Deforestation and land use change can accelerate the spread of zoonotic diseases — infectious illnesses that can spread from animals to humans — including malaria and COVID-19. While habitat restoration is crucial for addressing biodiversity loss and climate change, new research suggests counterintuitively that it can also temporarily increase the risk of certain zoonotic diseases in some areas.
Human encroachment into wild spaces for development and agriculture increases contact with disease-spreading wildlife. In Brazil’s Atlantic Forest, for example, researchers found mosquitoes were more likely to feast on humans when their natural hosts became scarce as a result of deforestation.
Despite a global push to restore degraded ecosystems, scientists have known little about how restoration affects zoonotic disease risk. To fill that gap, Adam Fell with the University of Stirling in Scotland, and lead author of a new study, conducted a large meta-analysis of scientific literature, case studies and policy reports.
“We only found something like 39 [relevant] studies, out of thousands that we looked through,” Fell told Mongabay in a video call.
The results were very context-dependent, he said. In some cases, reforestation actually increased the spread of zoonotic diseases in the short term. One explanation offered by researchers is that rodents — a common vector for infectious disease — are among the first colonizers in a disturbed landscape, and with them can come an uptick in zoonotic diseases like hantavirus.
In the long term, Fell added, ecosystems tend to find balance as larger animals, like ungulates and bobcats, return to outcompete and/or prey on rodents. That stabilization is hard to track, though, as such equilibrium can take years or decades, but most studies have limited funding and longevity, only documenting short-term outcomes.
Conversely, researchers found that restoring wetlands immediately reduced zoonotic disease transmission. Fell suspects this is likely because animals like birds and fish can return to a wetland more quickly than large animals can return to a forest. “Fish maybe then are eating the mosquito nymphs and larvae in the water,” Fell said.
“This work is vitally important in demonstrating how biodiversity fosters healthy landscapes for humans,” study co-author Luci Kirkpatrick of Bangor University, said in a press release.
A major limitation to the current study is geographic. Most studies have been conducted in wealthy countries, while the overlap between land degradation, population exposure and zoonotic disease is most common in developing countries. So, Fell’s team created the Living Evidence Atlas, which compiles existing data and provides a platform for new research as it emerges.
“It’s a first stepping stone for future research,” Fell said.
In the wake of the COVID-19 pandemic, experts urgently called for implementation of a “One Health” approach to prevent future pandemics — simultaneously addressing human, animal and ecosystem health worldwide, protecting humanity and nature and incorporating disease risk into decision-making. But the global community has made few strides in that direction.
Banner image: Tree planting in Australia. Image by John Englart via Wikimedia Commons (CC BY-SA 2.0).
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