Does Deforestation Increase Malaria Prevalence? Evidence from Satellite Data and Health Surveys

Abstract

Deforestation has been found to increase malaria risk in some settings, while a growing number of studies have found that deforestation increases malaria prevalence in humans, suggesting that in some cases forest conservation might belong in a portfolio of anti-malarial interventions. However, previous studies of deforestation and malaria prevalence were based on a small number of countries and observations, commonly using cross-sectional analyses of less-than-ideal forest data at the aggregate jurisdictional level. In this paper we combine fourteen years of high-resolution satellite data on forest loss with individual-level data from Demographic and Health Surveys on malaria in more than 60,000 rural children in 17 countries in Africa, and fever in more than 470,000 rural children in 41 countries in Latin America, Africa, and Asia. Adhering to methods that we pre-specified in a pre-analysis plan, we tested ex-ante hypothesis based on previous literature. Using a cross-sectional regression we reject the ex-ante hypotheses that deforestation increases malaria prevalence and that intermediate levels of forest cover have highest malaria prevalence. We further reject ex ante hypotheses related to disaggregations: that the effect of deforestation on malaria is greater in Latin America and Africa than Asia, greater at earlier stages of a forest transition, greater for smaller cuts, and diminishes in effect over time. In panel regressions performed on a sub-sample of data from locations where repeated measurements were available, we also found no support for our ex ante hypotheses. And less than one-quarter of cross-sectional regressions performed on data from individual countries and years showed results consistent with our ex ante hypothesis. Because we did not find a significant effect we did not carry out initial plans to test for mediating factors, nor did we undertake a planned cost-effectiveness analysis. Our findings differ from the majority of previous empirical studies, which found that deforestation increases malaria prevalence in other contexts. We speculate that this difference may be due to an "African exception to drivers of deforestation" (Fisher, 2010) in which deforestation in Africa is largely driven by the slow expansion of subsistence or smallholder agriculture for domestic use by long-time residents in stable socio-economic settings rather than rapid clearing for market-driven agricultural exports by new frontier migrants as in Latin America and Asia. Our results imply that at least in Africa forest conservation does not appear to be an effective anti-malarial intervention. Anti-malarial efforts in Africa should focus on other proven interventions such as bed nets, indoor spraying, and housing improvements. Forest conservation efforts should focus on securing other benefits of forests, including carbon storage, biodiversity habitat, clean water provision, and other goods and services.