Deforestation is a key driver of that biodiversity loss. In 2019, the tropics lost close to 30 soccer fields’ worth of trees every single minute. A third of those were in primary, previously undisturbed rainforests. That rapid clearing of forests is drastically impacting the emergence of zoonotic infectious diseases, says Peter Daszak, president of EcoHealth Alliance, an organization that conducts research and outreach on emerging diseases and their underlying causes, and a frequent WWF collaborator.
How does this happen? “As you send people into forests, to build a road or do some logging, workers need food,” says Daszak. “Without a good food supply, they’re going to go get bush meat.” The consumption of wild meat is one risky interaction point where the transfer of disease from animal to human can take place.
Hunting—and the associated trade in live wild animals, often fueled by foreign demand— also puts humans in direct contact with wildlife and the pathogens that tag along for the ride. But “while diseases might be spread by wildlife trade,” Terrana says, “the enabling conditions can often be traced to tropical deforestation and habitat fragmentation.”
Infectious diseases can also be spread by vectors—the disease-spreading “middlemen” that can pass pathogens between species; often, the culprits are biting insects like mosquitoes. And many of those disease-carrying insects breed in puddles—the kind caused when deforestation disrupts waterways and carves shallow ruts into a scarred landscape, collecting rainwater in stagnant pools.
We already know that vector-borne diseases like Zika and dengue emerged from forests, carried by mosquitoes. As more land is cleared, different species of mosquitoes are exposed to humans in the fringe-forest areas—and new opportunities for disease transmission arise.