Scientist Looks Anew at Raccoon Dog Data, Stressing the Unknowns

A brand new research of genetic knowledge from a market in Wuhan, China, mentioned the info didn’t help the case that the pandemic had began with illegally traded animals, touching off recent debate about samples that different scientists see as crucial items of the puzzle of how the coronavirus reached people.

The new research, which examined the relative quantities of animal and viral materials in swabs taken from surfaces on the market in early 2020, mentioned it was tough to attract conclusions about whether or not given samples of the virus had come from contaminated reside animals or have been merely from incidental contamination.

But a number of outdoors consultants mentioned the evaluation, posted on-line this week by the research’s creator, Jesse Bloom, a virologist on the Fred Hutchinson Cancer Center, might have been affected by a lot of unknown variables and selections about methods to filter the info.

For these causes, they mentioned, the findings didn’t do a lot to sway their impression of earlier research. Samples from the market containing animal and viral genetic materials, they mentioned, have been in step with the chance that an animal there — maybe a raccoon canine — had unfold the virus to individuals, however didn’t show that had occurred.

“I think there’s a pretty reasonable chance they picked up an infected raccoon dog, but that doesn’t prove that was the origin,” mentioned Frederic Bushman, a microbiologist on the University of Pennsylvania who focuses on analyzing samples like these taken from the Wuhan market, however who was not concerned in any of the market research. “I don’t think the Bloom paper changes my thinking that much.”

Chinese researchers wrote in regards to the market knowledge final yr after which made the genetic sequences accessible this yr, permitting a crew of worldwide scientists to check them. That crew wrote in a report final month that primarily based on the info, they might not conclusively establish an animal that had handed the virus to individuals.

But they mentioned the info confirmed that animals believed to be inclined to the virus, like raccoon canines and masked palm civets, a small Asian mammal implicated within the SARS outbreak twenty years in the past, have been being offered on the market in late 2019. Many of the earliest Covid-19 sufferers additionally labored or shopped on the market.

Because the market was certainly one of solely 4 locations in Wuhan reported to be promoting reside animals of the kind that might plausibly unfold the virus, the scientists mentioned it was unlikely that so many early sufferers have been linked to the market purely by probability. They mentioned the genetic knowledge additionally constructed on different proof, together with that two early lineages of the virus had been on the market.

This week’s research took a unique strategy to analyzing the gene sequences.

Dr. Bloom investigated whether or not the quantity of genetic materials from the virus correlated with the quantity of genetic materials from inclined animal species within the samples. If one species on the market was overwhelmingly answerable for shedding the virus, he mentioned in an interview, he would have anticipated to see a transparent hyperlink between the quantity of genetic materials from the virus and the quantity from that species.

But the research discovered no clear correlations of that sort. Instead, the strongest correlations concerned varied fish offered on the market that might not have been contaminated, a sign that contaminated individuals had in all probability deposited viral materials the place the fish was.

Dr. Bloom mentioned that discovering advised that the virus, also called SARS-CoV-2, was unfold broadly throughout the market by the point the swabs have been collected in early 2020.

“In the same way we shouldn’t read much of anything into the fact that there’s a bunch of SARS-CoV-2 mixed with largemouth bass and catfish samples, we also shouldn’t read much into the fact that there’s a raccoon dog sample with a SARS-CoV-2 read,” Dr. Bloom mentioned.

But outdoors consultants mentioned that varied options of the samples might throw off efforts to correlate animal and viral materials. The worldwide scientists mentioned of their report that that they had thought of operating an identical evaluation, however that it risked producing deceptive outcomes. Dr. Bloom acknowledged that “it’s an open question of whether that is an informative thing to calculate at all.”

Genetic materials from the virus degrades rapidly, mentioned Christopher Mason, a specialist in environmental sampling at Weill Cornell Medicine. Crucially, viral materials could decay at a unique fee than materials from animals, making it tough to check them in samples collected over the course of weeks after the market’s closure.

It might be that fish have been most intently related to the virus just because the fish have been prone to have been frozen or refrigerated, slowing the decay of viral materials in these samples, mentioned Tom Wenseleers, an evolutionary biologist at KU Leuven in Belgium.

The newest evaluation “confirms that looking at these sorts of correlations tells you next to nothing with respect to which host species could have been a plausible source of the pandemic,” Dr. Wenseleers mentioned. This leaves scientists in the identical scenario as earlier than, he mentioned, with market knowledge that doesn’t supply conclusive proof of any explicit origin situation.

The new research additionally appeared intently at a swab from a cart on the market by which the worldwide crew had discovered a hint of the virus alongside genetic signatures of raccoon canines, however no detectable genetic materials from people.

Dr. Bloom wrote that the swab had solely a minuscule quantity of viral materials, and that it was not clear why Chinese researchers had categorised the swab as Covid-positive. His research mentioned that swab was the one one which had substantial quantities of raccoon canine genetic materials with any traces of the virus.

Some scientists, although, mentioned Dr. Bloom’s evaluation risked dismissing different Covid-positive swabs by setting too excessive of a bar for the quantity of animal genetic materials in a pattern.

Dr. Bushman, of the University of Pennsylvania, mentioned that the brink used within the evaluation was “aggressive” and that it was greatest to check outcomes obtained from a collection of various cutoffs.

Using a extra delicate threshold, the worldwide crew of scientists recognized a number of Covid-positive samples containing raccoon canine genetic materials, in addition to others with genetic signatures of various animals regarded as inclined to the virus.

Alexander Crits-Christoph, a computational biologist previously at Johns Hopkins University who helped lead the worldwide crew’s evaluation, mentioned the crew additionally appeared intently at whether or not the Chinese researchers had been proper to explain the swab from the cart as constructive for the virus.

He famous that a lot of different swabs from the identical stall have been clearly constructive for the virus. He mentioned outcomes from sampling elsewhere out there additionally indicated that in contrast to the swab from the cart, many of the really damaging swabs contained no traces of the virus in any respect.

“This is environmental sampling of a virus that is a tiny needle in a haystack,” Dr. Crits-Christoph mentioned.