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A study published in Cell traces market wildlife to investigate COVID-19 origins.
Prof James Wood, Infectious Disease Epidemiologist at the University of Cambridge and Co-Director of Cambridge Infectious Diseases, University of Cambridge, said:
“The paper by Crits-Christoph and others is a high quality set of studies, representing a detailed analysis of a major public dataset, released earlier this year by Chinese workers. The conclusions in the paper are supported by these careful and through analyses and there is discussion of the limitations of the paper.
“The work provides very strong evidence for wildlife stalls in the Hunan Seafood Market in Wuhan being a hotspot for the emergence of the Covid-19 pandemic. The viruses that were detected in samples collected by Chinese workers from the market on or after 1st January 2020 showed the same range of viral variation in them that had been previously reported for the human cases sampled early in the course of the pandemic emergence; this variation was found to co-exist with the presence of DNA from wildlife species, such as Racoon Dogs. This evidence is entirely consistent with a wildlife market origin for the pandemic emergence. This evidence is carefully discussed by the authors. The limitation of the work is that market samples were not taken before the market closed around 1st January 2020 and the pandemic viruses are thought to have arisen 4-6 weeks before this date. The virus results are what one might expect to find had the pandemic originally arisen around a wildlife market stall or stalls – but they cannot provide direct evidence of this simply because of the sampling dates.
“The work is important because, as noted in the press release, while efforts have been made globally to tighten up on laboratory biosecurity to ensure that viruses cannot inadvertently escape (an alternative hypothesis for pandemic origins, which is not supported by the evidence here), little or nothing has been done to limit either the live trade in wildlife nor the biodiversity loss or land use changes that are the actual likely drivers of past and future pandemic emergence. These aspects are also not included in the draft pandemic treaty. Uncontrolled transmission of animal infections poses a major risk of future pandemics; this is a truly global issue, with a major outbreak of an avian derived influenza virus transmitting in a largely uncontrolled manner in North American dairy cattle throughout 2024.”
Prof Alice Hughes, Group Leader Biodiversity Analytics of Terrestrial Ecosystems (BAT) group, University of Hong Kong, said:
Does the press release accurately reflect the science?
“Largely yes, the only inaccuracy is that it states “Many of the key animal species had been cleared out before….” As far as we are aware all animals were removed before swabbing, and the closure of the market. If animals had still been present they would likely have been impounded and tested – however the science is all accurately reported in the press release.
Is this good quality research? Are the conclusions backed up by solid data?
“Yes they are. This is a good study which not only supports our earlier surmises, but also adds new information demonstrating the movement of animals (and their viruses) through the wildlife trade within China. Furthermore, the sequencing data of raccoon dogs highlights that animals are being bought into trade from the wild from South China, rather than being the typical captive farmed stock. With the other recent paper also highlighting the volume of viruses within fur farms in China this shows that the lack of regulation, the fact that wild animals are being bought into captivity (and without standards on biosafety) means there is a huge potential for the spillover and spread of novel zoonotic pathogens.
How does this work fit with the existing evidence?
“Whilst some former papers provided an implausible list of species which could not have been present (based on poor alignment probability and a biased reference dataset), this paper is in line with more rigorous papers on species in trade within the market, what we would expect to see within a market, and what had been seen and recorded in Huanan and other regional Chinese markets. The species present, and other data (such as where positive samples were collected) corroborates previous suppositions on the potential role of competent hosts as a potential origin of SARS-CoV2, and the role of the market as an initial source of viral spread. Furthermore, additional tests have been done, such as the potential existence of bats (which had been stated as potentially present in previous analysis) and this determined that the sequences identified were not sufficient to confirm bats were present. This is also to be expected, as whilst bats are consumed across Southeast Asia and South China, with the exception of fruitbats (which had not been indicated in prior analysis) smaller insectivorous bats are rarely sold in an open market environment such as this, and are more commonly traded among individuals by links to hunters.
Have the authors accounted for confounders? Are there important limitations to be aware of?
“They have as much as is possible. Without swabs from the actual animals in the market (which were not collected) we cannot obtain any higher certainty in the animals being infected, but the high concentrations of positive swabs in the areas of the market where animals were housed does support the probability of a link between wildlife and infection.
What are the implications in the real world? Is there any overspeculation?
“No, this is a field where authors know that outputs will be scrutinised and so analysis must be careful. The paper lends extra support to the potential role of Huanan in the early stages of the pandemic, demonstrates the movement of animals, including wildlife across China for trade and consumption. It also shows that wild animals are still being caught, and sold, even in large cities, and calls for tighter regulation and monitoring of the trade of all wild species in China, as well as the clear need for better biosafety if we are to reduce the risks of future spillover of zoonoses with epidemic, or pandemic potential. It is also a reminder of the importance of sharing data, as this analysis would not have been possible without the sharing of the swab data collected from the market at the outset of the pandemic.”
‘Genetic tracing of market wildlife and viruses at the epicenter of the COVID-19 pandemic’ by Alexander Crits-Christoph et al. was published in Cell at 16:00 UK time on Thursday 19 September 2024.
DOI: 10.1016/j.cell.2024.08.010
Declared interests
Prof James Wood: “My interest statement is that I am funded by or have received funding from a mixture of bodies over the last 5 years, including The Wellcome Trust, UKRI, The Bill and Melinda Gates Foundation, FCDO / DfID, Defra, The Alborada Trust and Horizon 2020. Among other topics, I have conducted collaborative studies of zoonotic virus infections in bats and livestock in Africa, particularly Ghana. I have been on advisory committees for Defra, APHA, Roslin Institute and the Noguchi Memorial Institute for Medical Research. I am employed by the University of Cambridge.”
Prof Alice Hughes: “I have no conflict of interests.”