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#Post#: 38--------------------------------------------------
Mysteries of covid19
DIR By: guest3
Date: June 25, 2021, 2:36 pm
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Following a month-long fact-finding mission in China, a World
Health Organization (WHO) team investigating the origins of the
COVID-19 pandemic concluded that the virus probably originated
in bats and passed to people through an intermediate animal. But
fundamental questions remain about when, where and how
SARS-CoV-2 first infected people.
As the international WHO team finalizes a report of its
findings, which is expected next week, Nature speaks to four of
the investigators about what they still want to know.
Was the virus circulating in Wuhan before the first known cases?
To trace the virus’s origin, it’s crucial to pin down exactly
when the first cases occurred in people. The WHO team
established that the first person known to have COVID-19 was an
office worker in Wuhan with no recent travel history, who began
showing symptoms on 8 December 2019, says Peter Ben Embarek, a
food-safety scientist at the WHO in Geneva, Switzerland, who led
the investigation. But the virus was probably spreading in the
city before that, because it was well-established by later that
month, he says.
Yet evidence of earlier spread has proved elusive. Researchers
in China conducted an extensive survey of patient reports from
hospitals in Wuhan made between October and December 2019, and
identified fewer than 100 people who had symptoms of COVID-19.
They then tested the blood of 67 of those people for antibodies
generated by past infection with SARS-CoV-2, but found none.
This suggests there wasn’t a large cluster of infections before
December, or an unusual spike in deaths in the surrounding
province of Hubei.
But Ben Embarek says the analysis should be repeated using less
restrictive symptom criteria, to make sure that researchers spot
all potential COVID-19 cases.
Scientists in China should also search for evidence of past
infection in some 200,000 archived samples currently held at the
Wuhan Blood Center and in other regions across China, says team
member Dominic Dwyer, a medical virologist at New South Wales
Health Pathology in Sydney, Australia. This would show whether
the virus was spreading in the general population in China — not
just among people who went to health facilities — before
December 2019.
Some scientists not involved in the WHO investigation have
already looked at blood-bank samples taken up to a year before
the pandemic, in Guangzhou, southern China. (Close relatives of
SARS-CoV-2 have been found in bats and pangolins in southern
China.) Some of the samples tested positive for antibodies
against SARS-CoV-2, but Ian Lipkin, an infectious-diseases
researcher at Columbia University in New York City, who worked
on the analysis, says the test was not specific enough to say
for sure that the antibodies weren’t caused by infection with
other viruses. “There is a lot of laboratory work that needs to
be done that hasn’t been done,” says Lipkin, who also wants to
know whether there are autopsy samples from before December 2019
that could be studied for traces of viral genetic material.
Was the virus spreading in people outside China before December
2019?
Answering this question is also key to establishing the timeline
of the first COVID-19 cases. Previously, researchers in Europe
have reported1,2,3 finding antibodies against SARS-CoV-2 in
samples taken at blood banks from November 2019 onwards.
Ben Embarek says this doesn’t necessarily suggest the virus
originated in Europe, but supports the idea that it was
spreading in Wuhan before the first known cases. “Wuhan at that
time was a very well-connected international city with direct
flights to the entire planet on a daily basis. So if it was
circulating in Wuhan, it could easily have been brought to other
parts of the world through travellers, and circulating again,
undetected, in different regions,” he says.
Still, he recommends that the blood samples from Europe be
retested to confirm that they indicate cases of COVID-19. Some
of them, from Italy and France, are already being reanalysed, he
says.
What was the role of the Huanan market?
The intermediate animal that passed the virus from bats to
people has not been identified, but researchers think it might
be a wild species that is sold as food in ‘wet markets’, which
typically sell live animals. Early in the pandemic,
investigators homed in on the Huanan Seafood Market in Wuhan,
because it sold fresh and frozen animals and many of the
earliest infections were in people who had visited it. But the
lead went cold when other early cases were found that were not
associated with the market. Viral material was identified in
drains and sewage at the market, but none was found on any
animal carcasses.
Still, the market is the only place where a large number of the
people infected at the start of the outbreak were exposed to
meat and animals. It’s important to establish how the virus got
into the market and whether it was on an animal, says WHO team
member Hung Nguyen-Viet, an environment and food-safety
researcher at the International Livestock Research Institute in
Nairobi.
Nguyen-Viet says the team identified ten stalls selling
wildlife, either wild or farmed, that could have carried the
virus into the market from farms in southern China. Some wild
animals sold for meat, such as rabbits and ferret-badgers, are
susceptible to SARS-CoV-2 or the related virus that causes
severe acute respiratory syndrome (SARS).
WHO team member Peter Daszak, president of the non-profit
research organization Ecohealth Alliance in New York City, says
the farms should be investigated to see whether there were
infections in the animals or among workers. He also wants to
know what animals were sold in other Wuhan markets. When the
team interviewed the first person known to have COVID-19, he
mentioned that his parents had visited a local community wet
market, says Daszak.
Did frozen wild-animal meat have a role in the early spread of
the virus?
The WHO team concluded that it’s most likely the virus jumped
from live animals to people, but Ben Embarek says it is possible
the virus entered the Huanan market through infected frozen wild
animals from farms in southern China, and then sparked an
outbreak. Daszak wonders whether frozen ferret-badgers sold at
the market could have carried the virus. “These were carcasses
skinned at the market, not just cubes of meat in a plastic
packet,” he says.
Can COVID spread from frozen wildlife?
Although researchers in China have also isolated viral RNA from
the packaging of imported frozen fish4, Ben Embarek says the WHO
team concluded that these goods were not likely to be the route
of the virus’s first arrival in Wuhan.
Lipkin says there is no evidence that the virus entered the
market through infected frozen wild animals. It could have just
as easily been brought in by infected people who handled wild
animals, he says.
Was the virus circulating in animals in China before the
pandemic?
To establish which animal passed the virus to people,
researchers need to find evidence of the virus in that species.
Researchers in China tested some 30,000 wild, farmed and
domestic animals in 2019 and 2020 but found no evidence of
active or past SARS-CoV-2 infection, except in some cats in
Wuhan in March 20205.
However, Ben Embarek says these surveys were not representative
of China’s overall animal population, and that many more animals
need to be tested for traces of infection, particularly on
wildlife farms. “The amount of testing that’s been done is not
sufficient to say, in any way, that wildlife farms were not
carrying the virus,” says Daszak.
The explosive way in which the outbreak took off in Wuhan in
December suggests that the virus was probably introduced once,
through the wildlife trade, says Daszak. He says future testing
should focus on farmed wild animals.
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