In the early 1990s, Kinari Webb took a year off college to join a Harvard researcher studying orangutans in Indonesias's rainforested Gunung Palung National Park.
As the aspiring primatologist dissected dung samples to determine the animals’ feeding habits, the buzz of chainsaws and the thwuuuump of falling dipterocarp trees—some of the tallest species in the world, routinely rising more than 200 feet—broke through the great apes’ calls. Despite federal protection for the land, loggers illegally, and extensively, felled trees throughout the preserve, which sits on the western coast of Borneo. In fact, some of the local research assistants who helped Webb’s team uncover scat were former loggers, including a man named Tadyn (like most natives, he does not use a surname). One day, he came to her with a gaping cut in his hand, surprisingly distraught for someone who had once fought an attacking sun bear—and won. “It wasn’t that big of a wound,” Webb recalls. “His machete had slipped. But he had terror in his eyes, the most I’ve ever seen in a person.”
For locals, a minor injury could be life-threatening. They didn’t have access to tetanus shots or antibiotics, and getting to the nearest hospital entailed a day’s journey by dugout canoe, followed by another on a motorboat and another in a car. Accessing treatment incurred costs that were astronomical relative to their incomes, so, around Gunung Palung, medical emergencies brought out the chainsaws. Because the protected areas are off-limits to the wide-scale clearing that has created lucrative palm oil plantations across Borneo, villagers often cut and sell the virgin trees. One resident Webb met downed 60 to pay for a relative’s cesarean section. As Tadyn told her, “We don’t have any other choice.”
As she continued her work in the Bornean forests in the intervening decades, Webb would discover another consequence of the tree-chopping economy: Pervasive illegal logging can also threaten public health. Disease ecologists increasingly agree that human disturbance of wildlands increases the risk of zoonotic diseases—pathogens that jump from animals to people—which helps explain why spillover events, as epidemiologists call them, are on the rise around the globe. The number of fauna-borne outbreaks quadrupled between 1980 and 2010, according to a 2014 analysis from Brown University, and the Centers for Disease Control and Prevention says that three-quarters of human illnesses discovered in recent decades originated in wildlife. The US Agency for International Development’s PREDICT program estimates that animals harbor some 700,000 as- yet- unidentified infectious baddies with the potential to make the jump to people. It takes only one of those to change the world.
We’ve traded pathogens with other creatures for millennia, but in the past, if an outbreak did occur, geographic spread was limited. Not so in the era of globalization and population booms. Ecological disturbance—whether from deforestation, natural disasters, or climate change—often puts both people and animals on the move. Species that were not typically in contact with one another may suddenly find themselves in close proximity and sharing pathogens.
Consider the Black Death, which in the 1300s killed up to half of Europe. In 1925, Malaysian physician Wu Lien-Teh confirmed the source of the infamous disease—fleas in the fur of Central Asian rodents called tarbagans—which enabled later generations of scientists to unravel the social and environmental factors that conspired to spread the deadly illness. The advent of agriculture in the region offered an ample food supply, spurring a spike in the rodents’ population; demand for their furs made the creatures a lucrative target for hunters; and trade along the Silk Road eventually brought the plague to Europe.
More recent zoonotic spillover events—including AIDS, Ebola, MERS, and SARS—have followed a similar pattern, and COVID-19’s story comes from the same playbook. Some epidemiologists suspect that horseshoe bats passed SARS-CoV-2, the virus that causes the illness, to Sunda pangolins, armadillo-like creatures poached in Southeast Asian countries and sold live in markets in the now-infamous Hubei province, before the disease was ultimately transmitted to us. Brazilian biologist Gabriel Laporta was among the first to suggest that deforestation may have driven the bats and pangolins to nest in the same caves—a novel opportunity for the coronavirus to hop species.
Webb doesn’t know what unknown diseases might be lurking in the forests of Borneo (Nipah virus, which inspired the movie Contagion, hails from the region), but she has spent much of her career developing a unique conservation model that may keep zoonotic bugs in the shadows, rather than boarding planes. Her goal is to help local communities avoid risky practices surrounding logging, such as eating wild animals (often referred to by Westerners as bushmeat).
This mindset puts Webb squarely within the emerging field of planetary health, an interdisciplinary movement of scientists who view the destruction of the environment as a top public health threat. “We need to think differently about how we manage our interface with wildlife,” says Samuel Myers, director of the Planetary Health Alliance, a consortium of more than 200 universities, NGOs, research institutes, and government entities. People, he says, often intrude into habitats because “they’re trying to feed their families, so we need to give them an alternative.”
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