A new analysis of genetic material collected at a live animal market in Wuhan in the early weeks of the COVID-19 pandemic strengthens evidence that the outbreak occurred when the coronavirus jumped from infected animals to humans, scientists said.
In RecommendationsThe findings, Cell reports, do not identify any specific infected animal that carried the SARS-CoV-2 virus to a Chinese city of more than 11 million people. And they do not conclusively prove that the Huanan wholesale seafood market is at zero due to the pandemic. More than 7 million people died.
But genetic evidence suggests the market meets the conditions for an outbreak, making it harder to explain how the coronavirus could have emerged from a lab, a farm or even the city’s four live animal markets, the study’s authors said.
“It’s like the gorilla virus appeared in San Diego and first affected people who worked at the San Diego Zoo and lived nearby and then spread more widely,” he said. Michael Vorobeyevolutionary biologist at the University of Arizona who worked on the study. “It’s not a stretch to think that it probably came from the gorillas at the zoo.”
The true cause of this pandemic has been debated since the early days of its emergence. Wuhan is home to a government laboratory where scientists study coronaviruses similar to SARS-CoV-2, which led to the politiciansnational security experts, late talk show hosts and many scientists, including Vorobey, are wondering whether the virus came from a laboratory.
Although this argument may be interesting, there is no hard evidence to support the leak hypothesis. In the meantime, more information has come in. convinced the scientists with experience in relevant fields where the virus that causes COVID-19 is found in animals, such as the viruses that cause SARS, MERS, and influenza.
The new results continue this trend, he said. Dr. Dominic Dwyermember of the international delegation investigated the origin of the pandemic for the World Health Organization.
“You put all these hypotheses about origin on the table and as the evidence comes in, some of them are getting stronger,” said Dwyer, a physician and virologist at the University of Sydney and Westmead Hospital in Australia who was not involved in the latest work. . . “This paper provides more evidence to support the origin of the animals through the Huanan market.”
The analysis published Thursday is based on genetic data from hundreds of samples collected in and around the Huanan market by researchers at the Centers for Disease Control and Prevention shortly after the market closed on Jan. 1, 2020. They said they detected the coronavirus in 74 environmental samples they analyzed. report last year in the journal “Nature”.
Vorobei and his colleagues dug deeper into this data. Using two different genetic techniques, they looked for fragments of SARS-CoV-2, as well as animal and human DNA.
They then plotted what they found on a map of the expanding market, allowing the team to imagine how a few initial infections could escalate into a global health emergency.
Among the 585 samples collected in early January 2020, those containing the coronavirus were collected in the southwestern part of the market. It was a place where wild animals were kept in cages for sale.
“The market spans several acres and extends into one corner of the market and into several stalls,” Dwyer said. “It’s consistent with where the animals came from. If it was coming from people wandering around the market, you’d find it everywhere.”
A “refurbished” market stall, the study authors wrote. It had evidence of SARS-CoV-2 in many places: on at least one cart, in an iron container, on the floor and on a machine used to clean hair and feathers. The researchers have dubbed it “wildlife tent A.”
Another 60 samples were taken from the market’s drainage system in late January 2020. Researchers found genetic evidence of the coronavirus in four of them, including one near a pet store in A.
This drain tested positive for SARS-CoV-2 as early as mid-February. The researchers wrote that two drains downstream were likely contaminated with water from Wildlife A’s ditches.
The samples from the store that contained the coronavirus also contained DNA from a variety of animals, including dogs, rabbits, tall bamboo rats, Malayan porcupines and palm-masked civets. The most abundant DNA came from raccoon dogs, and some was found on a nearby garbage cart, which also tested positive for the virus.
The closest living relatives of SARS-CoV-2 are the circulating coronaviruses in the horseshoe in southern China, Laos and Vietnam and in pangolins from southern China. But no bat or pangolin DNA was found in any samples from the Huanan market.
Raccoon dogs, masked palm civets, tall bamboo rats and Malayan caterpillars transferred before the coronavirusesthe authors of the study pointed out. Could they do it in Wuhan?, they asked.
Security guards stand outside the closed Huanan Seafood Wholesale Market in Wuhan on January 11, 2020.
(Noel Celis/AFP via Getty Images)
It is not known whether bamboo rats or Malaysian porcupines can be infected with SARS-CoV-2, the study authors wrote. There is no clear evidence that palm-masked civets can contract the virus, but cell lines from the animals have been shown to be susceptible. in laboratory experiments.
On the other hand, raccoon dogs are known Capturing and transmitting SARS-CoV-2. And they were the most abundant animals in A.’s wildlife store.
Researchers looked deeper into the raccoon dog’s DNA to see if they might have come from southern China, where they interbred with bats. They couldn’t say, but they were able to rule out a connection with raccoon dogs living on fur farms in northern China.
Worobey and colleagues also studied animal viruses other than SARS-CoV-2 detected in pet stores to see if they provided information about the origin of infected animals.
The kobuvirus that infected civets at the Huanan market was related to a virus found in animals sold in Sichuan and Guangxi provinces, which are closer to the range of horseshoe and pangolin rats. And a betacoronavirus that infected bamboo rats had a close relative in a bamboo rat farm in Guangxi, one of two southern provinces where market vendors were known to bring the animals.
“These findings suggest that the transport of some infected animals from southern China to Wuhan, a commercial channel, may also have triggered the emergence of SARS-CoV-2,” the study authors wrote.
Achieving this will require more work, including fieldwork to collect animal samples in China, he said. Florence Debarreevolutionary biologist at the French National Centre for Scientific Research in Paris and lead author of the study. Worobey said he plans to continue that line of research.
Dwyer praised the effort to identify animals in the market and, by extension, how the virus could enter the market.
A second line of evidence also supports the hypothesis that the pandemic had a so-called zoonotic origin, the scientists said.
Among the samples collected at the Huanan market on January 1, 2020, researchers were able to identify four nearly complete SARS-CoV-2 genomes. One of them is from the so-called A lineage and the other three are from closely related B lineages.
Investigators could not say whether the virus was transmitted by animals or humans, but the surname Munanae was obtained from a store where a worker sought medical care in mid-December 2019. Although this was the week before COVID-19 was recognized as a disease, a World Health Organization report later described the worker as a suspected patient.
Confirming the presence of both strains in the market allowed the team to compare their genomes and work backwards to figure out when the two strains diverged and what their most recent common ancestor was. They came up with six candidates, some of which are more credible than others.
There was a 99% chance that one of the four possible candidates was correct, and all four had one important thing in common: They were “either the same or identical” to the last common ancestor of the pandemic as a whole, the study leader said. Alexander Krits-ChristophFreelance computational microbiologist.
The study’s authors said they expect that if the surge in the Huanan market begins, the infected animal or animals entered the market in November or early December. The virus then spread among animals kept in close quarters and also among their humans. These conditions allowed the virus to establish itself among humans and spread among its new hosts in a densely populated city.
On the other hand, it is becoming more difficult to fit all these facts into a coherent story that the coronavirus entered China through imported frozen food (as the Chinese government has claimed) or escaped from a virology lab with biosafety protocols (as some have suggested by members of the US intelligence community), Dwyer said.
“We are not adding anything to support the lab leak or frozen food theories,” he said. “This just continues to reinforce the animal and market hypothesis.”
Given that the pandemic began in a city that is home to a virology lab where scientists are studying the coronavirus, it raises the question of whether this is more of a coincidence and whether incriminating evidence is being covered up, DeBarre said.
“A lot of us were very open to the idea,” he said. “But then the data piled up and everything was pointing in the same direction: everything was pointing to the market.”
“In science, you rarely have definitive answers,” he said. “You say, ‘Given all the information we have, this seems the most likely interpretation.’
