Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing

Abstract

Deforestation and land use change are among the most pressing anthropogenic environmental impacts. In Brazil, a resurgence of malaria in recent decades paralleled rapid deforestation and settlement in the Amazon basin, yet evidence of a deforestation-driven increase in malaria remains equivocal. We hypothesize an underlying cause of this ambiguity is that deforestation and malaria influence each other in bidirectional causal relationships—deforestation increases malaria through ecological mechanisms and malaria reduces deforestation through socioeconomic mechanisms—and that the strength of these relationships depends on the stage of land use transformation. We test these hypotheses with a large geospatial dataset encompassing 795 municipalities across 13 y (2003 to 2015) and show deforestation has a strong positive effect on malaria incidence. Our results suggest a 10% increase in deforestation leads to a 3.3% increase in malaria incidence (∼9,980 additional cases associated with 1,567 additional km2 lost in 2008, the study midpoint, Amazon-wide). The effect is larger in the interior and absent in outer Amazonian states 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 behavior or economic development. We estimate a 1% increase in malaria incidence results in a 1.4% decrease in forest area cleared (∼219 fewer km2 cleared associated with 3,024 additional cases in 2008). This bidirectional socioecological feedback between deforestation and malaria, which attenuates as land use intensifies, illustrates the intimate ties between environmental change and human health.

Impact of prior and projected climate change on US Lyme disease incidence

“…More generally, our results are consistent with expectations from vector thermal biology that suggest that warming temperatures generally increase transmission near the cold edge of a vector's range limit, but may decrease or have variable effects elsewhere (Martens et al 1995, Ogden and Lindsay 2016, Lafferty and Mordecai 2016, Mordecai et al 2019. For tick-borne diseases, as for other vector-borne diseases, multiple temperature-sensitive traits combine to influence transmission, including survival, development rates, and host-seeking (Randolph et al 2002, Ogden et al 2004, Randolph 2004, Ogden and Lindsay 2016, Ogden 2017.…”

“…We used a least squares dummy variable (termed "fixed-effects" in econometrics) regression approach to estimate changes in Lyme disease incidence using repeated observations of the same groups (counties) from 2000 -2017 (Larsen et al 2019). This class of statistical approaches has been developed to isolate potential causal relationships in the absence of randomized experiments where such experiments are not feasible (Larsen et al 2019, MacDonald andMordecai 2019). We included 'county' and 'year' dummy variables to control for any unobserved heterogeneity that may influence reported Lyme disease incidence in a particular county across all years (e.g., geographic features, number of health care providers), or influence Lyme disease in all counties in a given year (e.g., changes in disease case definition), respectively.…”

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

“…Importantly, deforestation was never associated with lower risks of P. vivax. A recent study in the Amazon [43] reported a similar attenuation of the effects of deforestation on P. vivax compared to P. falciparum, most likely because of P. vivax parasites' ability to relapse months or even years after infection, which decouples the association between transmission and incidence data. These species-specific differences may also explain why the pattern of spatio-temporal associations between malaria and deforestation were markedly clearer in the south than in the north where P. vivax dominates.…”

Conservation in the maelstrom of Covid‐19 – a call to action to solve the challenges, exploit opportunities and prepare for the next pandemic

“…In the longer term, austerity measures that are likely to be introduced once Covid‐19 is under control are bound to further reduce investment in conservation agencies and conservation research. The glaring paradox with these financial constraints is that intact functioning ecosystems, with low rates of conversion from natural habitats, are critical for delivering ecosystem services including regulating zoonotic disease outbreaks and providing other health benefits (Cunningham et al ., 2017; Faust et al ., 2018; MacDonald & Mordecai, 2019). Conservationists must make the health and well‐being benefits of the natural world increasingly clear and advocate that responses to the current crisis must have minimal impact on longer‐term disease risks associated with environmental destruction.…”

“…While there is a risk of a resurgent black‐market in wildlife trade, as happened when a ban was attempted in 2003 in response to the SARS outbreak, 10 there are clear opportunities for reforming wildlife trade and easing pressure on wild populations. There is a more general notable opportunity for public education on the links between key pressures on biodiversity, such as deforestation and wildlife trade and consumption, and the risk of pandemics (Cunningham et al ., 2017; Faust et al ., 2018; MacDonald & Mordecai, 2019). Such education programmes combined with people’s personal experience of the severe adverse impacts of pandemics could be a powerful force in lobbying decision‐makers to enhance environmental protection.…”