Can Deforestation Lead to Disease?

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Land use changes in French Guiana make it possible for a potentially debilitating bacteria to thrive.

By Nathan Collins

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(Photo: cameliatwu/Flickr)

It’s obvious enough that clearcutting a forest is going to change an ecosystem—if nothing else, it can reorganize the local ecosystem. But the consequences don’t end there, as a new study highlights: Deforestation and other human effects can create the perfect conditions for emerging infectious diseases to thrive.

That’s based on a study of Mycobacterium ulcerans, which causes a disfiguring condition known as Buruli ulcers, in the forests of French Guiana. Like much of South America, French Guiana’s landscape has changed in the last several decades, the result of deforestation, expanding agriculture, and urban encroachment.

A number of studies in recent years have looked at how those sorts of human influences have affected biodiversity or the structure of food webs, but Aaron L. Morris and his colleagues wanted to know the consequences those pressures have had on the proliferation of bacteria like M. ulcerans.

The bacteria is a generalist, meaning it lives in a variety of different organisms, so the researchers first collected 3,600 fish and insects, representing 78 different species, from 17 sites around French Guiana. Forty-four of those species tested positive for M. ulcerans. Using land cover and deforestation maps, the team next looked at how the prevalence of those 44 host species changed as a function of land use.

Biodiversity was considerably lower in places where deforestation and other human actions hit hardest, Morris and his team found, which had two significant consequences for M. ulcerans: There were fewer predators that might eat the bacteria’s host species, and there were fewer prey for midlevel species—including both host species and others—to eat.

With the right balance of those two effects, the researchers found that host species were less vulnerable to predators, yet still able to find enough to eat—prime conditions for host species to thrive, and for M. ulcerans to thrive within them. The end result: a potentially serious threat to human health, driven indirectly by deforestation, agriculture, and urban growth.

“As urbanization, agriculture, and deforestation intensify, notably in tropical regions of the world (which also hosts the largest number of developing countries on the planet), similar trends for other [emerging infection diseases], as observed here for M. ulcerans, may become apparent,” the researchers write in Science Advances.

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