The Math of Wildlife Trade and Zoonotic Disease: How Pathogens Jump from Animals to Humans

Math and data science are used to understand how the wildlife trade fuels the spread of diseases that can jump from animals to humans. In this episode, Andrea Garleski talks with Colin Carlson, an epidemiologist at Yale, about how thousands of miles of animal shipment, mixed species, and dense conditions speed viral evolution. The study finds that simply being in the wildlife trade raises the chance that a traded animal harbors a pathogen that could threaten human health by about 50 percent. The discussion also covers public health implications, such as the fact that banning wildlife trade is not a simple solution and that we should focus on reducing demand, supporting community livelihoods, and improving surveillance in markets and farms to detect spillovers early.

• Wildlife trade accelerates viruses across species and facilitates jumps into humans.
• The research uses a global data set spanning 40 years across multiple animal groups and pathogens.
• Policy approaches include reducing demand, supporting alternative livelihoods, and strengthening surveillance rather than outright bans.

Overview and context

The podcast opens by reframing a familiar public health question: how does the wildlife trade influence the emergence of diseases that can infect humans? Andrea Garleski introduces the topic and introduces Colin Carlson, an assistant professor of epidemiology at Yale University, who explains that transmission is fueled not just by direct contact, but by the way animals are moved, housed in dense conditions, and combined in ways that do not occur in nature. Carlson emphasizes that this environment turbocharges viral evolution, enabling pathogens to bounce between hosts until they adapt to humans. A key line from Carlson anchors the discussion: "Wildlife trade changes that equation", highlighting how commerce reshapes dynamics that would otherwise limit cross-species transmission. "Turns out that diseases are spreading in the wildlife trade much faster than we thought," Carlson notes, signaling the urgency of a big-picture view of risk that goes beyond isolated outbreaks and anecdotal evidence.

Quote: "Wildlife trade changes that equation" - Colin Carlson, assistant professor of epidemiology at Yale University School of Public Health

Data and methods

The conversation then shifts to how Carlson and colleagues approached the question at a global scale. The study integrates data on "every species we know exists in the wildlife trade" with information on the viruses that those species carry. Carlson explains that data on wildlife trade and animal pathogens remain scarce, but the project synthesizes information across four decades, capturing how the trade has evolved from rural hunting to expansive, industrialized networks. The team tracks both pathogens and hosts across time to identify patterns that may reveal causal links rather than mere correlations, using the duration of a species' presence in trade as a smoking gun indicator of causality.

Quote: "Turns out that diseases are spreading in the wildlife trade much faster than we thought" - Colin Carlson, assistant professor of epidemiology at Yale University School of Public Health

Key findings

One of the central results is that simply being in the wildlife trade raises the likelihood that a traded animal hosts a pathogen capable of impacting human health by about 50 percent. Carlson notes that this boost is especially pronounced within mammals and that the rapidity of this spread is striking when compared with other settings, such as traditional livestock. He stresses that there is a risk of conflating correlation with causation, so the team leverages the historical timing of trade for many species to strengthen the case for a causal link. A striking quantitative smoking gun is presented: for every 10 years a species is traded, about one additional pathogen makes the jump to humans on average, a rate far faster than historical livestock disease dynamics.

Quote: "For every 10 years that a species is traded, on average, about one more pathogen makes the jump" - Colin Carlson, assistant professor of epidemiology at Yale University School of Public Health

Policy implications and solutions

The discussion turns to what is feasible in policy. Carlson argues that banning wildlife trade outright is not effective and can push activity underground, potentially worsening pathogen spread. He highlights the importance of reducing demand in high-consumption regions, investing in alternative livelihoods in wildlife-reliant communities, and improving disease surveillance in markets, farms, and supply chains. A key public health point is that workers in wildlife markets face a high risk that should be monitored with transparent, trustworthy health systems so that reporting illness does not carry criminal penalties. The overarching theme is that public health responses must be proactive and long-term, requiring decades of investment in data and surveillance infrastructure now to preempt future outbreaks.

Quote: "Criminalizing doesn't seem to work" - Colin Carlson, assistant professor of epidemiology at Yale University School of Public Health

Preparing for future outbreaks and data needs

Finally, Carlson outlines concrete steps to improve preparedness. He calls for more basic science on viruses in animals and the ecosystems they inhabit, including better understanding of how deforestation, climate change, and human activity influence spillover dynamics. The podcast stresses the need for a sustained investment in data collection and long-term research capacity, arguing that the next pandemic will likely begin in wildlife trade settings or their associated supply chains. Carlson emphasizes day-one readiness: rapid surveillance, transparent collaboration with local communities, and mechanisms to quarantine and respond without criminalizing workers who report illness. The episode ends with a call to view wildlife trade and zoonotic disease through a shared global lens, with public health as a cornerstone of policy decisions rather than an afterthought.

Quote: "we need to start looking for viruses in markets, on farms, in the people who work in these settings" - Colin Carlson, assistant professor of epidemiology at Yale University School of Public Health