China probe: SARS-CoV-2 jump from go-between host most likely scenario

Chinese meat stall in outdoor market
Chinese meat stall in outdoor market

Noa / iStock

Representatives from China and an international joint mission team led by the World Health Organization (WHO) today in Wuhan detailed the results of a 2-week probe into the zoonotic source of the outbreaks, which didn't reveal a definitive source but did shed new light on the events.

At the nearly 3-hour briefing, officials laid out four main theories, some of them less likely possibilities. The 10-person joint mission team has been in China since Jan 14 and followed investigation terms that a WHO advance team fleshed out with the country over the summer.

The team was quarantined for the first part of its stay, followed by 12 days of field work that took them to locations in Wuhan, such as hospitals, the seafood market initially thought to have triggered the first outbreaks, and the Wuhan Institute of Virology (WIV).

Intermediary host most likely pathway

At the briefing, Peter Ben Embarek, PhD, who led the WHO team, said introduction through an intermediary host species is the most likely of the four scenarios, according to CNN. Confirmation will require more studies and targeted research.

Ben Embarek also said transmission through the sale of frozen products is possible. China has pushed the cold-chain packaging theory and has said the virus on imported frozen foods has been one likely source of small flare-ups that followed the country's first surge. However, over the past months, the WHO has said there's no evidence that people can contract the virus from food or food packaging.

The group's seafood market tour found that vendors were selling frozen animal products, including farmed wild animals, and further studies into the supply chain might be useful, he said, according to Reuters. "The possible path from whatever original animal species all the way through to the Huanan market could have taken a very long and convoluted path involving also movements across borders," Ben Embarek said.

The two other possibilities, a direct spillover from the animal reservoir and a lab-incident possibility, are less likely, Ben Embarek said. The spillover is still considered a topic of further study, though, while investigators assessed the lab-incident possibility as the least likely cause of SARS-CoV-2 jump to humans due to safety protocols that are in place at the facility.

Ben Embarek said the team was able to question lab scientists and administrators about coronavirus work that was done at the lab.

Some cases predated seafood market cluster

Liang Wannian, PhD, China's team lead, said the Wuhan seafood market that first emerged as the potential source of the outbreak may not have been the first place where the virus transmitted. He said the earliest illness onset for a confirmed COVID-19 patient was Dec 8, 2019, and that the earliest illness onset linked to the market was Dec 12.

Ben Embarek said a detailed case database review found no indications that there were large COVID-19 outbreaks before December 2019 in Wuhan or anywhere else in China, according to Reuters.

At the briefing, Chinese officials repeated their earlier assertions that the virus could have come from outside of China, and Liang said investigations going forward should not be restricted to any locations, according to the New York Times. Though a number of scientists dispute the possibility, the WHO team said they would weigh reports of early COVID-19 cases that occurred outside of China.

More studies needed in market animals

Investigators also urged more studies of the animals sold at the seafood market in Wuhan linked to the first reported patient cluster. Peter Daszak, PhD, a team member from the United States who is with EcoHealth Alliance, said on Twitter today that there were no SARS-CoV-2 positives from animals at the seafood market, but some are thought to be susceptible to coronaviruses, including ferret badgers.

Some also trace back to farms or regions where bats harbor coronaviruses. "This, to me, is a critical finding."

He also said the team recommends sampling intermediate hosts and bats in and outside of China, keeping in mind a possible role of frozen wild animals that could have been infected with SARS-CoV-2.

Liang said no labs in Wuhan worked with SARS-CoV-2, though the WIV researches coronaviruses from bats in southwestern China, including two known relatives of SARS-CoV-2, according to the Washington Post.

The WHO said today that the team will finalize a summary of the report in the coming days and that it will publish a link to the full findings, once the report is published.

High death count in Russia

Yesterday, new totals from Russia's statistics agency suggest that the country's COVID-19 deaths are much higher than previously reported, according to CNN. Earlier, the country had reported 57,555 COVID-19 deaths for 2020, but the latest number at 162,429 is sharply higher.

The latest number combines deaths directly related to the virus with those in which infection was a contributing factor.

The higher number would make Russia the third-highest country in cumulative deaths.

In other global headlines:

  • Tokyo's Olympic committee has released its COVID-19 playbook for the postponed Summer Games, which includes a plan for testing athletes and officials every 4 days, according to CNN.

  • Myanmar's COVID-19 testing has collapsed in the wake of the country's coup, according to Reuters.

  • The global total today reached 106,732,062 cases, and 2,333,776 people have died from their infections, according to the Johns Hopkins online dashboard.

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