Analysis of 40 years of data shows that mammals traded on the global market share more pathogens with humans, and that each additional decade of trade adds, on average, one more shared pathogen
Global wildlife trade is not only a threat to species and ecosystems, but also a systematic mechanism that increases the risk of pathogen transmission from animals to humans. This is the central message of a new study published April 9, 2026 in the journal Science, which analyzed 40 years of wildlife trade and mammalian pathogen data. The researchers examined how a species’ participation in the trade, the length of time it has been traded, and its presence in illegal trade or live animal markets affect the likelihood that it will share pathogens with humans.
The study focused on mammals, in part because a large proportion of zoonotic diseases that affect humans originate from this group. The researchers combined global databases of legal and illegal trade, including CITES, LEMIS and DSW, with the CLOVER database, which contains more than 190 documented associations between mammals and viruses, bacteria, fungi, protozoa and other parasites. In doing so, they built a broad picture of the relationship between wildlife trade routes and the sharing of pathogens between animals and humans.
The most striking finding is the stark disparity between traded and non-traded species. Of the 2,079 mammal species included in the traded category, 41% shared at least one pathogen with humans, compared with just 6.4% of non-traded species. Even after the researchers statistically adjusted for potential biases such as evolutionary relationship, geographic region, research effort, living in a human environment, and consumption as food, they found that traded mammals were 1.5 times more likely to carry zoonotic diseases. In other words, the mere fact that a species is traded is the strongest predictor of sharing pathogens with humans.
The study also shows that the risk is not just due to the existence of the trade, but also to its nature. Mammals traded as live animals were found to be more likely to share pathogens with humans than species traded only as products. In one analysis, species sold as live animals were found to be 1.34 times more likely to share pathogens with humans. The researchers explain that a live animal carries active pathogens with it over time, and the close contact with humans throughout the chain of collection, storage, transport, sale and possession creates more opportunities for inter-species “leakage.”
Without hygiene and veterinary supervision
As for illegal trade, the picture is more complex. When only the question of whether a particular species shared at least one pathogen with humans was examined, there was no strong evidence of an independent effect of participation in illegal trade. However, another analysis, which examined the number of pathogens shared by species already traded, found that species also appearing in illegal trade shared on average 1.4 times more pathogens with humans than species traded only through legal channels. Therefore, the conclusion is not that all illegal trade is equally dangerous, but that it may exacerbate the risk in many cases, especially when conditions of supervision, hygiene and veterinary inspection are weak or lacking.
One of the most important insights in the paper concerns time. The researchers examined more than 236,000 trade records for 583 mammal species between 1980 and 2019, and found that the longer a species has been in trade, the more pathogens it shares with humans. They estimate that, on average, a wild mammal species shares one more pathogen with humans for every 10 years it has been in global trade. This is a particularly dramatic point, because it suggests that not only species that are already considered problematic deserve attention, but also species that are not yet recognized as a clear health risk but continue to be traded over time and accumulate opportunities for disease transmission.
The importance in the post-Corona era
The researchers are careful not to establish absolute causality in each case. They emphasize that such correlational research cannot accurately describe the direction of transmission in every system, and that reverse transmission, from humans to wildlife, may also play a role. Still, they believe that the main direction is from wildlife to humans, because humans consume, transport, house, and keep wildlife in many situations, while the reverse direction is rarer. They also warn that a policy of blanket bans alone could divert activity into illegal channels if not accompanied by more advanced enforcement, tracking, and biosurveillance.
In fact, this is perhaps the most important practical lesson of the work: existing regulatory systems, primarily the CITES convention, were built primarily to protect species from extinction due to overexploitation, not to reduce epidemiological risks. The new study suggests that wildlife trade should also be seen as a public health issue. If the study findings are indeed integrated into policy, this could mean expanding oversight of live species trade, strengthening pathogen monitoring along the trade chain, and explicitly weighing zoonotic risk in international regulatory decisions. In the post-COVID-19 era, this message is likely to ring especially loud: wildlife trade is not just a nature and conservation problem, but also a key front in preventing the next pandemic.
Source: Research article inScience, April 9, 2026, DOI: 10.1126/science.adw5518.
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