Malaria linked to deforestation in the Amazon

Two studies conducted in the Amazon rainforest suggest a link between Amazonian deforestation and a rise in malaria cases.

The first study—carried out in the Peruvian Amazon and published in the January issue of the American Journal of Tropical Medicine and Hygiene—found evidence of a malaria outbreak in the region.

The second study, published this week in the Proceedings of the National Academy of Sciences, focuses on the clearing of forests surrounding villages in the Brazilian Amazon.

Removing trees creates sun-lit pools where mosquitoes can lay their eggs, sharply increasing the short-term risk of malaria.

Malaria is one of many diseases that have recently been tied to ecological change.

Late last year, the World Health Organization warned that the emergence of deadly pathogens such as SARS, Nipah virus, and avian influenza may also be linked to environmental degradation.

These studies indicate that preserving intact forests has important public-health implications for the Amazon and other tropical regions.

Since 1980, an estimated 320,000 km² of Amazon forest have disappeared, and the pace of deforestation and fires continues to rise.

Below is a news release from the University of Wisconsin–Madison that summarizes the research.

Scientists have long known that chronic deforestation harms forests themselves, but a new study confirms that forest loss can exert pressure far beyond environmental damage: it can also promote human disease.

A research team from the University of Wisconsin–Madison working in the Peruvian Amazon, together with Johns Hopkins University, confirmed that mosquito-to-human transmission of malaria is 200 times higher in deforested areas than in intact forest.

Their findings appear in this week’s issue of the American Journal of Tropical Medicine and Hygiene (01/06/2006).

“By dramatically altering the landscape, we are tipping the scales,” says senior author Jonathan Patz, formerly of Johns Hopkins and now a professor at UW–Madison’s Nelson Institute for Environmental Studies and the Department of Population Health Sciences.

“This is one of the most detailed, quantitative field studies in the Amazon to look directly at the potential link between deforestation and malaria.”

Over the course of a year, the team captured 56,000 mosquitoes at sites representing a range of deforestation levels.

The sites lay in and around 14 villages along a new highway that cuts through the Amazon forest between the towns of Iquitos and Nauta in northeastern Peru.

Working at night when mosquitoes feed, scientists counted how many insects landed on people.

Each site was classified as primary forest, secondary regrowth, farmland, or settlement.

“In our study area, deforestation is followed by cultivation; after the fields are abandoned, brush quickly takes over,” explains lead author Amy Yomiko Vittor of Johns Hopkins.

“Both types of converted land—farms and settlements—showed a significant rise in mosquito biting rates.”

Vittor and Patz argue that their work will help improve forecasting and control of malaria epidemics, one of the greatest global public-health threats.

“Malaria in the Peruvian Amazon has risen dramatically in recent years, jumping from a few hundred cases in 1992 to about 120,000 in 1997—roughly one-third of the population,” notes Vittor, now a fourth-year medical student at Stanford University.

The human-biting mosquito Anopheles darlingi, the main malaria vector in the Amazon Basin, thrives as trees are cleared, finding plentiful breeding sites in sunlit, shallow pools.

As mosquito numbers grow, so do the ranks of settlers attracted to newly opened land.

To separate the effect of human presence from ecological change, the researchers compared mosquito biting rates in densely populated settlements with those in sparsely populated, heavily forested areas.

Even after adjusting for the number of people, treeless sites showed much higher biting rates.

“Human presence raises the risk,” Patz says, “but human numbers alone cannot explain the surge.”

In the coming months the team plans to publish two additional papers that confirm other aspects of the deforestation–malaria link in the Amazon.

One will examine how mosquito-larval sites relate to forest clearing and to physical and biological factors such as food availability for larvae; the other will present epidemiological data on malaria prevalence among people living nearby.

Deforestation is one of the fastest landscape changes on Earth, and it could profoundly affect the spread of diseases like malaria—raising pressing questions, Patz adds.

“I see this as conservation policy intersecting with public health. Protected areas may ultimately become valuable tools in our disease-prevention strategies.”

(This summary incorporates updated statements from the University of Wisconsin–Madison.)

Source: brasil.mongabay.com

\