Wildlife trade drives animal-to-human pathogen transmission over 40 years.

The wildlife trade affects a quarter of terrestrial vertebrates and creates opportunities for cross-species pathogen transmission, but its precise role in shaping animal-human pathogen exchange remains unclear. In our analysis of 40 years of global wildlife trade data, we show that traded mammals are 1.5-fold as likely to share pathogens with humans as nontraded mammals, and that illegal and live-animal trade further exacerbate pathogen sharing. Time spent in trade predicts the number of zoonotic pathogens that a wildlife species hosts. On average, a species shares an additional pathogen with humans for every 10 years it is traded. Editor's summary: The closer and longer the contact between species, the higher the chances of transmission of pathogens. This rule of thumb applies to human-to-human contacts as well as contacts with other species. Gippet et al. examined trade data for wildlife species from the past 40 years and showed that the longer a species had been legally traded, the greater the likelihood that humans and the trade species will share some sort of pathogen (virus, bacterium, fungus, or parasite). The authors estimate that traded wildlife species share one additional pathogen with humans for every decade in the global wildlife market. —Caroline Ash INTRODUCTION: The wildlife trade is an important form of human-animal interaction that affects around a quarter of all mammal species. Multiple trade-related activities, including harvesting, breeding, warehousing, transport, market placement, and end use, create opportunities for cross-species pathogen transmission. As such, the human-animal interactions occurring throughout wildlife trade networks can lead to infectious disease outbreaks in humans, including epidemics and pandemics with major socioeconomic impacts. Although several high-profile outbreaks, including the emergence of HIV, the 2014 West African Ebola epidemic, the 2003 mpox outbreak in North America, and the COVID-19 pandemic, have been linked to traded wildlife, the long-term impact of the wildlife trade in shaping pathogen exchange between humans and wild animals remains unclear. RATIONALE: Research on the determinants of host-pathogen interactions has mostly focused on ecological and evolutionary drivers in the absence of human influence, and disease dynamics in the wildlife trade remain poorly studied. In theory, traded wildlife should be more likely to share pathogens with humans because frequent and close contact increases opportunities for cross-species transmission. Therefore, the longer and more intensely species are traded, the more pathogens they should share with humans. We empirically tested whether traded species are more likely to share pathogens with humans than nontraded species, how live-animal markets and illegal trade modify this risk, and whether time spent in trade predicts the number of zoonotic pathogens hosted by wild animal species. RESULTS: Focusing on mammals, we showed that, among 2079 traded species, 41% share at least one pathogen with humans, compared with 6.4% of nontraded species. Traded mammals are about 1.5-fold as likely to be zoonotic hosts, even after controlling for phylogeny, geography, research effort, synanthropy, and consumption by humans. Synanthropic species and those consumed as food are also more likely to share pathogens with humans, but these effects are weaker and partly mediated by trade and research effort. In addition, species traded live are more likely to share pathogens with humans, and illegally traded species share more pathogens with humans than those traded only legally. Finally, a temporal analysis of 583 mammal species listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) over 40 years (1980-2019) shows that time in trade is a key predictor of zoonotic pathogen richness. On average, a wild mammal species shares one additional pathogen with humans for every 10 years it is present in the global wildlife trade. CONCLUSION: Wildlife trade is a major driver of animal-to-human pathogen transmission. Trade status strongly increases the probability that a mammal is a zoonotic host, and cumulative time in trade predicts how many pathogens it shares with humans. Live-animal markets and illegal trade further amplify these risks. These findings highlight that cross-species pathogen transmission is an inherent consequence of diverse uses of wildlife by humans and underscore the need to strengthen biosurveillance and integrate zoonotic risk considerations into wildlife trade regulations to help prevent future pandemics. Wildlife trade drives zoonotic pathogen transmission over 40 years.: By analyzing 40 years of international trade in wild mammal species, we show that the number of zoonotic pathogens hosted by a wildlife species increases with the number of years it has been present in trade: On average, a species shares an additional pathogen with humans for every decade it has been present in trade. PHOTO MONTAGE WAS CREATED BY P. GIPPET-VINARD FROM PICTURES (MODIFIED FOR THIS ILLUSTRATION) FROM ENVATO ELEMENTS (SERVAL, MONKEY, AND PELTS) AND FROM KOTKOA ON FREEPIK (HUNTING TROPHIES) [ABSTRACT FROM AUTHOR]