China’s wildlife trade should be thoroughly investigated as part of efforts to uncover the origin of the coronavirus pandemic, say researchers. The call comes as the World Health Organization (WHO) is sending scientists to China this weekend, ahead of plans for a larger international research team to probe the pandemic’s origin.
“The mission objective is to advance the understanding of animal hosts for COVID-19 and ascertain how the disease jumped between animals and humans,” said Tedros Adhanom Ghebreyesus, the WHO’s director-general, at a press briefing on 7 July.
The team will work closely with officials and the scientific community in China to decide what kind of investigations are needed and where, said Michael Ryan, director of the WHO’s emergencies programme. He said a good place to start is in Wuhan, where the first clusters of atypical pneumonia emerged.
Researchers say the focus should be on activities linked to China’s wildlife trade — both legal and illegal — including hunting areas, storage facilities, farms and markets. “All parts of the wildlife supply chain need to be investigated,” says Alice Latinne, an evolutionary biologist at the Wildlife Conservation Society Vietnam in Hanoi. “We need to test any wild or farmed wild animal species that could potentially be in close and frequent contact with humans in China,” she says.
Most researchers agree that the SARS-CoV-2 virus probably originated in horseshoe bats, but the route it took to get to humans remains a mystery. The virus could have jumped directly from bats to people and evolved over time into the current pandemic strain, or it could have passed through intermediate animals.
Researchers say that the wildlife trade — in which many animals come into close proximity with each other and people — offers the perfect conditions for a virus in one species to spill over into another.
Early in the pandemic, pangolins were thought to be a possible intermediate host of the SARS-CoV-2 virus when researchers detected related coronaviruses in animals that had been seized in southern China between 2017 and 2019. Pangolins are found across southeast Asia and are among the most trafficked animals in the world for their scales, which are used in traditional Chinese medicine. The coronaviruses found in the pangolins were too different to be SARS-CoV-2’s direct ancestor, but researchers say that when and how the animals got infected could provide clues about where SARS-CoV-2 originated.
A preprint1 posted on bioRxiv on 19 June suggests that pangolins probably catch the viruses during the process of being traded. The study looked at more than 300 pangolins in Malaysia, which the authorities seized or locals rescued while en route to China between 2009 and 2019, and found no coronaviruses.
The evidence suggests that the pangolins seized in China were exposed to coronaviruses while being transported to their final destination, rather than in the wild, says Jimmy Lee, a researcher with the non-profit EcoHealth Alliance Malaysia in Kuala Lumpur and the paper’s first author. “Pangolins are most likely incidental hosts infected within the wildlife trade,” says Lee, but more research is needed to rule them out as an intermediate host of SARS-CoV-2.
The pangolins could have been infected by other traded animals or the people that smuggled them, says Yujia Alina Chan, a geneticist at the Broad Institute of MIT and Harvard in Cambridge, Massachusetts. In raids, smuggled pangolins have been found with masked palm civets, an intermediate host of the virus that causes severe acute respiratory syndrome, and with bat carcasses.
The investigators should scrutinize the circumstances in which the pangolins in China were seized, the animal species they were housed with, and whether people involved in the wildlife trade have coronavirus antibodies, says Arinjay Banerjee, a coronavirus researcher at McMaster University in Hamilton, Canada. Following that trail could help scientists find a closer relative to SARS-CoV-2, he says.
The WHO investigations should also look at other mammals commonly hunted and traded in southern China, especially small carnivores and rodents, says Latinne. Another priority should be bats in the southern province of Yunnan, she says — a hotspot for bat coronaviruses where the closest known relative to SARS-CoV-2, called RaTG13, has been identified2.
But the investigations should not be limited to China, says Alice Hughes, a conservation biologist at the China Biodiversity Conservation and Green Development Foundation in Yunnan. Many species move across borders, and people in neighbouring countries are also in frequent contact with wild animals. Significant harvesting of bat excrement, or guano, occurs under unhygienic conditions in countries such as Laos, Thailand and Cambodia, and many of these do not have the capacity to clamp down on the wildlife trade, says Hughes.
Researchers should also keep an open mind, and look beyond the wildlife trade and known coronavirus reservoirs, says Sophie Gryseels, an evolutionary biologist at the Catholic University of Leuven, Belgium.
The origin of the pandemic has become a highly sensitive topic in China, and researchers need government approval to publish their research. Scientists in the country say that some animals, including bats and livestock, have been tested for SARS-CoV-2, but no results have been published. The WHO mission could reveal more information about these investigations, and build trust between the international community and researchers in China.
“It will be the first unbiased effort to communicate with Chinese scientists and public-health leaders on this very sensitive and politicized issue,” says Peter Daszak, the president of EcoHealth Alliance in New York City.
A diverse group of experts from a range of countries and disciplines could also provide fresh insights to Chinese researchers who are probing the coronavirus’s origin, says Dale Fisher, an infectious-disease researcher at the National University of Singapore.
But researchers should also be prepared to find nothing, notes Gryseels, who says the search will be “looking for a needle in a haystack the size of Asia or larger”.
Nature 583, 344 (2020)