in 2003. Bats are thought to be the most likely culprits, as they host a virus that is genetically related to SARS-CoV-2.
The report acknowledges the possibility that the virus spread to humans from pangolins or minks. But David Robertson, head of viral genomics and bioinformatics at the University of Glasgow, says the WHO joint team sampled many animal species beyond bats for the report. The analyses points to bats as the reservoir species.
The says that second scenario scientists believe the more likely theory is that the virus first traveled through another animal, such as a mink or a pangolin. Unlike bats, these animals have regular contact with humans — particularly if they’re being raised on a farm or trafficked in the illegal wildlife trade.
If the virus jumped first to another animal, that might also explain how it adapted to be harmful to humans— although David Robertson says that the virus likely wouldn’t have had to change much. Genomic analyses suggest that SARS-CoV-2 is a more ‘general’ virus rather than one specifically adapted to humans, explaining why it can easily jump among pangolins, mink, cats, and other species.
The WHO report points out that this is the path that previous coronaviruses have taken to infect humans. The SARS virus, for example, is thought to have passed from bats to palm civets before causing a human epidemic in 2002. Meanwhile, the virus that causes MERS has been found in dromedary camels throughout the Middle East.
The third theory suggests the virus may have come to humans through frozen and refrigerated foods. The virus might have actually originated outside of China but was imported either on the surface of food packaging or in the food itself.
While such might have played a role in new outbreaks, scientists say there’s little reason to believe that it was the source of the pandemic. There’s no direct evidence that SARS-CoV-2 is responsible for foodborne outbreaks.
The most controversial hypothesis for the origin of SARS-CoV-2 is also the one that most scientists agree is the least likely: that the virus somehow leaked out of a laboratory in Wuhan where researchers study bat coronaviruses. Originally believed by Donald Trump and his administration, this theory suggests that perhaps a researcher was infected in the lab —accidentally or otherwise — or manipulated a coronavirus strain to create SARS-CoV-2.
Although there have been laboratory leaks in the past, the WHO report points out that they’re rare. The main evidence it cites to support this theory is the fact that researchers at the Wuhan Institute of Virology have sequenced the bat coronavirus strain as part of their effort to prevent zoonotic viruses from spilling over to humans.
But that’s just about the only evidence that supports this hypothesis. The WHO report says there is no record that any Wuhan laboratory was working with a virus more closely related to SARS-CoV-2 before the first cases of COVID-19 were diagnosed in December 2019.
How the coronavirus might have originated
