To prevent the next pandemic, we might need to cut down fewer trees

Study weighs costs of reducing virus spillover from animals against the toll of disease outbreak

Marburg cave in Uganda

Most new infectious diseases come from animal viruses jumping to humans, such as Marburg hemorrhagic fever, which researchers traced to a bat population in this Ugandan cave. A new analysis weighs the economic toll of the COVID-19 pandemic against the costs of reducing the likelihood of these “spillover events.”

Photo courtesy Amman/CDC

Reducing tropical deforestation and limiting the wildlife trade might be cost-effective ways of stopping pandemics before they start, a new analysis finds.

About once every two years, a virus jumps from animals to humans, raising the specter of a pandemic like COVID-19. These “spillover events” are becoming increasingly common as humans encroach further into the natural world and have originated some of the worst outbreaks in recent memory, including SARS, Ebola, HIV and likely the new coronavirus too.

Whether a spillover explodes into a pandemic depends on many factors, including qualities of the virus itself and how humans respond to it. But some biologists argue that pandemic preparedness should start with reducing the likelihood of spillover events in the first place, by fighting deforestation, monitoring farmed animals and limiting the wildlife trade. 

Such interventions would cost roughly $20 billion to $30 billion each year, according to an analysis in the July 24 Science. That price tag pales in comparison to the estimated global cost of COVID-19, which tops $5 trillion U.S. dollars in lost gross domestic product for this year alone.

“COVID has killed hundreds of thousands of people and caused massive disruption to the economy,” says coauthor Stuart Pimm, a conservation biologist at Duke University. “We’ve shown that there are lots of smart, relatively cheap things we can do now to reduce the risk of another catastrophe like this one.”

Forest edges represent a major front line for spillover events. As humans clear swaths of forest for agriculture or roads, forest edges multiply, increasing spillover risk from once-isolated wildlife to humans and livestock. While such forest loss is accelerating in many places, some countries have taken action. From 2005 to 2012, Brazil implemented land-use zoning and paid people not to chop down forests, reducing deforestation by 70 percent.

Based on the costs of those and similar programs, the researchers estimate that deforestation rates could be halved globally with investments of $1.5 billion to $9.5 billion a year, reducing spillover risk while preserving biodiversity and reducing carbon emissions.

Wildlife markets and the illegal wildlife trade also bring humans into contact with wild animals and their viruses. The United States is a major market for exotic and sometimes endangered pets shipped from all over the world, increasing human exposure to wild animals (SN: 9/14/18). In China, wildlife farming is a nearly $20 billion industry that supports cultural dietary preferences, but also may raise the risk of spillover events. For instance, SARS likely emerged in a Chinese wildlife market.

But ending the wild meat trade in China alone would cost far more than halving deforestation. The researchers suggest it would cost around $19 billion a year to counter the potential profits from the lucrative wild meat market. Monitoring programs that might screen wild animals for viruses in potential hot spots would cost an additional $120 million to $340 million per year. In China, the government banned the trade of wildlife trade and consumption in February, though the details and long-term prospects of that ban remain uncertain.

Pimm and his colleagues estimate that other interventions, such as monitoring viruses in livestock, would cost hundreds of millions of dollars each year.


Weighing costs

This table shows a breakdown of the estimated annual costs of various measures to reduce the likelihood of spillover events, where animal viruses jump to humans, against the estimated global gross domestic product lost this year to the COVID-19 pandemic.

Cost of COVID-19 vs. annual maximum costs of pandemic prevention measures
Global GDP drop in 2020 from COVID-19$5.6 trillion
Total maximum prevention costs$31.2 billion
End China’s wild meat trade$19.4 billion
Cut deforestation in half$9.59 billion
Curb spillover from livestock$852 million
Curb spillover from wildlife$340 million
Early disease detection$279 million
Monitor wildlife trade$750 million

Source: A.P. Dobson et al/Science 2020


To justify those costs, the interventions would need to reduce the chance of a pandemic by 27 percent in a given year, the analysis finds.

Exactly how much these interventions reduce spillover risk is hard to determine, Pimm says. “We’re not going to stop [spillover events], but we’ve shown that even if these interventions make pandemics less likely by a smidgen, it’s a cost-effective solution.”

“It’s great to have another piece of evidence on the pile for why pandemic prevention matters and why it’s cost-effective,” says Colin Carlson, a global change biologist at Georgetown University in Washington, D.C., who wasn’t involved in the study. But he worries that focusing on reducing spillover events might detract from much-needed investments in public health infrastructure. 

“Deforestation and the wildlife trade do cause spillover, but they don’t cause pandemics,” he says, while noting that reducing these activities may reduce pandemic risk. “Pandemics happen because of lack of governance, sensible public health interventions and surveillance.”

Carlson is especially skeptical of the cost-effectiveness of ending the wildlife trade. “The idea that we would spend two to 10 times as much ending the wildlife trade in one country as we’d spend cutting deforestation in half globally should tell us something about where the easy fixes are,” he says. Efforts to curb wild meat consumption in response to disease outbreaks can also harm local populations who rely on wild meats for proteins and decrease trust in public health, which happened in the 2015 Ebola outbreak.

While the wildlife trade is a source of spillover, Carlson says the emphasis placed on it often outstrips the evidence. Despite many suggestions that the coronavirus came from a wildlife market in Wuhan, that link isn’t yet widely accepted.

Pimm and his colleagues agree that controlling the wild meat trade should take local needs into account, and that some of the interventions they propose are likely more cost-effective than others. “But these actions would be a prudent investment for national and international security,” Pimm says. “And none of what we propose is expensive in comparison to countries’ military spending for security.”

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