Researchers confirm Covid-19 originated from livestock market in Wuhan

International research teams, led by the University’s virus evolution expert Michael Worobey, traced the start of the pandemic to the Wuhan market. Their findings were published this Tuesday in two papers in the journal ‘Science’.

Since then, peer-reviewed publications containing additional analysis and results are available virtually. Eliminate alternative scenarios put forward as the source of the pandemic. Furthermore, the authors concluded that the initial spread from animals to humans probably occurred in two separate transmission events in the Huanan market in late November 2019.

One of the studies examined the locations of the earliest known cases of Covid-19 and swab samples taken from surfaces in various marketplaces. The other focused on genomic sequences of SARS-CoV-2 from samples collected from Covid-19 patients during the first weeks of the pandemic in China.

The first study, conducted by Worobey and Kristian Andersen at the Scripps Research Institute in San Diego, California, Geographical structure of Covid-19 cases in the first month of the epidemicDecember 2019. The team was able to locate nearly all of the 174 Covid-19 cases identified by the World Health Organization that month, 155 of which were in Wuhan.

Analysis showed thatThese cases are clustered closely around the Huanan market., subsequent cases spread widely to Wuhan, a city of 11 million. In particular, the researchers found that a staggering percentage of early-stage Covid patients with no known connection to the market (meaning they did not work or shop there) live near the market.

“This supports the idea that the market is the epicenter of the epidemic.‘, says Worobey, explaining that the vendors were infected first, causing a chain of infections among surrounding community members.

“In a city that covers more than 5,000 square kilometers, the area most likely to contain the home of someone with one of the first cases of Covid-19 in the world was an area within a few streets of the Huanan market,” said Worobey, head of the Department of Ecology and Evolutionary Biology at the University of Arizona.

However, this result was supported by another finding. When the authors looked at the geographic distribution of Covid cases after January and February 2020, “opposite gun” patternIn Worobey’s words. December 2019 cases were drawn “like the bull’s eye” in the market, while subsequent cases coincided with the most densely populated areas in Wuhan.

“This tells us that the virus is not circulating in an encrypted form,” says the researcher. “It really originated in that market and spread from there,” he says.

Cases admitted to hospital

“It is important to be aware that all these cases were people diagnosed because they were hospitalized.“None of them was a mild case that could be detected by knocking on the door of those living near the market and asking if they were feeling bad,” the expert adds. In other words, these patients were enrolled “because they were in the hospital, not because of where they lived,” he said.

To eliminate any possibility of bias, Worobey’s team went a step further. Starting with the market, they started removing the cases from their analysis, moving further and further away from the market and re-running the statistics. The result was that the results were the same even when two-thirds of the cases were eliminated.

“Even in this scenario, with most cases eliminated, we found that: the rest lived closer to market than expected Worobey, if it weren’t for a geographic correlation between these early Covid cases and the market.

Positives about positions

The study also examined samples swabs from market surfaces such as floors and cages, after its closure. Samples that tested positive for SARS-CoV-2 were significantly associated with stalls selling live wildlife.

Researchers have identified Mammals now known to be susceptible to SARS-CoV-2, including red foxes, badgers and raccoon dogs, were being sold live on the Huanan market. In the weeks before the first recorded cases of Covid-19.

“Upstream events remain unclear, but our analysis of the available evidence strongly suggests that the pandemic resulted from the first human infections from animals sold at the Huanan Seafood Wholesale Market in late November 2019,” said Andersen, co-author of both studies. Said.

From animals to humans

The second study, an analysis of SARS-CoV-2 genomic data from the first cases, was co-led by Jonathan Pekar and Joel Wertheim of the University of California, San Diego, and Marc Suchard of the University of California, Los Angeles. , both in the United States and by Andersen and Worobey.

The initial pandemic Contained two different strains of SARS-CoV-2, possibly resulting from at least two separate human infections from animals In Huanan market in November 2019 and maybe in December 2019. The analyzes also show that the Covid-19 19.19 registered in the market during this period.

To establish a framework for the evolution of SARS-CoV-virus strains, the authors used a technique known as molecular clock analysis, which relies on the natural rate at which genetic mutations occur over time.

They found that the hypothesis of a single, rather than multiple, entry of the virus into humans would be inconsistent with the molecular clock data. Previous studies had suggested that a lineage of the virus, named A, closely related to viral relatives in bats, gave rise to a second lineage, called B.

Most likely, according to new data, it is a scenario. The two lineages both jumped from animals to humans on separate occasions in the Huanan market, according to Worobey.

Thus, the two studies provide evidence that Covid-19 emerged in the Huanan market after being transmitted from animals to humans, possibly from bats carrying the coronavirus in the wild or on farms in China.

Going forward, the researchers say scientists and government officials should work to better understand the wildlife trade in China and elsewhere and encourage more extensive testing on live animals sold in markets to reduce the risk of future pandemics.