By Katherine Dillinger, CNN
Two preprint studies published on Saturday offer further evidence that the coronavirus originated in animals and spread to humans in late 2019 at the Huanan Seafood Market in Wuhan, China.
One of the studies – neither of which has been peer-reviewed or published in a professional journal – used spatial analysis to show that the earliest known cases of Covid-19, diagnosed in December 2019, were market-centric . The researchers also report that environmental samples that tested positive for the virus, SARS-CoV-2, were strongly associated with live animal sellers.
The other study indicates that the two main viral lineages were the result of at least two events in which the virus crossed species into humans. The first transmission most likely occurred in late November or early December 2019, the researchers said, 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 origins or of a leak. Many of the researchers behind the new studies also took part in a review published last summer that indicated the pandemic almost certainly originated in an animal, likely at 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-related (or zoonotic) origins, Michael Worobey, Professor and Head 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 was born in a lab. “It’s not something that makes sense anymore to imagine that it started any other way.”
Worobey compared the initial spread pattern of the coronavirus to a firework display, with the market at its center. The explosion began in late 2019, but the pattern had completely changed by January or February 2020, the mark of a virus “seeping into the local community”.
The study notes that “December 2019 Covid-19 cases were unexpectedly geographically distributed near and centered on the Huanan market, whether or not they worked, visited, or were knowingly linked to someone. one who had visited this market in late 2019. Furthermore, among these cases epidemiologically linked to the market, the overwhelming majority were specifically linked to the western part of Huanan market, where most of the live mammal vendors were located.
When researchers tested surfaces on the market for genetic material from the virus, there was a stand with the most positive ones, including in a cage where a researcher had previously seen mammals called raccoon dogs being kept.
The results are “as close as you can get to having the virus in an animal,” Robert Garry, professor of microbiology and immunology at Tulane Medical School, told CNN.
Garry was co-author of the study which found at least two zoonotic or animal transmission events. He notes that the pandemic started with two major viral lineages, called A and B, although there are likely even more forms of the virus “that failed to establish themselves in humans.” The B line is the more common of the two and the only one that had previously been found in the market, but the study indicates that the A line was also circulating in the region at the start of the epidemic.
The virus most likely started in at least two animal transmissions, with a raccoon dog or other mammal serving as an intermediate host before spreading to humans, according to the study.
Taken together with reports of SARS-CoV-2 infection in animals like big cats, deer and hamsters, this shows that “this is a virus that just doesn’t care what it gets into. replica,” Garry said.
Garry and Worobey say studies show the urgent need to pay attention to situations in which animals and humans interact closely on a daily basis. “We need to do a better job of breeding and regulating these wild animals,” Garry said, and “investing in infrastructure where the viruses are spreading.”
Worobey also said human surveillance is crucial to preventing future pandemics, adding that experts and officials should better detect cases of respiratory disease without a clear cause, isolate patients and sequence viruses. “It’s not the last time this will happen,” he said.
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