The reporting was supported by a grant from the Pulitzer Center.
In the bustling Jatinegara market in Jakarta, cages are stacked three metres high, holding creatures from all corners of Indonesia and beyond. Bats, raccoon dogs, macaques and songbirds — sold as pets or food — are crammed together, their musky odours mingling with the stench of urine and faeces in the damp tropical air.
For decades, public-health experts have warned about the risks of infectious diseases jumping from animals to humans in markets such as Jatinegara, which are part of a global industry worth hundreds of billions of dollars annually. These markets remain “the best way of transmitting diseases”, says James Wood, a veterinary epidemiologist at the University of Cambridge, UK. Jatinegara’s location, in an international travel hub with a population of 11 million people, increases that risk considerably.
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The world is still recovering from the COVID-19 pandemic, which many researchers say probably started, or was at least amplified, at a market selling live animals in Wuhan, China1,2. Yet the wildlife trade still thrives in many parts of the globe. China banned the farming and trading of most wildlife species for food in 2020, but these practices have simply gone underground. “We are back to business as usual,” says Vincent Nijman, a conservation biologist at Oxford Brookes University, UK, with “millions and millions of animals being traded on a daily basis”.
The wildlife trade acts as a vast global network of unregulated natural laboratories, through which potential pathogens freely circulate, evolve and ultimately congregate in urban centres, says Andrew Cunningham, a wildlife epidemiologist at the Institute of Zoology in London. “It’s the scariest thing we are doing,” he says.
Before the pandemic, there was a strong emphasis on identifying new viruses in the wild. These efforts were driven by the idea that it might be possible to predict which viruses could spark major disease outbreaks. But many researchers now say that this assumption was flawed.
Increasingly, scientists are looking to human–wildlife interfaces — including markets and the trade networks that supply them — as crucial sites for the study of zoonoses, human diseases caused by pathogens that normally infect other species. A handful of research groups are now working to understand how pathogens jump between species, why some jumps cause outbreaks and others don’t, and what kinds of intervention can reduce the risks. But such work is costly, can be dangerous and demands sustained support, which has become increasingly hard to secure.
Without investing in such research, “you’re really flying blind”, says Maria Van Kerkhove, head of the emerging diseases and zoonoses unit at the World Health Organization in Geneva, Switzerland. “You’re making recommendations that may not be the most appropriate.”
Poster child
In the veterinary room of Cuc Phuong National Park in Vietnam, Tran Nam Trieu carefully lifts a Sunda pangolin (Manis javanica) onto an examination table. The creature is curled into a ball, its scales subtly rising and falling with each breath. Confiscated near the border with China in early 2023, it is now in the care of Save Vietnam’s Wildlife, a non-profit conservation organization that runs a rescue centre at the park. Delicately unrolling it, Trieu, a veterinary surgeon, reveals its soft pink belly and the wound from an amputation; its left hind leg was damaged in a snare.
The enormous demand in China for pangolin meat and scales — believed, without evidence, to cure a wide range of ailments — has made these creatures the poster child of the illegal wildlife trade. And studies of confiscated pangolins in China have detected several types of coronavirus that share up to 92% of their genome with SARS-CoV-2, the virus that causes COVID-193. Although too distantly related to have given rise to SARS-CoV-2, the viruses sometimes cause COVID-19-like symptoms in these animals and might have the potential to infect humans.
Other coronaviruses found in these pangolins are relatives of those that cause Middle East respiratory syndrome (MERS). The virus spike proteins have a feature known as a furin cleavage site4, thought to be crucial for the viruses to replicate efficiently in the respiratory tract. The presence of a similar feature in SARS-CoV-2 has contributed to the suspicion that the virus might have been engineered by researchers at the Wuhan Institute of Virology — although it could also have arisen naturally.
A live pangolin seized by the Malaysian wildlife department was probably on its way to a market in China.Credit: Bazuki Muhammad BM/JS via Reuters
Wood recognizes the “small possibility” that research-associated activities could have triggered the pandemic. But that “should not prevent us from focusing on the bigger picture”, he says: the wildlife trade poses a much greater zoonotic risk than do lab accidents.
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To gauge those risks, Nguyen Thi Thanh Nga, a researcher at the Wildlife Conservation Society (WCS) in Hanoi, and her colleagues are working to identify potential pathogens circulating in trafficked pangolins in Vietnam — a major transit hub for moving wildlife into China — and exploring how these microorganisms relate to those found in source and destination countries. Of 246 pangolins confiscated across Vietnam between 2015 and 2018 — many from the rescue centre in Cuc Phuong — 7 were infected with coronaviruses, although none had signs of respiratory or other systemic illnesses5. Partial sequences of these viruses closely resemble those of viruses found in pangolins seized in China.
Pangolins further upstream in the supply chain, however, seemed unaffected: none of the 334 pangolins confiscated from smugglers or rescued from the wild in Malaysia between 2009 and 2019 tested positive for coronaviruses6.
The increasing detection rate of coronaviruses along the supply chain is consistent with another study by WCS researchers, on rats captured and sold for food in Vietnam7. The team found that the proportion of rats that tested positive for coronaviruses was tenfold higher at the markets and restaurants where they’re sold than in the fields where they’re caught.
Trade routes
Some researchers are working to get a better handle on the human behaviours that help zoonotic viruses to thrive and spread. In 2017, Jusuf Kalengkongan, a behavioural scientist and founder of the Sulawesi Bat Conservation organization in Airmadidi, Indonesia, spent months living among wildlife hunters in villages in the province of Southeast Sulawesi. Capturing and handling bats can be dangerous work, he says, and some hunters develop fevers when wounds from a scratch or bite become infected. Rather than seeking hospital care, they typically take herbs and over-the-counter medications, he says. Village elders recalled a mysterious disease outbreak in which dozens of people died in a few weeks, Kalengkongan says.
Hung Nguyen-Viet, an animal-health specialist at the International Livestock Research Institute in Nairobi, Kenya, is leading a similar project in Vietnam. Researching trade networks, he says, is sensitive work that requires significant trust-building. A key question his team seeks to answer is: what do people do when the wild animals they capture fall ill? Some people choose to eat them, whereas others try to sell them to unsuspecting customers at a market far away, says Nguyen-Viet. Few, he says, would report it to the authorities, for fear of consequences to their livelihoods.
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Medical anthropologist Hannah Brown at the University of Durham, UK, says that attempts to regulate the wildlife trade need to take these fears seriously, or risk pushing the activity further underground. This happened when the consumption of wild-animal meat was banned in West Africa during the 2014–16 Ebola epidemic, which was suspected — but never proved — to have been caused by the eating of bats. Ten years on, says Brown, people there are still negatively affected by the policy and remain suspicious of the authorities and international researchers.
Some scientists have managed to cultivate the trust of wildlife traders in Indonesia. At the Langowan market in North Sulawesi, which sells both wild-animal meat and live animals, Tiltje Ransaleleh asks vendors about their supplies, the species they’ve sold and their origins. Beneath a canopy of red fabric that wards off the tropical Sun, Ransaleleh, a zoologist at Sam Ratulangi University in Manado, Indonesia, and her colleagues collect swab samples from bats lining the wooden stalls.
Her team has mapped an intricate network of supply chains and identified the intermediaries — who purchase wild animals (including up to one million bats a year) from hunters and transport them to markets — as a potential vehicle for disease transmission8. One insight gleaned, she says, is that festive periods are the riskiest, when sales can surge to 5 times their usual volume, with more than 10,000 bats sold in a single day at Langowan.
Sea change
These in-depth studies of trade networks and human behaviour are essential for tracking the movement of wild animals and the potential pathogens they carry, says Stephen Luby, a disease ecologist at Stanford University in California.
