Agricultural drivers were responsible for 50 percent of deadly zoonotic diseases that emerged in human populations—”proportions,” they wrote, “that will likely increase as agriculture expands and intensifies.” Global population has climbed in the past 60 years, but so have global appetites for livestock-based foods, including beef and dairy, which have a bigger carbon footprint.
As panicked consumers flock to grocery stores, emptying shelves in preparation for homebound quarantines that could last for weeks, the coronavirus pandemic is revealing an alarming longer-term concern about the world’s growing appetites and the stresses they impose on a warming planet.
Zoonotic diseases—those that spread between animals and humans—represent the biggest proportion of new, emerging diseases like COVID-19, which scientists believe originated in bats.
Most of these diseases originate in wild animals whose forest habitats are being destroyed, largely for agriculture and mostly for cattle or the crops used to feed them.
As global population climbs, and demand for food along with it, these habitats will continue to disappear or change. And the animal species that proliferate in these transformed landscapes, especially bats and rats, are uniquely good at passing on deadly viruses, researchers say.
In other words, our growing global appetite will stoke populations of the very species best designed to kill us with new viruses.
Climate change presents one of the greatest challenges to global food production, with drought, flooding and increasingly unpredictable weather being only the most obvious problems. It will also force agriculture into new areas, as some regions become too hot or wet, which probably will mean yet more conversion of natural habitat into crop land.
With the global population expected to soar to 11 billion people by 2100, humans will need much more food and much more land to produce it, accelerating the loss of biodiversity that helps shield people from zoonotic disease.
“Population growth is on steroids and we’re blowing the hinges off the doors in terms of risk,” said Dennis Carroll, a prominent “virus hunter” who has led government programs tracking viral epidemics. “Land-use change is the biggest driver of risk.”
Carroll helmed the U.S. Agency for International Development’s emerging threats unit for 15 years, and also launched the agency’s Predict program in 2009 in response to the 2005 avian influenza outbreak. The project, which investigated the sources of new zoonotic diseases, discovered 2,000 new viruses and worked in 30 countries in Asia and Africa.
The Trump administration ended funding for the project in 2019, along with shelving other key efforts for studying the spread of infectious diseases.
But researchers, including Carroll, say even had it continued, the program and other efforts underway are inadequate to the task of tracking and managing these viral outbreaks, which requires a coordinated global response
“There was a lot of good work done,” said Christopher Whittier, a specialist in infectious diseases and wildlife at Tufts University, who was involved in the Predict project. “But it’s a relative drop in the bucket compared to what the world needs to be doing.”
The shuttering of the program at USAID is part of a broader pattern in which the Trump administration has attempted to sideline research into zoonotic diseases, like COVID-19.
In an analysis released Tuesday, the Environmental Data and Governance Initiative said that the Centers for Disease Control and Prevention, the “nation’s flagship disease fighting agency,” has suffered a “slow but corrosive decline in available resources” under the Trump administration, with the yearly budget dropping 4 percent between 2016 and 2019.
The administration’s annual attempts to cut the CDC’s budget have mostly been turned back by Congress, but the Trump administration has taken direct aim at the agency’s Emerging and Zoonotic Disease program every year since Trump took office. Though the budget for the program has nearly doubled, to about $635 million over the past decade, Trump proposed cutting it by 20 percent in the current fiscal year and in 2021. The administration also sought to stop funding for a global health security program co-run by the CDC and USAID, and successfully got rid of most of CDC’s staff working on global health security in China, the analysis found.
‘Climate Change is a Stressor’
Last year, in a landmark report on the state of global ecosystems and biodiversity, the United Nations Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), projected that 1 million species could be extinct within decades. The report called the loss of biodiversity as great a threat to the planet as climate change—and pointed to agriculture as the key driver.
“We have a population problem and a consumption problem. It’s not either or,” said Felicia Keesing, an ecologist at Bard College who has written extensively on biodiversity and infectious diseases.
A changing climate complicates the situation. “Climate change is a stressor. If a species has reduced range because of habit conversion or fragmentation, and then that species experiences atypical climate signals—like spring happening earlier—that limited range may be beyond its tolerance, so climate change can be a driver of biodiversity loss,” Keesing explained.
She added, “The connection with disease is: The species that thrive when biodiversity declines are the species that are best at transmitting diseases.”
Larger animals, especially predators, need bigger ranges to survive, so when their habitat shrinks or fragments or disappears altogether, they die off. These animals typically have fewer offspring and live relatively long lives.
But “weedy” species, like rats and bats, breed rapidly.
“They have a live-fast-and-die-young history. They crank out tons of babies and then they drop dead,” said Richard Ostfeld, an ecologist with the Cary Institute of Ecosystem Studies, in Millbrook, New York. “They tend to allocate their energy into breeding rather than living a long time, and they tend to have permissive immune systems and are breeding grounds for pathogens.”
As species’ habitats shrink or change, the animals move into new and closer quarters.
“Creatures big and small, on land and in sea, are being pushed to the poles to get out of the heat,” said Aaron Bernstein, the interim director of The Center for Climate, Health and the Global Environment at the Harvard T.H. Chan School of Public Health “That makes them come into contact with animals that they wouldn’t otherwise.”
Given that scientists believe the new coronavirus came from bats, Bernstein added: “If you took a bat and gave it lots of places to call home, the odds of it spreading a virus to its fellow bats is relatively smaller than if you locked it up in a phone booth with 100 other bats.”
Researchers Link Agriculture to ‘Spillover’
All of these pressures—growing population, increased demand for food, shrinking habitat, species movement and climate change—will lead to more “spillover,” with animal diseases spreading to humans.
“Feeding 11 billion people—and the associated increase of land converted to agricultural production and livestock grazing—is expected to cause a surge” in contact between humans and animals, “increasing the likelihood of ‘spillover’ events,” Ostfeld and co-authors wrote in a paper in Nature Sustainability last year.
Ostfeld and his co-authors reviewed scientific studies going back to 1940, finding that agricultural drivers were responsible for 50 percent of zoonotic diseases that emerged in human populations—”proportions,” they wrote, “that will likely increase as agriculture expands and intensifies.”
And agriculture will do just that, researchers say.
Global population has climbed in the past 60 years, but so have global appetites for livestock-based foods, including beef and dairy, which have a bigger carbon footprint.
“There’s this insidious cycle. Climate change is driven, obviously, by changes in gases. Those are driven by animals, both directly and indirectly, as you clear out space for them to graze or for the grains you feed them,” Carroll said. “That’s a very strong connection between climate change and these diseases.”
Projections suggest that the appetite for meat will only climb more, especially in the developing world.
Those predictions underlie recent suggestions, in reports from academic and government sources, including the United Nations, for people to consume less beef and dairy, especially in developed countries—for reasons of both climate and biodiversity.
Researchers continue working to identify just how the new coronavirus originated and spread, but they know that it stems from a “wet market” in Wuhan, China, and mostly likely spread from a bat through an intermediary, possibly the widely-trafficked pangolin.
Like the avian influenza of 2005, it can be traced to places where humans consume or slaughter animals that have been crammed together in unnatural ways.
“People were responsible for transporting animals into brand new habitats, meaning a wet market, where species that never, ever come into contact in nature, come together in proximate and very unhygienic situations, surrounded by gazillions of people,” Ostfeld said. “It was human activity, clearly, that created the species jump.”
And the more human appetites and climate change interfere with natural habitats, the more that will occur.
“We’re not doing anything at rates to suggest anything will get better,” Keesing said. “The assumption is that we’ll only see this happening at a greater rate, because we’ll continue to see habitats disappear.”
Biodiversity loss, much like climate change, can feel like an abstract problem to the humans causing it. But experts hope that the immediacy of COVID-19 could at the very least help reinforce how dangerous these intertwined problems are.