In the hunt for the source of the Covid-19 disease, the World Health Organization confirmed China identified supply chains for animals sold in Wuhan, where the first known outbreak occurred, a move based on the view the virus may have first infected traded wildlife. But identifying the supply networks is the first step, the next is to run comprehensive, targeted tests of animals and people involved to try and trace the path of the virus before the outbreak more than 12 months ago. To the puzzlement of some overseas experts, China’s authorities seemingly failed to follow up with this testing in supply routes leading back to farms and animal breeders in certain regions of the country. While an official report from a 28-day fact-finding mission to Wuhan led by the WHO has yet to be released , team members in official comments and media reports have said such testing was the “next step” in the investigation. “Some of the trace-back was in farms or in traders in regions that are known to harbour bats with the closest related viruses [to the one that causes Covid-19],” virologist Marion Koopmans said in Wuhan at the close of the WHO mission on February 9. “So it is really seen as an entry point … for taking the next step of surveys in animals on farms.” Another team member, disease ecologist Peter Daszak, said in an interview with CNN that scientists had not gone to farms of interest in southern China. “No one has been there to test the animals,” Daszak said in the interview, adding this research was agreed on as a “priority” by both the international WHO team and the Chinese scientists. Implausible? Other experts, who are not part of the mission, expressed surprise that Chinese authorities had not already done this targeted testing, as described in the CNN report. The consensus view among scientists is the virus may have come from bats, which are known to host similar coronaviruses, before infecting another animal and in turn humans. “I was a bit surprised that this work that you would expect to be done hasn’t been done, [especially as] China has some of the best scientists and epidemiologists,” said Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations in New York. Cambodian scientists find close match for pathogen in samples collected in 2010 He pointed to the government’s extensive work to trace the start of more recent Covid-19 outbreaks in the capital Beijing and Shijiazhuang in Hebei province. “There’s been all this commitment, this energy expended in tracing the origins [of those outbreaks] and you wonder why similar energy, similar commitment has not been used on tracing the origins of the pandemic,” he said. Infectious disease specialist Daniel Lucey of Georgetown University in Washington said it was “frankly implausible” that such testing had not been done. “My question is why would it not have been done? It was known to be necessary and it’s in China’s scientific interest, it’s in their public health interest and it’s in their national security interest,” he said. Ferrets, badgers and minks Other scientists say that targeted testing would be a typical feature of an outbreak investigation with a profile like that of Wuhan’s, where a number of early cases were linked to a market known to sell wild animals. In China, prior to the outbreak, breeding of certain wild animals on farms for food was legal. “Live animals in the market that are known to be susceptible to Sars-CoV-2 would be the first place you would look honestly,” said evolutionary biologist Eddie Holmes, referring as well to the supply chain. “They absolutely need to do that.” In particular, farms raising mammals from a family that includes ferrets, badgers and minks – animals known to be vulnerable to the novel coronavirus or its predecessor the Sars virus – would be “an obvious place” to run further testing, according to Holmes, a professor at the University of Sydney in Australia and a leading authority on the genetic evolution of the virus. China has run what WHO official and international team leader Peter Ben Embarek described as “a large amount of animal testing” of both livestock and wild animals throughout China, though said they returned no positives. This included testing tens of thousands of animals across the country for active infection from 2019 to 2020, according to Liang Wannian of the National Health Commission. In Wuhan, Hubei and neighbouring provinces, 50,000 samples from 300 species of wild animals before and after the outbreak were also tested for active infection, he said. Little picture While it is difficult to analyse this without a full breakdown of the information gathered, Wanda Markotter, director of the Centre for Viral Zoonoses, at South Africa’s University of Pretoria, said such a strategy alone could be too broad. “In a case like this, I would go for a more targeted approach, if you have the info,” she said, pointing to comprehensive testing on farms that supplied the market, as well as those where wild animals known to be able to catch the virus are bred as part of China’s regulated wildlife trade. Georgetown’s Lucey said “big picture” testing across species and locations could be useful, but should be paired with the focused testing along the market supply chain. Experts say it is best if such work is done as early as possible after an outbreak, but it is not too late to investigate and monitor animals on these farms for traces of past infection or new infections over time. However, questions remain about challenges to this research following China’s ban on breeding wildlife for food in February last year, which resulted in farm closures. A joint WHO-China report from that same month last year noted work was “already under way” in China to collect detailed records on the source and type of wildlife species sold at the market. The National Health Commission did not respond to a request for comment on animal testing in southern China by publication time. Transparency Few details about China’s investigations into the origins of the virus have been made publicly available prior to the WHO mission, even as the virus spread around the world. The US has raised concerns about China’s transparency around the start of the outbreak and cooperation with the mission. Chinese officials have repeatedly suggested that the virus may have emerged elsewhere and origins tracing will also need to take place in other countries. China’s Covid-19 origin theory includes pig heads and frozen fish An internal WHO document has cast doubt on the level of work that Chinese scientists had done to uncover the origins of the outbreak, The Guardian reported on Tuesday. The brief, written in August following a trip by two WHO experts to China to plan the recent mission, said “it appears that little had been done in terms of epidemiological investigations around Wuhan since January 2020”, according to the newspaper, which said it had seen the document. China has defended its record and said it has “kept close communication and cooperation with the World Health Organization on global origin-tracing in an open and transparent spirit”.