The Next Pandemic Might Already Be Taking Shape at the Edge of the World’s Vanishing Forests

Here’s what you’ll learn when you read this story:

• Outbreaks of diseases transmitted by insects and other animals can quickly turn into epidemics or pandemics, but researchers wanted to find out how they emerge.
• The researchers studied datasets from multiple outbreaks and discovered that various anthropogenic factors, such as urbanization, are aggravating the problem.
• While outbreaks will only increase if temperatures rise, making efforts to mitigate the human destruction that has been causing climate change could possibly prevent future outbreaks.

Before a disease snowballs into an epidemic—or worse, a pandemic—where does the outbreak begin? The answer, it turns out, may be us.

When Homo sapiens burst onto the scene and began modifying ecosystems, often in destructive ways, infectious diseases that would have otherwise stayed contained in forested areas or within insect networks instead began spilling over into human populations. Human activity has also spurred climate change, which in turn has bred even more diseases. Rising temperatures have fueled hotbeds of viruses and bacteria that rely on insects to transmit them. Swarms of mosquitoes, which thrive in hot and humid environments, have been vectors for illnesses such as Zika virus and malaria. Other diseases carried by animals have been unleashed by deforestation.

“Human-driven ecosystem changes and human–wildlife–livestock contact can drive the emergence of zoonotic and vector-borne diseases,” said an international team of researchers investigating this Anthropocene phenomenon in a study recently published in Nature. “But how much these processes shape landscapes of outbreak risk is poorly understood.”

Disease outbreaks tend to occur most often in regions where people and livestock live adjacent to forests and other ecosystems that have been adversely affected by anthropogenic developments and climate change. Environmental shifts driven by human damage can leave animals more vulnerable to infection and push them into new territory, where insect-borne diseases can prove lethal. That can mean higher rates of arboviruses, the insect-borne family that includes dengue and several types of encephalitis. It can also mean more tick-borne Lyme disease and more coronaviruses. Worldwide, outbreaks have been steadily rising.

While there are preventative measures such as vaccines, and also many initiatives to reduce greenhouse gas emissions and restore ecosystems, this problem won’t disappear in the blink of an eye. Evidence about how these diseases emerge and spread is still thin. Agriculture, deforestation, climate change, habitat destruction, and urbanization are all part of the picture, but the conditions that turn those pressures into an outbreak remain poorly understood. Pathogen life cycles vary. So do social vulnerabilities and the rate of contact between people and animals, which differ by region and population. Earlier work suggests outbreaks surface where social and ecological pressures converge—which leaves a harder question: which pressures matter most?

To find out what really heightens outbreak risk, the researchers analyzed datasets from outbreak events across many locations and identified five contributing factors. The first is detection: how much of a region is urbanized and how long it takes to reach the nearest healthcare facility, both of which shape how quickly an outbreak is spotted and contained. Next come socioeconomic conditions, including social vulnerability and livestock density. The remaining three are ecosystem structure (particularly how much biodiversity has been lost to human activity), land uses such as mining and development, and climate change. The weight any single factor carries depends on the region.

The team set out to answer three questions: whether human influence on outbreak intensity can be separated from reporting bias and unrelated noise, whether some forms of environmental change trigger outbreaks more reliably than others, and how strong the evidence for disease emergence really is. The answers could shape future intervention strategies. On the first, they found that the world’s apparent outbreak hotspots may partly reflect where researchers have looked—urban areas are easier to reach, and rural regions have long been overlooked. They also found that access to healthcare improves both detection and response, and that a pathogen’s mode of transmission affects how severe an outbreak becomes.

“We find evidence of a strong and consistent anthropogenic fingerprint on [diseases], suggesting that over the coming decades, risk is likely to increase unless there are substantial shifts in human activities,” the researchers concluded. “Efforts to mitigate climate change will help slow [many] diseases, with the greatest impacts felt over the coming decades.”