In October 2014, Virologist Edward Holmes took a tour of the Huanan Seafood Wholesale Market in Wuhan, a relatively overlooked city of about 11 million people in central China’s Hubei province. The market would have presented a bewildering environment to the uninitiated: rows of stalls selling unknown creatures for food, both dead and alive; cages containing hog badgers and Siberian weasels, Malaysian porcupines and masked palm civets. In the southwest corner of the market, Holmes found a stall selling raccoon dogs, stacked in a cage on top of another that housed a species of bird he didn’t recognize. He stopped to take a picture.
Eight years later, this photo is a key piece of evidence in the painstaking effort to trace the coronavirus pandemic back to its origins. Of course, it has been suspected since the early days of the pandemic, since it was even a pandemic before that, that the wet market in Wuhan played a role, but it has been difficult to prove definitively. Meanwhile, other origin theories have flourished centered on the Wuhan Institute of Virology, a biological research laboratory that is said to have accidentally or deliberately unleashed the virus on the city and the world.
The overwhelming scientific consensus is that Covid originated in a similar way to related diseases like SARS, which jumped from bats to humans via an intermediate animal. Figuring out exactly what happened with Covid-19 could prove immensely valuable both in terms of finally debunking the lab leak theory and in providing a source of information on how to stop the next pandemic. “It’s not about blaming,” says Kristian Andersen, a professor of immunology and microbiology at the Scripps Research Institute in California. “It’s about understanding the origins of the Covid-19 pandemic in as much detail as possible.”
For the past two years, an international team of scientists, including Andersen and Holmes, has been trying to pinpoint the epicenter of the pandemic, using methods ranging from genetic analysis to social media scraping. His research, which attracted extensive coverage in preprint before being published in its final form last week, reads as much like a detective report as an academic study.
First: the crime scene. Where exactly in this city of 11 million people did the virus first jump from animals to humans? To find out, the team, led by University of Arizona biologist Michael Worobey, looked to a report published by the World Health Organization in the summer of 2021, which was based on joint research that the public health body carried out with Chinese scientists. By crossing the various maps and tables in the report, the researchers obtained coordinates of 155 of the first cases of Covid in Wuhan, people who were hospitalized with the disease in December 2019.
Most of these cases were clustered around central Wuhan, especially on the west bank of the Yangtze River, the same area as the Huanan market. “There was this extraordinary pattern where the highest density of cases was very close and very concentrated in the market,” says Worobey, lead author of the paper, which was published in science. The statistical analysis confirmed that it was “extremely unlikely” that the pattern of cases seen in the early days of the pandemic would have been so clustered in the market if Covid had originated anywhere else – a random selection of similar people from Wuhan it was very unlikely. having lived so close to the market.