A FRESH analysis of the earliest covid-19 cases has bolstered the argument that the pandemic began at the Huanan market in Wuhan, China.
A World Health Organization report on the origins of SARS-CoV-2, published earlier this year, states that the first person known to have covid-19 became ill on 8 December 2019 and had no connection to the market, which sold live animals.
However, this man – a 41-year-old accountant who was living 30 kilometres from the market – went to hospital on 8 December because of dental problems and only had covid-19 symptoms on 16 December, says Michael Worobey at the University of Arizona in his analysis.
These dates are confirmed by media interviews with the man, hospital records and a scientific paper. That means the earliest known cases were indeed linked to the market. The first was a seafood vendor who became ill on 11 December 2019 (Science, DOI: 10.1126/science.abm4454).
Why this isn't in the WHO report is unclear, as the team did speak to the accountant. “My guess is that they were told that this was the ’December 8’ patient and just accepted it as read,” says Worobey.
A WHO spokesperson says: “The team did meet with some early patients, but those were not epidemiological interviews collecting health data that would put them in the timeline. Those interviews were done by Chinese authorities in 2020.”
According to the WHO report, a third of 168 cases in December 2019 had links to the market. This is what one would expect if it was the source, says Worobey. The original SARS-CoV-2 virus was highly infectious and could spread asymptomatically, so many cases would lack a direct link to the source.
It has been suggested that this apparent link to the market is due to bias, as authorities began looking for cases linked to it once they were told of a possible connection on 29 December 2019. Worobey says this idea crumbles when you look at the three hospitals where doctors first realised something was up. They identified 19 unexplained pneumonia cases, of which 10 were linked to the market, before authorities were alerted. What's more, many early cases were linked to the western part of the market, which sold live animals such as raccoon dogs, a potential intermediate host for the virus to jump from bats to humans.
“Combined, this is compelling evidence that covid-19 has a live-animal-associated market origin, much like the first SARS virus,” says David Robertson at the University of Glasgow, UK. “Whether the initial transmissions were from animals to customers in the market, via vendors or both is hard to say.”
10 Pneumonia cases linked to Huanan market in late 2019
Not everyone agrees. “There is nothing new in this article which could make a natural origin of SARS-CoV-2 more likely than a laboratory one,” says Rossana Segreto at the University of Innsbruck in Austria.
But other recent findings have weakened the case for a lab origin, which some researchers say was never strong. In particular, coronaviruses that are the closest match yet found to SARS-CoV-2 have been discovered in bats in Laos. These wild viruses have features in common with SARS-CoV-2 that some had claimed could only have arisen in a lab during so-called gain-of-function experiments, showing these features can and do evolve in the wild.