Almost half of traded wildlife carry disease-causing pathogens
More than 40% of traded mammal species share at least one pathogen with humans, compared with only 6% of non-traded mammals.
Nearly half of all wild mammal species traded for food, fur, research and traditional medicines carry at least one pathogen that causes disease in humans, estimates a study1 in Science, the first to quantify the role of the global wildlife trade in the transmission of pathogens.
Many major disease outbreaks in humans, including the emergence of HIV, the 2014 West African Ebola epidemic and the COVID-19 pandemic, have been linked to traded wildlife. “We’ve known very definitively that viruses do jump from animals to humans,” says Arinjay Banerjee, a virologist at the University of Saskatchewan in Saskatoon, Canada. “What the world didn’t know was, could this be quantified? Could you actually put numbers on how many viruses make that jump?”
Comprehensive data on pathogens in the wildlife trade have only emerged in the past few years in response to the COVID-19 pandemic. They enabled Jérôme Gippet, an ecologist at the University of Fribourg in Switzerland, and his colleagues to analyse the correlation between the wildlife trade and the number of mammals that host pathogens. The study is the “first global quantitative evidence of that link”, Gippet says.
COVID-19 response
The team combined 40 years of records from three main wildlife-trade data sets with a database of species with known associations to pathogens that was developed in 2021 by ecologists contributing to COVID-19 research2. Gippet’s team focused on mammal species because of their abundance in the wildlife trade — about one-quarter of mammals are traded — and their history of transmitting pathogens to people.
To analyse the data, the team created models to predict the risk of pathogen spread through trade interactions, accounting for circumstances including the species’ evolutionary histories, how close the animals live to human communities, whether they are consumed as food and whether they are used in scientific research, all of which could influence transmission.
Of 2,079 traded mammal species, the team estimates that 41% share one or more pathogens with humans compared with just 6.4% of non-traded mammals. The trade of live animals, rather than animal products, increases the likelihood of pathogens being spread from animals to humans, too. Illegal trade of animals played only a modest part in influencing the probability of transmission. Finally, longevity mattered: on average, a species shares an extra pathogen with humans for every decade that it is present in the wildlife trade.
Gippet hopes that their findings can help to design trade regulations, in particular policies that will help to prevent future pandemics.
Terms of trade
Regulating the wildlife trade can be tricky, Banerjee says, because different countries and cultures have distinct definitions of ‘wild’ animals.
The finding that the risk of pathogen transmission did not differ significantly between legally and illegally traded animals might mean that a broad, complicated mandate for policy implementation is needed, too, Banerjee says. “I don’t think that you can go in and tell people not to eat [traded animals],” he notes. “Because the moment you clash with cultures, that policy doesn’t work.” Instead, he recommends asking communities to improve hygiene and safety at wildlife markets.
Jonathan Kolby, an applied research ecologist at the Smithsonian’s National Zoo & Conservation Biology Institute in Front Royal, Virginia, cautions against underestimating the role of domesticated animals in disease transmission — many domesticated species host a greater number of pathogens than do traded wildlife, according to data that were analysed as part of the research.
“It’s easy to kind of fall into the trap that if you were to magically stop the wildlife trade tomorrow, then there wouldn’t be more pandemics,” Kolby says. “But even if you erased all of that, we’re still left with this massive, massive domestic and international trade in domesticated animals, which is often also a source of zoonotic pathogens.”