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 14 years of high-resolution satellite data on forest loss with individual-level survey data 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 hypotheses derived from previous literature. We did not find that deforestation increased malaria prevalence nor that intermediate levels of forest cover had higher malaria prevalence. Our findings differ from most previous empirical studies, which found deforestation to be associated with greater malaria prevalence in other contexts. We speculate that this difference may be because deforestation in Africa is largely driven by the slow expansion of subsistence or smallholder agriculture for domestic use by long-time residents in stable socioeconomic settings rather than by 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 anti-malarial efforts should focus on other proven interventions such as bed nets, 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.

Spatio-temporal associations between deforestation and malaria incidence in Lao PDR

“…The importance of addressing complex confounding structures influencing the relationship between deforestation and malaria was also highlighted by Bauhoff and Busch, 2020 . Variables such as temperature ( Beck-Johnson et al, 2013 ; Mordecai et al, 2013 ), precipitation ( Parham and Michael, 2010 ; Parham et al, 2012 ), or seasonality Hay et al, 1998 are known environmental predictors of malaria, although the spatio-temporal scale of those effects often varies across different areas ( Teklehaimanot et al, 2004 ).…”

“… Bauhoff and Busch, 2020 identified only 10 empirical studies that assessed the relationship between deforestation and malaria with appropriate adjustments for confounding. Of these, seven reported a positive association ( Austin et al, 2017 ; Wayant et al, 2010 ; Olson et al, 2010 ; Terrazas et al, 2015 ; Pattanayak et al, 2010 ; Garg, 2015 ; Fornace et al, 2016 ), two did not find any associations ( Bauhoff and Busch, 2020 ; Hahn et al, 2014a ), and one disputed study found a negative association ( Valle and Clark, 2013 ; Hahn et al, 2014b ; Valle, 2014 ). Most recently, a study found deforestation to increase malaria risk and malaria to decrease deforestation activities in the Amazon, using an instrumental variable analysis to disentangle any reverse causality loop ( MacDonald and Mordecai, 2019 ).…”

Amphibian Collapses Exacerbated Malaria Outbreaks in Central America

“…Deforestation in particular has received increased attention in recent years and is hypothesized to operate through changes to the physical environment, malarial mosquito biology, and human exposure (15). While most have found that deforestation is associated with increased malaria incidence (16), this result does not hold across all regions and study designs (17). However, linkages between malarial dynamics and ecosystem disruption by invasive species has not been previously studied, aside from well-known linkages to invasive mosquito vectors.…”

Spatio-temporal associations between deforestation and malaria incidence in Lao PDR

“…The importance of addressing complex confounding structures influencing the relationship between deforestation and malaria was highlighted by Bauhoff et al [12]. Variables such as temperature [13, 44], precipitation [51, 50] or seasonality [35] are known environmental predictors of malaria, although the spatio-temporal scale of those effects if often highly variable across different areas [59].…”

“…Bauhoff et al [12] identified only 10 empirical studies that assessed the relationship between deforestation and malaria with appropriate adjustments for confounding. Of these, seven reported a positive association [10, 67, 48, 60, 53, 27, 25], two did not find any associations [12, 31], and one disputed study found a negative association [64, 32, 63]. Most recently, a study found deforestation to increase malaria risk and malaria to decrease deforestation activities in the Amazon, using an instrumental variable analysis to disentangle any reverse causality loop [43].…”