Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing: a retrospective study

Abstract

Background: Deforestation and other forms of land use change are among the most pressing anthropogenic environmental impacts. In Brazil, a recent resurgence of malaria paralleled rapid deforestation and settlement in the Amazon basin, yet empirical evidence of a deforestation-driven increase in malaria remains surprisingly equivocal. We hypothesise that an underlying cause of this ambiguity is that deforestation and malaria influence each other in bidirectional causal relationships, where deforestation increases malaria through ecological mechanisms and malaria simultaneously reduces deforestation through socioeconomic mechanisms. Methods: We tested our hypotheses with a large and robust geospatial dataset encompassing 807 municipalities across 13 years and show that deforestation has a strong positive effect on human malaria incidence, controlling for variation over space and time and across gradients of land use intensification. Findings: Our results suggest that a 10% increase in deforestation leads to a 3·7% increase in Plasmodium falciparum malaria cases (about 1730 additional cases in 2008). The effect is larger in the interior and absent on the fringe of the Amazon where little forest remains. However, this strong effect is only detectable after controlling for a feedback of malaria burden on forest loss, whereby increased malaria burden significantly reduces forest clearing, possibly mediated by human behaviour or economic development. We estimated that for a 1% increase in P falciparum malaria, we would expect a 1·5% decrease in forest area cleared (about 235 fewer km2 lost in 2008). Interpretation: This bidirectional socioecological feedback between deforestation and malaria, which attenuates as land use intensifies, shows the intimate ties between environmental change and human health. Funding: US National Science Foundation Postdoctoral Research Fellowship in Biology (#1611767).