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WHO team rejects lab origin of coronavirus, focuses on animals, frozen food:

After 12 days of field work in Wuhan, China, an international team of scientists assembled by the World Health Organization have wrapped up its investigation into the origins of the SARS-CoV-2 virus that mushroomed out of the city in December of 2019.

The team's findings support researchers' previous leading hypothesis of how the pandemic began—that the virus used a still-elusive intermediate animal host as a bridge to infect humans from a distant reservoir host, such as horseshoe bats. But the team did fill in new, intriguing details of the pandemic's first, crucial month—and ruled out sensational theories that the pandemic was born from a laboratory incident.

"Our initial findings suggest that the introduction [to humans] through an intermediary host species is the most likely pathway," Peter Ben Embarek, WHO International Team Lead, said in a 3-hour press conference on the team's findings, livestreamed from Wuhan on February 9. Though researchers in China have already surveyed 11,000 animals around the country in search of that host, all have tested negative for SARS-CoV-2 so far, the team noted. Identifying the intermediary host "will require more studies and more specific, targeted research," Embarek added.

[...] In all, the investigators settled on exploring four main hypotheses:

1. The intermediary host hypothesis, which they found most likely
2. The lab origin hypothesis, which they ruled out
3. A direct zoonotic spillover hypothesis, which they also determined is unlikely
4. And an indirect transmission from frozen food or through the cold supply chain, which they left open

Hypothesis 3 would require direct transmission to a human from an infected reservoir animal, such as horseshoe bats or perhaps a pangolin. Both animals have been found carrying viruses genetically related to SARS-CoV-2, and horseshoe bats are well-known for carrying diverse populations of coronaviruses. But, given that Wuhan lacks bat populations, the researchers deemed it unlikely that a direct transmission from such an animal as a bat was the spark that set off the roaring pandemic.

Instead, they think it more likely that the virus jumped to an intermediate animal species that had more regular contact with humans, giving the virus plenty of opportunities to evolve to infect humans and then spread among them. This is how other infamous coronaviruses—including SARS-CoV, the cause of SARS—spread to people. Since SARS-CoV-2 emerged, it's become clear that it several animal species are highly susceptible to the virus, including mink and cats.

"Generally speaking, a virus causing a global pandemic must be highly adapted to human environments," Dr. Liang Wannian, Chinese team lead and executive vice dean of school of public health at Tsinghua, said in today's press conference via an interpreter. "Such adaptations may occur suddenly or may have evolved through multiple steps, with each step driven by natural selection."

The WHO team is now keenly interested in further studies looking into the animals and animal products that are commonly moved into and out of Wuhan—including frozen ones.

Also at CNET, CNN

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