As the new coronavirus continues to turn the world upside down, crashing economies and overextending health care systems, epidemiologists and infectious disease experts are increasingly focusing on how to prevent the next pandemic, rather than solely reacting to the current one.
Covid-19 has already taught many lessons about response and resilience to disease, but perhaps chief among them is that if we do not significantly alter our relationship with the natural world, the next pandemic could be not just around the corner, it could be worse.
A report released by the United Nations Environment Programme (UNEP) and the International Livestock Research Institute (ILRI) last month makes the case for focusing on the causes of pandemics instead of treating the diseases as they emerge, an argument echoed by many in the field, including Dr. Hana Akselrod, an infectious disease specialist, and author David Quammen, who has written extensively about so-called zoonotic diseases.
"There have been literally thousands of reports on Covid," according to Dr. Delia Grace Randolph, a veterinary epidemiologist and lead author of the report, "but many of those are focused on the response. We're looking at rather more fundamental things—why and where did this pandemic come in the first place?"
What is a Zoonotic Disease?
The term "zoonoses" may be new to many people, but it has been around since the 1800s. A zoonotic disease is one that transmits, or "spills over," from the animal world into the human world. Covid-19 is a zoonotic disease, as are Ebola, HIV/AIDS, MERS, and even Lyme disease. Nearly 6 out of every 10 known infectious diseases are transmitted by animals, and a staggering 75 percent of new and emerging diseases are zoonotic in nature.
David Quammen, author of the bestselling 2012 book Spillover: Animal Infections and the Next Human Pandemic, was not surprised when he heard that a novel coronavirus had appeared in China early this year.
"It is peculiar to have published a book on this subject in 2012 that essentially predicted this pandemic," Quammen said. "Not because I was prescient. But because the scientists that I talked to saw it coming."
Hana Akselrod, an infectious disease doctor at George Washington University School of Medicine in Washington, spent this spring on the front lines of the Covid-19 crisis. An HIV specialist by training, she was also unsurprised by the arrival of Covid-19. "An event like this is something scientists have been warning about for, literally, decades," she said.
The reasons for the emergence of zoonotic diseases, Akselrod, Quammen and Randolph said, are written in the way we interact with the animal world and the impact we have on our environment.
"When human and animal populations are both stressed, if that's from disease, from lack of food, from crowding and from changing living conditions and ecology that's related to a changing climate," Akselrod said, "that kind of puts us and them together in a pressure cooker environment as far as disease transmission is concerned."
Because globalization has increased international trade and travel, it's also far easier for diseases from wild animals to spread quickly around the globe.
"We are disrupting wild ecosystems at a scale far beyond anything that we have ever done, and we are traveling more quickly" said Quammen. "So when a new virus gets into a human population in some remote corner of the world, it doesn't stay there as an obscure affliction of the people in that village. In more cases than not, it gets to a town, it gets to an airport. And in some cases it gets around the world."
He added, "So the spillovers that happen are happening probably with greater frequency, but they're also more likely to turn into big events than ever before."
Climate Change and Other Causes of Zoonotic Diseases
The UNEP/ILRE report outlined seven "deadly drivers" of zoonotic diseases, all of which have to do with the ways humans interact with animals and encroach into the natural world. That list includes climate change, which Randolph said is both a facilitator and a driver of disease. But global warming is indirectly related to the other drivers, as well, including increasing demand for animal protein, unsustainable agricultural intensification, unsustainable utilization of natural resources and increased travel and transportation, all of which also contribute to climate change. Others, such as the increasing exploitation of wildlife, are more likely to occur in a warming world.
Climate change rearranges the distribution of pathogens and the vectors that can carry a disease from one species to another, as it tends to make the world "wetter, warmer and more unpredictable," according to Randolph. That can create new breeding grounds for vectors like mosquitoes, which, in 2015 and 2016, carried the Zika virus to much of North and South America, and as far away as parts of Europe and New Zealand.
"Insects are exquisitely sensitive to environmental changes," said Akselrod, pointing out that Lyme disease is another zoonosis that shows signs of a climate change-driven spread. As the world warms, ticks have moved northward from New England into Canada.
Climate change can have other impacts on zoonotic disease transmission, Randolph said. It "makes people more vulnerable, and more vulnerable people are poorer and less able to seek and pay for health care and to take good good care of themselves and their children," she said.
History clearly shows this trend, Akselrod said. "The people who don't have access to resources to control their surroundings and their own lives have been on the deep end of every epidemic through the ages," she said.
Staunching the Spillovers
Today, a vision of even deadlier, more frequent and, possibly, simultaneous disease outbreaks haunt people around the world, but Akselrod, Quammen and Randolph said that future doesn't have to come into being.
"We continue drawing resources out of the natural world: we cut down trees, we go into tropical forests, we build timber camps, we extract minerals, we extract fossil fuels," Quammen said. "As we suck these resources from the natural world, we draw the viruses of the natural world toward us too."
But, he added, "We have the money, we have the resources, we have the science, we have the public health expertise. If only we have the individual willingness and the political will collectively to stop these things, then we can prevent future spillovers and outbreaks from turning into future pandemics."
The UNEP report provides something of an instruction manual for breaking the chain of transmission, much of it in an approach called One Health, which essentially sees pandemics as interconnected between many layers of society—from rural villagers and veterinarians to agricultural workers and physicians—with the prevention of outbreaks requiring coordination and participation across all of them.
Another way to look at it, Randolph said, is "if you can prevent the disease in the animal, and if you can prevent the disease in the environment, it will never get to the person."
This approach can not only save countless human lives, Randolph said, but will be cost-effective in the long term. A recent report in the journal Science estimated that the cost of preventing the next pandemic would be just 2 percent of Covid-19's economic damage.
Ultimately, these experts agree, averting the coming pandemics requires no longer thinking of Covid-19 as a one-off event.
"If we continue on the track we are on today," Askelrod said, "there will be more and more events like this and they will be devastating and they will define us."