Deforestation Boosts Malaria Rates, Study Finds A new study shows that tropical deforestation increases rates of malaria adding to evidence that development in fragile ecosystems can markedly harm public health. The research was published in The American Journal of Tropical Medicine and Hygiene.

Deforestation Boosts Malaria Rates, Study Finds

Deforestation Boosts Malaria Rates, Study Finds

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A new study shows that tropical deforestation increases rates of malaria adding to evidence that development in fragile ecosystems can markedly harm public health. The research was published in The American Journal of Tropical Medicine and Hygiene.


Tropical rain forests may be beautiful and exotic, but they can convey a certain dread as well. The wildlife in a rain forest often bites, stings or infects people. Recently, scientists have discovered that logging and mining in tropical forests can actually make some of those biting creatures worse. NPR's Christopher Joyce reports on new findings about mosquitoes, mercury and malaria.


Amazonians actually gave the world its first really good malaria medicine in the 17th century. It came from a tree. Europeans called it Jesuit's bark, which led many Protestants to reject it. Eventually, it caught on as quinine. Besides treating malaria, it gave birth to the gin and tonic. But quinine and subsequent anti-malarial drugs have failed to stop the resurgence of malaria in the Amazon. That's what led researchers from the US and Peru back to the rain forest near the Peruvian city of Iquitos. Amy Vittor from Stanford University was among them. She says malaria peaked in the region in 19976.

Ms. AMY VITTOR (Stanford University): They found about 120,000 cases of malaria, which amounts to about a third of the population having been infected that year. Initially, it was quite a calamity. Villages were abandoned. It was a major public health disaster.

JOYCE: The outbreak could have been simply due to more people moving into or near the rain forest, thus giving malarial mosquitoes more to bite. But Jonathan Patz, an environmental health scientist at the University of Wisconsin, noticed there were other changes in the forest: lots of tree cutting, for example.

Mr. JONATHAN PATZ (University of Wisconsin): And so we asked the question: Could this increase in malaria be related to the change in landscape, not only people moving in but actually changing the habitat?

JOYCE: Patz's team examined different types of forest--deep jungle, clear-cuts and intermediate areas with grass and shrubs. Following a procedure approved by the World Health Organization, they sent mosquito collectors out to lure insects and catch them with long straws.

Ms. VITTOR: They would arrive at 6 PM at night, roll up their pant legs, and with this homemade device would suck the mosquitoes that would land on their legs into containers.

JOYCE: That way, they only caught mosquitoes that prey on humans rather than other species that don't pose a health risk. The goal was to find out where the malaria-carrying mosquitoes--Anopheles darlingi, they're called--preferred to live. The assumption was the deep forest, but after three years and a lot of bare-legged nights, the team found that the malarial mosquitoes much preferred recently cleared areas, whether or not people were there to feed on. Patz isn't sure why. It could be the type of new plants that take over or shallow pools of water left after tree cutting or perhaps the fish ponds people built in new settlements. But the malarial mosquitoes were markedly absent from the deep, untouched forest.

Mr. PATZ: We think there's a real biodiversity issue going on here. We're actually making the dangerous mosquito more prevalent by the things we're doing to the landscape.

JOYCE: The research was published in the American Journal of Tropical Medicine and Hygiene. Malaria in the Amazon has also drawn the attention of toxicologist Ellen Silbergeld of Johns Hopkins University. She suspects that mercury used to extract gold from stream sediment might make people there more vulnerable to malaria. She found higher-than-normal levels of mercury in the blood of gold miners and people who lived downstream from mining operations.

Ms. ELLEN SILBERGELD (Johns Hopkins University): People do develop a kind of immunity to malaria, and that then prevents serious illness. And what we found was that mercury had a very strong effect in inhibiting host response to malaria.

JOYCE: Mercury may somehow compromise immunity to malaria. Silbergeld says her findings are still preliminary but are based on studies of lab animals as well as people in the Brazilian Amazon. And, she notes, there's a parallel with Patz's work: A common part of gold mining is cutting down lots of trees.

Christopher Joyce, NPR News.

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