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 The following looks at their findings.
WHAT ARE THE MAIN SCENARIOS?
Peter Ben Embarek, the WHO's leading animal disease expert, said the
team conducted scientific investigations into four main scenarios
about how SARS-CoV-2, the virus that causes COVID-19, spread into
humans.
In the first, a single person was exposed to SARS-CoV-2 through
direct contact with the host species, the horseshoe bat. The virus
could have been circulating in humans for a while before making its
breakthrough in heavily populated Wuhan.
The second scenario, seen as the most likely, involves transmission
to humans via an as yet unknown intermediary species. Liang Wannian,
an expert with China's National Health Commission, said pangolins
were potential candidates but other animals - including mink and
even cats - may also be reservoirs.
A third possibility is that COVID-19 originated under the first or
second scenarios and was then transmitted via cold chain products.
Chinese experts have attributed later COVID-19 clusters to imported
frozen food and have raised the possibility it might also have
caused the Wuhan outbreak.
The final scenario is that SARS-CoV-2 was leaked from the Wuhan
Institute of Virology, which is known to have studied captive
coronaviruses. Ben Embarek ruled out the possibility and said it
would not be subject to further research. Accidents happen, he said,
but it was "very unlikely" in this case.
WHEN DID THE OUTBREAK BEGIN?
The experts said that while it was unlikely there were large-scale
outbreaks in Wuhan or elsewhere in China before December 2019, they
do not rule out that it was circulating in other regions.
A crossover either directly from bats or from an intermediary
species would suggest the transmission to Wuhan could have been
facilitated by wildlife trading networks.
Marion Koopmans, another member of the expert team, said wildlife on
sale in the Huanan seafood market could be traced to regions that
contain bat habitats known to harbour viruses closely related to
SARS-CoV-2.
One such region is the southwestern Chinese province of Yunnan, but
the team is also considering that the first human transmission took
place across the border in Laos or Vietnam.
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WHAT ROLE WAS PLAYED BY HUANAN MARKET?
Although the Huanan seafood market in Wuhan was linked to the first
case clusters, the initial crossover from animals to humans did not
occur there.
Liang said that there was still insufficient evidence to determine
how the virus entered Huanan, but that it was clear it was
circulating elsewhere in Wuhan at the same time.
The most likely scenario is that someone carried SARS-CoV-2 into the
market, but Ben Embarek also suggested it could have been introduced
via a "product", including frozen wild animals known to be
susceptible to the virus.
DO THE FINDINGS CHANGE THE POLITICS AROUND COVID'S ORIGINS?
China has expressed concern that any investigation would be "politicised",
and said it would only cooperate if it was clear it would not be
expected to take blame for the pandemic.
By ruling out the lab leak and accepting that COVID-19 could have
originated outside of China, the WHO team has not crossed any of
Beijing's lines. China would also be heartened that the WHO team is
considering the cold-chain theory. But the findings are unlikely to
satisfy those who believe China is culpable and has covered up
evidence.
WHAT FURTHER RESEARCH IS REQUIRED?
Ben Embarek said China needs now to find evidence that might prove
the coronavirus was circulating much earlier than December 2019. He
said blood bank samples would be a good place to start.
Bat communities near Wuhan have been ruled out as a source, and more
needs to be done to scour caves in other regions to see if a closer
match to SARS-CoV-2 can be found.
The animals on sale at the Huanan market also need to be scrutinised
further, and the role played by cold chain products in general also
needs more research, Ben Embarek said.
(Reporting by David Stanway. Editing by Gerry Doyle)
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