Two studies conducted in South America’s Amazon forest show that greater incidence of
malaria in newly settled frontier regions is related not just to the increase in human numbers, but
to changes in the landscape itself.
Over a year, various researchers collected mosquitoes at 56 sites in states of deforestation
along a new road that cuts through the Amazon in northeastern Peru. The scientists counted
how often the insects landed on humans at each site. Their results, published in the January
issue of the American Journal of Tropical Medicine and Hygiene, reveals that the bite rate from
Peru’s main malaria-spreading mosquito, Anopheles darlingi, was nearly 300 times greater in
areas cleared for logging, ranching, and other human activities than in areas with less ecological
alteration. “By dramatically changing the landscape, we are tipping the balance in a way that is
increasing the risk of malaria transmission,” says senior author Jonathan Patz, a professor at the
University of Wisconsin-Madison’s Nelson Institute for Environmental Studies.
A report in the February 14 issue of the Proceedings of the National Academy of Sciences
pointed to similar links between malaria and deforestation. The study, conducted by a different
research team in Brazil’s Amazon, attributes heightened malaria risk to the increase in standing
water that comes with tree-clearing and other ecosystem changes in the early stages of human
settlement. New pools of water create ideal egg-laying environments for A. darlingi, the
scientists note. However, once agriculture and urban development are better established in
frontier regions, this breeding habitat declines and malaria transmission rates fall. The Amazon
research aims to inform efforts to better manage malaria out-breaks, and also confirms the
importance of close collaboration between the health and conservation communities. Since 1980,
more than 50 million hectares of Amazon forest has been lost, an area roughly the size of Thailand.