International wildlife trade is causing disease to spread from species to species
Animals traded in global wildlife markets are much more likely to carry diseases that can affect humans, and the risk increases the longer these species remain in circulation, according to a new study.
The analysis, published Thursday in the journal Scienceexamined decades of global wildlife trade data and found that 41% of traded mammal species shared at least one pathogen with humans, compared to only 6.4% of species not involved in trade.
Researchers also found that the number of pathogens shared between animals and humans increases over time. On average, a species contracts an additional human-infecting pathogen for every decade it is present in the global wildlife trade.
The findings suggest that wildlife trade not only exposes people to existing disease risks, but may also actively increase them over time.
“Our study is the strongest evidence to date that reducing wildlife trade will reduce the risk of pandemics,” said Colin Carlson, an epidemiologist at the Yale School of Public Health and co-author of the study.
Scientists have long linked wildlife trade to specific epidemics such as HIV, Ebola and COVID-19. Drawing on 40 years of global trade records and pathogen data, the new research attempts to quantify the relationship on a larger scale.
The results point to a broader pattern. Repeated and prolonged contact between humans and wild animals creates more opportunities for pathogens to move between species.
“What stands out most is how clearly the findings support something in disease ecology that many of us have been concerned about for years: It is not just the presence of wildlife trade that increases risk, but also the intensity and duration of contact,” said Thomas Gillespie, a professor of environmental sciences and environmental health at Emory University who was not involved in the study.
Wildlife trade, as defined in this study, includes a wide range of activities, from hunting to breeding, transportation to storage and sale. At each stage, animals are handled, confined, and often brought into close proximity to both humans and other animal species. These conditions can make it easier for viruses, bacteria, and parasites to spread.
Over time, these repeated interactions create more opportunities for pathogens to circulate, adapt, and potentially spread into human populations.
Carlson said one of the most striking findings was how strongly time in trade predicted pathogen sharing.
“The time effect in trading is the smoking gun,” he said. “We wouldn’t see this unless the pathogens jumped from animals to humans.”
He added that the findings suggest that wildlife trade, alongside deforestation, agriculture and climate change, should be considered one of the most important factors driving the emergence of diseases.
The study also found that certain forms of trading may carry higher risks. Species sold in live animal markets were more likely to share pathogens with humans than those sold as meat or animal products. Illegally traded species were also more likely to cause disease; However, researchers emphasized that the risk is not limited to illicit markets.
“Focusing on the illegal wildlife trade is not enough,” said Meredith Gore, a conservation criminologist at the University of Maryland and co-author of the study. “Pathogen transmission is a result of the general and diverse use of wildlife by humans. This includes illegal and legal trade.”
According to Gore, most international frameworks regulating wildlife trade, including the Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES, were designed primarily to protect species from overexploitation.
“There are clear and currently unmet opportunities to more directly incorporate consideration of zoonotic disease risk into existing regulations,” Gore said.
In particular, the global nature of trade complicates risk management efforts.
“Animals and pathogens don’t care about political borders,” said Jérôme Gippet, a biologist at the University of Fribourg and the University of Lausanne in Switzerland and the study’s lead author. “Without globally coordinated efforts, I don’t see how we can effectively limit these risks.”
The researchers say their findings underscore the need for a more coordinated approach that bridges conservation, public health and trade policy and addresses wildlife trade as a central element of global health risk. The study’s findings also highlight gaps in disease surveillance systems that often fail to detect pathogens circulating in wildlife before they reach humans.
“The risk is accumulating in ways that current surveillance is not capturing,” said Evan Eskew, a disease ecologist at the University of Idaho and a co-author of the study.
He said few countries systematically track which species are traded across their borders, and even fewer conduct routine pathogen screening in these animals. As a result, potential threats may go undetected until they spread through human populations.
Expanding surveillance, especially for species known to carry zoonotic pathogens, could help detect risks earlier and prevent the spread of outbreaks, Eskew said.
“We need to look for the next pandemic virus in fur farms, hunting communities, and even border control points where wildlife is imported,” Carlson said. “We are flying blind at the moment, especially in places where we have criminalized wildlife trafficking and driven it underground.”
