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UA researcher reveals COVID leaped to human hosts in Wuhan market

University of Arizona Prof. Michael Worobey and a team of scientists have found more evidence that COVID-19 originated in a Wuhan market and likely crossed over into two human hosts instead of just one.

Worobey co-authored a study published Tuesday on the virus' genetic origins and was a lead author on a second article that pinpoints the Huanan Seafood Market in Wuhan, China, as the “early epicenter” of the virus.

Findings from the local virus evolution expert and his fellow researchers largely rule out the lab leak theory that rose to popularity in the United States. However, the findings published by the journal "Science" stop short of pointing to the type of animal that humans received the virus from, although researchers suggest it could have been farm animals exposed to bats, rather than the early widespread popular idea of human-bat contact.

Worobey, UA's head of ecology and evolutionary biology, spoke about the findings at a Tuesday morning press conference along with three other researchers, including Kristian Andersen, a Scripps Research professor.  

Early indicators as to COVID's origin pointed to infected animals being sold at places like wet markets, similar to the SARS outbreak in the early 2000s, Andersen said.

“And that of course, presented the question, ‘But is it the market?’ he said. “And what these two papers show is really a yes, it very much points to this single market, not multiple markets here, but the single market.”

The first paper, which zeroed in on the market in the Chinese city, utilized data from a joint-report between the World Health Organization and Chinese researchers. With this data, scientists managed to map out more than 150 cases of the more than 170 people reported as infected in Hubei Province from December 2019.

They found an extremely high density of cases around the seafood market, even among people whose links to the shopping area are unknown. The study also indicates that both of the original COVID-19 sublineages, A and B, stemmed from the market in November 2019 and then spread into the surrounding area.

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The lab leak theory holds that the pandemic began after the virus escaped from a Chinese laboratory, and was flirted with by prominent Republicans such as Arkansas Sen. Tom Cotton. Some Democrats early on dismissed the theory that the virus spread to humans from a wet market for different reasons, saying the claim was anti-Chinese.

The lab leak idea will never be completely disproven, but the idea is not plausible, Andersen said. He said that early on he supported the theory, but no longer does, saying the two studies are the strongest evidence to date against the possibility that the pandemic began with a virus in a lab.

“It's not a formal proof again, but it is so strong, in my opinion, that any other version, the lab leak for example, would have to be able to explain all this evidence,” Andersen said. “And in my view, which has been my view for a very long time now, it's just not possible.”

The second study presented evidence that COVID-19 spilled over into humans more than once before spreading worldwide. Variant A of COVID was closer genetically to bat coronaviruses, whereas variant B appeared to be spreading in people earlier, said Joel Wertheim, a co-author of both studies.

Through genetic analysis and simulations of similar viruses spreading, scientists found variant A could not have mutated into variant B or vice versa, said Wertheim, an associate professor at the University of California - San Diego. Wertheim was joined by graduate student and co-author Jonathan Pekar at the news briefing.

Despite the seeming unlikelihood of a “once in a generation event” occurring twice in a small time period, it’s very possible, Wertheim said.

“But once all the conditions are in place, that is a zoonotic virus capable of both human infection and human transmission that is in close proximity to humans,” he said. “The barriers to spillover have been lowered, such that multiple introductions, we believe, should actually be expected.”

The paper also indicated that there may have been up to 24 introductions of COVID-19 from animals to humans before the two successful transmissions, Wertheim said. 

The scientists remain confident in their findings despite the studies being assisted by Chinese researchers. UA's Worobey said China is not a fan of the lab leak theory nor market theory. He said he received criticism from a Chinese authority for his support of the market-origin theory.

“The Chinese (authorities) are not fans of a lab leak theory, and they are not fans of the idea that this virus emerged from the wildlife trade at the Huanan market,” Worobey said.

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Chinese scientists helped improve gene sequences, Wertheim said.

“From a genomic perspective, the data that came from China looks like the data that came from everywhere else in the world, and there's no inconsistency there,” he said. “So I have no reason to doubt the veracity of the genomic data produced by Chinese scientists.”

Exact origin remains unknown

Researchers stopped short of pointing to a particular animal as the origin of the crossover on Tuesday.

Further international collaboration is needed to determine which animals at the market passed the virus on to humans, Andersen said. Raccoon dogs, which were found to be infected during the previous SARS epidemic, are one possibility, however other animals like deer and badgers were also being sold, he said.

The original A and B variants likely did not come from the same animal, Wertheim said. It’s a “very likely” scenario that a farm animal or animals were infected with COVID before reaching the market, Worobey said.

“A bat may have pooped on one of these animals in one of these farms, starting an outbreak in just one of these farms, shortly before the pandemic began,” he said.

Despite all that researchers have uncovered about COVID-19, the world is not ready for another pandemic like it, Andersen said. He said better transparency and quick data reporting will be needed in the future along with surveillance of things like wastewater for pathogens.

“And I will make it clear though that in terms of our ability to do that, I don't actually think we are doing better currently, than we are at the beginning of the pandemic,” he said. “Because, again, we downplay the risk of these infectious diseases, we don't really collaborate when trying to (go) against the same goals here.”

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University of Arizona News

Researchers, including the University of Arizona's Michael Worobey, published findings Tuesday that support the theory that COVID originated in a Wuhan market. The research also indicates that animals infected more than one human with COVID before human-to-human spread began.