By Katherine Dillinger, CNN
Two preprint studies released on Saturday provide further evidence that the coronavirus originated in animals and spread to humans at the Huanan Seafood Market in Wuhan, China, in late 2019.
One of the studies — none of which were peer-reviewed or published in a peer-reviewed journal — used spatial analysis to show that the earliest known Covid-19 cases, diagnosed in December 2019, were market-focused. The researchers also report that environmental samples that tested positive for the SARS-CoV-2 virus have been strongly linked to sellers of live animals.
The other study states that the two main viral lineages were the result of at least two events in which the virus species crossed into humans. The first transmission most likely occurred in late November or early December 2019, the researchers say, and the other lineage was likely introduced within weeks of the first event.
Experts have strongly condemned the theory of a laboratory origin for the virus, saying there is no evidence of such an origin or leak. Many of the researchers behind the new studies were also participants in a review published last summer that said the pandemic almost certainly started in an animal, likely a wildlife market.
The new studies take this area of research “to a new level” and are the strongest evidence yet that the pandemic had animal (or zoonotic) origins, said Michael Worobey, professor and chief of ecology and evolutionary biology at the University of Arizona, told CNN. Worobey was lead author of the geographic study and co-author of the other paper.
He called the results “game, set and match” for the theory that the pandemic originated in a lab. “It no longer makes sense to imagine that this started out differently.”
Worobey likened the pattern of the initial spread of the coronavirus to fireworks centered around the market. The blast began in late 2019, but the pattern had completely changed by January or February 2020, the hallmark of a virus “encroaching the local community.”
The study finds that “December 2019 Covid-19 cases were unexpectedly geographically close and concentrated in the Huanan market, whether they worked for, had visited, or were knowingly associated with someone operating that market late 2019. Furthermore, the overwhelming majority of cases epidemiologically linked to the market were specifically linked to the western part of the Huanan market, where most live mammal sellers were located.”
When researchers tested surfaces on the market for the genetic material of the virus, one stall had the most positive results, including one in a cage where a researcher had previously seen mammals called raccoon dogs being kept.
The results are “as close to having the virus in an animal as you can get,” Robert Garry, a professor of microbiology and immunology at Tulane Medical School, told CNN.
Garry co-authored the study, which found at least two zoonotic, or animal transmission events. It notes that the pandemic began with two major lineages of the virus, called A and B, although there were likely more forms of the virus “that have failed to establish themselves in humans.” Line B is the more common of the two and the only one previously found in the market, but the study says Line A was also circulating in the area early in the outbreak.
The virus most likely began with at least two animal transmissions, using a raccoon dog or other mammal as an intermediate host, before spreading to humans, the study said.
This, coupled with reports of SARS-CoV-2 infections in animals such as big cats, deer and hamsters, shows that “this is a virus that just doesn’t care what it replicates into,” Garry said.
Garry and Worobey say the studies show an urgent need to pay attention to situations where animals and humans interact closely on a daily basis. “We need to raise and regulate these wild animals better,” Garry said, and “invest in infrastructure in places where viruses are spilling.”
Worobey also said human surveillance is crucial to prevent future pandemics, adding that experts and officials should be better at detecting cases of respiratory illness without a clear cause, isolating patients and sequencing viruses. “This won’t be the last time this happens,” he said.
The CNN Wire
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