New study challenges long-held link between deforestation and malaria

A new study challenges previous findings about the links between deforestation and malaria. The study, published Wednesday in the journal World Development, finds no direct correlation between forest loss and the percentage of children with the disease in 17 African countries.

It is the first peer-reviewed study of its kind to examine the connection between deforestation and malaria in Sub-Saharan Africa, where the majority of cases involving the deadly disease are recorded.

“These results may come as a surprise to people following the literature on deforestation and malaria,” writes one of the study’s authors, Jonah Busch, Chief Economist with Earth Innovation Institute.

Ecological studies have found that the loss of tree cover creates conditions including warmer temperatures and more standing water that are conducive to the spread of malaria-transmitting mosquitos. Busch and co-author Sebastain Bauhoff, with Harvard’s T.H. Chan School of Public Health, aren’t challenging those findings. But they contend that more malarial mosquitos may not mean more malaria cases in humans.

Previous studies, including seven in Brazil, where deforestation rates remain persistently high, have drawn a direct link between deforestation and malaria rates. But Busch and Bauhoff theorize that differences in how deforestation occurs on different continents can affect the degree to which the disease spreads.

In Brazil, deforestation is driven largely by the rapid expanse of agriculture into frontier regions and is accompanied by an in-migration of new arrivals to recently cleared lands. Under these conditions, “frontier malaria” can spread more rapidly. In Africa, forest loss involves predominantly small-holder farmers in settled and relatively stable socio-economic conditions.

These differences can in turn have an impact on such factors as rates of human exposure and immunity, as well as resources like adequate housing and the availability – or lack thereof – of existing health services, all of which can influence the rate of infection.

The authors argue the findings indicate that efforts to combat the disease in Africa, where 88 percent of malaria cases occur worldwide, should continue to focus on conventional methods, including insecticide-treated bed nets, indoor spraying and clinical treatments, among other proven interventions.

While there are important environmental reasons to prevent forest loss, including carbon capture and clean water provision, they note that mitigating against the spread of malaria in Africa may not be one of them.

The results are almost certain to add to the ongoing debate over the relationship between deforestation and malaria. To bolster their findings, the researchers employed a pre-analysis plan, drafting their hypotheses, methods and variables in advance and making them public. Such steps are common to clinical studies, but relatively new to the social sciences.

Busch notes taking such measures ensured methodological integrity no matter what the findings, keeping the researchers true to their pre-specified approach in the face of at times unexpected results.

And given the threats posed by deforestation and malaria, adds Busch, it was important to ensure confidence in the findings and that they reach as broad an audience as possible.

“At stake in a full and accurate understanding of deforestation and malaria,” he notes, “are the lives and health of millions of people and the conservation of millions of hectares of forest.”

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