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They deny that the coronavirus originated in a laboratory 0:27
(CNN) - A gap in knowledge about the origins of the world's new coronavirus has provided fertile ground for all kinds of theories, from the fantastic to the dubious to the credible.
It is a biological weapon made by the Chinese. The US Army brought the virus to Wuhan. He leaked, like a genie from a bottle, from a laboratory in an accident. It took root in a wildlife market in Wuhan.
Scientists have joined across international borders to condemn nationalist-tinged conspiracy theories. And yet they are divided into what was once widely thought to be the most likely culprit: a so-called "wet market" in Wuhan, where wild animals are kept in cages and sold as pets or food. An animal infected with bats, perhaps a pangolin, is believed to have infected the first human.
The truth of how this started remains elusive. But CNN spoke to more than half a dozen virus experts about the origins of the outbreak, and they all say that anyone who claims to know the source of covid-19 is guessing. Scientists say there is no evidence that the Chinese or American government has purposely introduced the new coronavirus, SARS-CoV-2, into people.
To date, one thing seems likely: it came from bats.
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Experts disagree on wet market theory
It is "the simplest, most obvious and likely explanation," said Dr. Simon Anthony, a professor at Columbia University's Graduate School of Public Health and a key member of PREDICT, a federally funded program that investigates viruses in hosts. animals with pandemic potential. PREDICT has discovered 180 coronaviruses in a decade.
Although scientists rule out conspiracy theories about biological weapons, they are divided on other questions.
Experts disagree with the once widely accepted theory that the virus originated in a wet market.
Proponents believe that the bloody nature of these crowded markets filled with people and wild animals slated for slaughter makes them the most likely culprit; Those who hesitate cite a peer-reviewed study indicating that many of the earliest known patients had no direct exposure to the so-called wet market.
Another potentially explosive theory, first raised by two Chinese researchers in early February and amplified by Fox News presenter Tucker Carlson on March 31, argues that the origin dates back to an accident at one of the two laboratories near the market. from Wuhan who work with bats.
Most of the experts interviewed for this story dismissed the theory, whose authors allegedly withdrew their article, saying it was not supported by evidence.
The theory has also been vigorously denied by the Chinese government and one of the laboratories.
But an expert, professor of chemical biology and biological weapons expert at Rutgers University, has suggested to various media outlets that the theory of laboratory accidents has credibility.
"The possibility that the virus entered humans through a laboratory accident cannot and should not be ruled out," Dr. Richard Ebright told CNN in an email Sunday.
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Virus hunters target bats
In any case, the researchers agree that the coronavirus jumped from an animal to a human, a phenomenon known as "zoonotic overflow."
In early February, Chinese researchers published an article in Nature , a premier scientific journal, which concluded that "2019-nCoV is 96% identical genome-wide to a bat coronavirus."
Later that month, 27 public health scientists from across the United States and the world wrote a letter in The Lancet condemning conspiracy theories.
"Conspiracy theories do nothing but create fear, rumors, and prejudice that jeopardize our global collaboration in the fight against this virus," they wrote.
In the Lancet article, the experts cited scientific evidence supporting the theory that "it overwhelmingly concludes that this coronavirus originated in wildlife, like many other emerging pathogens."
One of those scientists is Peter Daszak, a preeminent virus hunter who has been working in China for 10 years.
"We are very confident that the origin of covid-19 is in bats," said Daszak, president of the EcoHealth Alliance, a nonprofit health organization that tracks zoonotic spread. "We just don't know exactly where it originated, what bat species exactly. And we don't know how many others there are that could emerge in the future. ”
It is a story of genetic detectives.
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Did you jump from bat to human or other animal first?
The researchers hope to track down the virus that is killing tens of thousands of a bat yet to be caught in the wild.
Another source of debate is whether the virus that causes covid-19 was transferred directly from the bat to humans, or whether there was an "intermediate" animal in between.
Daszak believes that a bat infected a farm animal that was brought to the market alive and kept with people in one of the most perfect incubators for viral infection - the Chinese wet market.
"The first time you come to China as a Westerner, it's kind of shocking to go to a wildlife market and see this huge diversity of animals live in cages on top of each other with a pile of guts that have been taken from an animal and lying on the ground, "he said. “As you walk to the stalls, you slip with the feces and blood. These are perfect places for viruses to spread. Not only that, people are working there ... children are playing there. Families almost live there. ”
Professor Andrew Cunningham of the Zoological Society of London says that wet markets are prime candidates for causing zoonotic wildlife propagation events, which he says have become more common in the past 30 years.
"If you bring wild animals, you catch them in the wild, you collect them in large numbers," he said. "They are stressed and then they can become virus factories, and they are in close contact with humans in the markets and are massacred in the markets and by people in relatively unsanitary conditions."
But an article in The Lancet has cast some doubt on the theory. The study shows that about a third of the first 41 confirmed infected patients had no direct exposure to the wet market. Among them was the first known patient, whose symptoms began to appear on December 1.
"No epidemiological link was found between the first patient and subsequent cases," the report states.
The market was closed on January 1, two days after Wuhan authorities issued a public health alert about it.
(An article in the South China Morning Post indicates the date of the first case as early as November 17).
"I think people who entered the fish market were already infected," Vincent Racaniello, a professor of microbiology at Columbia University, told CNN.
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Most experts reject the theory of laboratory leaks
Racaniello offers another theory: the source of the outbreak is a farmer.
"In bats, these viruses are intestinal viruses and are removing bat feces, what we call guano," he said. “And if you enter a bat cave, it is full of guano. And farmers in many countries harvest guano to fertilize their fields. "
Racaniello speculates that, after becoming infected, a farmer or associate went to Wuhan and started infecting other people.
"We know that in China you can eat bats, that's another scenario," he said. "But I don't think it's more likely that a farmer who harvests guano or a farmer who finds a bat in his stable."
Anthony, also from Columbia, echoed Racaniello's skepticism about the wet market theory.
"At the beginning of the outbreak ... everyone was talking about what had emerged from the wet market," he said. "And now I think the data questions whether that's really true."
Anthony noted that the mystery of the 2003 SARS outbreak isn't even solved.
For many years, it was widely believed that the SARS virus leaped from a bat into an intermediate host, a cat-like civet, that infected a person at a food market in China. But a 2013 study, backed by a follow-up in 2017, suggested that the 2003 coronavirus may also have jumped directly from a bat into a human.
"We don't know which of those is really true," Anthony said.
Perhaps the most forceful rejection of the wet market theory came from Ebright of Rutgers.
"It is absolutely clear that the market had no connection to the source of the outbreak virus and instead was only involved in amplifying an outbreak that had started elsewhere in Wuhan almost a month earlier," he told CNN.
Ebright is also not ready to discount the theory by the two Chinese researchers that the virus may have "leaked" from one of two labs near the Wuhan market, although one of the authors told The Wall Street Journal that they removed the article. because "it was not backed by direct evidence."
While Ebright said he did not believe the virus genome sequence showed "signatures of human tampering," he said there is a risk that a laboratory worker may have been accidentally infected.
CNN was unable to independently verify Ebright's arguments, and the study's lead author, Botao Xiao, did not respond to CNN emails and phone calls seeking comment.
Tensions between the United States and China slow down virus hunters
But one of the labs cited in the document, the Wuhan Virology Institute, issued a statement on February 19, firmly rejecting any suggestion that the virus originated at its facilities.
The statement says the theory that the virus leaked from the lab was one of the false rumors that "they did a lot of damage among our front-line researchers and seriously disrupted our urgent scientific research." Other rumors he rejected include that "the virus was created by man," "patient zero came from the institute," and "the Chinese military took control of the institute."
Chinese government officials say the source of the virus remains unknown and that others should stop "staining" the country.
"In fact, the source of covid-19 is a scientific problem," Luo Zhaohui, vice minister of foreign affairs, said in late March. "We need to hear professional and scientific opinions. The WHO has emphasized many times that linking viruses to specific races, skin colors, or geographic areas should be avoided. This is also the international consensus. "
Other researchers contacted by CNN were skeptical about the theory of laboratory accidents.
"I think he has no credibility," said Racaniello, who hosts a podcast called "This Week in Virology."
"I think it is part of human nature to think that we are doing the worst things, as opposed to nature."
Anthony, who had not heard of the article when contacted on Friday, said "it all sounds crazy."
"Laboratory accidents do happen, we know that, but ... there is certainly no evidence to support that theory," he said.
Meanwhile, tensions between the US USA and China on the origins of the virus, compounded by accusations of misinformation on both sides, are slowing down the work of virus hunters, who are punished by the same travel restrictions that have paralyzed the world.
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"If there was a so-called intermediate host, an animal that the bat virus got into and then allowed to get into people, the virus could still be in that host," said Daszak, the virus hunter working in China. "And there are hundreds, thousands of these animals and farms, and maybe the virus is still there. So even if we get rid of the outbreak, there is still a chance that that virus will re-emerge and we need to find it out quickly. ”
CNN's Jenny Friedland, Dan Logan and Zac Leja contributed to this report.
Genetics