WAIT, IT'S BACON? NOT THE YELLOW MENACE?:

There is a growing body of evidence that points to a different origin story for Covid-19. We now know that none of the animals tested at the Wuhan seafood market tested positive and about a third of the initial set of reported cases in people in Wuhan from early December 2019 had no connection to the seafood market, including the first reported case 3 4 . And we also now know, thanks to the leak of an official Chinese report to the South China Morning Post that the actual first known case of Covid-19 in Hubei was detected in mid-November, weeks before the cluster of cases connected to the Wuhan seafood market were reported5.

Last week, scientists at the Scripps Research Institute published a genomic sequencing analysis of the SARS-CoV-2 virus in the journal Nature that raises more doubts about the possibility of SARS-CoV-2 having originated at the Wuhan seafood market6.

The scientists conclude that SARS-CoV-2 evolved from natural selection and not genetic engineering in a lab, and they say that this natural selection occurred through two possible scenarios. One is that it evolved into its highly pathogenic form within humans. In this case, a less pathogenic form of the virus would have jumped from an animal to a human host and then would have evolved into its current form through an "extended period" of "undetected human-to-human transmission". Under this scenario, there is no reason to believe that the Wuhan seafood market had anything to do with the evolution of the disease, even if it is quite possible that an infected person at the market could have transmitted it to others.

The second scenario fits with previous coronavirus outbreaks, in which humans contracted deadly coronaviruses after direct exposure to civets, in the case of SARS, and to camels, in the case of MERS. In this scenario, SARS-CoV-2 would have evolved to its present form in an animal host before transfer to humans. Like many other scientists, the Scripps researchers think that it is most likely that the initial transmission would have occurred from bats to an intermediate animal host, where the virus then evolved to its current form.

The Scripps7 researchers go on to say that the particular genetics of SARS-CoV-2 indicate that "an animal host would probably have to have a high population density (to allow natural selection to proceed efficiently) and an ACE2-encoding gene that is similar to the human ortholog," which is what the SARS-CoV-2 virus binds to in humans.

So which animals fit this criteria?

Another recently published study identifies the most likely intermediate animal hosts for SARS-CoV-2, based on their presence in Wuhan and their having a human-like ACE2 that enables the binding of SARS-CoV-2. These are the animals the study identified: civets, pigs, pangolins, cats, cows, buffalos, goats, sheep and pigeons8.

Many of the animals on this list are industrially farmed in China, even wild animals like civets and pangolins are intensively farmed for their use in Chinese medicines. Suspicions that wild animal farms may have been behind the Covid-19 outbreak have already led the Chinese government to shut down 20,000 wild animal farms across the country9.

But hardly any attention has been given to some other animals on this list, which more clearly meet the "high population density" criteria. Pigs would be one obvious candidate from this list, for several reasons.

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