[In a review of recent studies and comparisons to other outbreaks, a group of virologists contends that there is more evidence to support a natural spillover from animals to humans.]
By Carl Zimmer and James Gorman
Among other things, the scientists
point to a recent report showing that markets in Wuhan, China, had sold
live animals susceptible to the virus, including palm civets and raccoon
dogs, in the two years before the pandemic began. They observed the striking
similarity that Covid-19’s emergence had to other viral diseases that arose
through natural spillovers, and pointed to a variety of newly discovered
viruses in animals that are closely related to the one that caused the new
pandemic.
The back and forth among scientists
is taking place while intelligence agencies are working with an
end-of-summer deadline to provide President Biden with an assessment
of the origin of the pandemic. There is now a division among
intelligence officials as to which scenario for viral origin is more likely.
The new paper, which was
posted online on Wednesday but has yet to be published in a scientific
journal, was written by a team of 21 virologists. Four of them also collaborated
on a 2020 paper in Nature Medicine that largely dismissed
the possibility that the virus became a human pathogen through laboratory
manipulation.
In the new paper, the scientists
provided more evidence in favor of the virus having spilled over from an animal
host outside of a laboratory. Joel Wertheim, a virologist at the University of
California, San Diego, and a co-author, said that an important point in support
of a natural origin was the “uncanny similarity” between the Covid and SARS
pandemics. Both viruses emerged in
China in the late fall, he said, with the first known cases popping up near
animal markets in cities — Wuhan in the case of Covid, and Shenzen in
the case of SARS.
In the SARS epidemic, the new paper
points out scientists eventually traced the origin to viruses that infected
bats far from Shenzen.
Based on the distribution of
viruses similar to the new coronavirus across Asia, Dr. Wertheim and his
colleagues predict the origin of SARS-CoV-2 will also be far from Wuhan.
Since first surfacing in the final
months of 2019, this pandemic’s viral culprit has yet to be found naturally
occurring in any animal.
In May, another team of 18
scientists published a letter arguing that the possibility of a lab
leak needed to be taken seriously, because there was too little evidence to
favor a natural origin of the coronavirus or a leak from a lab. Wuhan, where
the pandemic was first documented, is home to the Wuhan Institute of Virology,
or W.I.V. for short, where researchers have studied coronaviruses from bats for
years.
One of the signers of the May 2021
letter, Michael Worobey of the University of Arizona, became a co-author of the
new paper arguing for a natural spillover.
He said his views have evolved as
more information emerges. Among other reasons for Dr. Worobey’s shift was the
growing evidence about the Huanan animal market in Wuhan. When the pandemic
first arose in Wuhan, Chinese officials tested hundreds of samples from animals
sold at the market and did not find the coronavirus in any of them.
But last month a team of
researchers presented an inventory of 47,381 animals from 38 species sold in
Wuhan markets between May 2017 and November 2019. It included species like
civets and raccoon dogs that can act as intermediate hosts for coronaviruses.
Dr. Worobey called that study “a
game-changing paper.”
He also pointed to the timing of
the earliest cases of Covid in Wuhan. “The Huanan market is right at the
epicenter of the outbreak, with later cases then radiating outward in space
from there,” Dr. Worobey said in an email.
“No early cases cluster anywhere
near the W.I.V., which has been the focus of most speculation about a possible
lab escape,” he said.
Other scientists, however, say that
such arguments are speculative, and that the new review is mostly a rehash of
what was already known.
“Basically, it really boils down to
an argument that because nearly all previous pandemics were of natural origin,
this one must be as well,” said David Relman, a microbiologist at Stanford
University who organized the May letter to Science.
He noted that he does not object to
the natural origin hypothesis as a plausible explanation for the pandemic
origin. But Dr. Relman thinks the new paper presented “a selective sampling of
findings to argue one side.”
Dr. Worobey and his colleagues also
presented evidence in their new paper against the idea that so-called gain-of-function
research that intentionally alters the function of a virus might have
played a role in the pandemic. The researchers argue that the genome of the
coronavirus shows no compelling signatures of being manipulated. And the
diversity of coronavirus scientists have been discovering in Asian bats could
have served as the evolutionary wellspring for Covid-19.
But Richard Ebright, a molecular
biologist at Rutgers University and a persistent critic of attempts to diminish
the likelihood of a laboratory leak, said that this was a straw-man argument.
Dr. Ebright said it was possible
that a W.I.V. lab worker might have contracted the coronavirus on a field
expedition to study bats or while processing a virus at the lab. The new paper,
he argued, failed to address such possibilities.
“The review does not advance the
discussion,” Dr. Ebright said.
Carl Zimmer writes the “Matter” column. He is
the author of fourteen books, including “Life's Edge: The Search For What It
Means To Be Alive.” @carlzimmer • Facebook
James Gorman is a science writer at
large and the author of books on hypochondria, penguins, dinosaurs and the
ocean around Antarctica. He writes about animals, viruses, archaeology and the
evolution of dogs.
