Shifting transmission risk for malaria in Africa with climate change: a framework for planning and intervention

Abstract

Background: Malaria continues to be a disease of massive burden in Africa, and the public health resources targeted at surveillance, prevention, control, and intervention comprise large outlays of expense. Malaria transmission is largely constrained by the suitability of the climate for Anopheles mosquitoes and Plasmodium parasite development. Thus, as climate changes, shifts in geographic locations suitable for transmission, and differing lengths of seasons of suitability will occur, which will require changes in the types and amounts of resources. Methods: The shifting geographic risk of malaria transmission was mapped, in context of changing seasonality (i.e. endemic to epidemic, and vice versa), and the number of people affected. A published temperature-dependent model of malaria transmission suitability was applied to continental gridded climate data for multiple future AR5 climate model projections. The resulting outcomes were aligned with programmatic needs to provide summaries at national and regional scales for the African continent. Model outcomes were combined with population projections to estimate the population at risk at three points in the future, 2030, 2050, and 2080, under two scenarios of greenhouse gas emissions (RCP4.5 and RCP8.5). Results: Estimated geographic shifts in endemic and seasonal suitability for malaria transmission were observed across all future scenarios of climate change. The worst-case regional scenario (RCP8.5) of climate change predicted an additional 75.9 million people at risk from endemic (10-12 months) exposure to malaria transmission in Eastern and Southern Africa by the year 2080, with the greatest population at risk in Eastern Africa. Despite a predominance of reduction in season length, a net gain of 51.3 million additional people is predicted be put at some level of risk in Western Africa by midcentury. Conclusions: This study provides an updated view of potential malaria geographic shifts in Africa under climate change for the more recent climate model projections (AR5), and a tool for aligning findings with programmatic needs at key scales for decision-makers. In describing shifting seasonality, it was possible to capture transitions between endemic and epidemic risk areas, to facilitate the planning for interventions aimed at year-round risk versus anticipatory surveillance and rapid response to potential outbreak locations.

Warming temperatures could expose more than 1.3 billion new people to Zika virus risk by 2050

“…In addition to this, warming in areas with higher mean temperatures is predicted to reduce suitability, as conditions pass beyond optimal transmission suitability temperatures. This can lead to reductions in predicted risk, as seen in the high-income Pacific Asia region (Table 1); this echoes findings for malaria suitability in Africa, seen in Ryan et al (2015Ryan et al ( , 2020, wherein Western Africa becomes too hot for malaria suitability, and risk appears to decline rapidly under climate change scenarios. Given the high upper thermal bounds of transmission suitability of ZIKV, other direct or indirect impacts of heat on human health are likely to arise, meaning the predicted declines at high temperatures are not necessarily an optimistic picture.…”

Impact of 1.5 oC and 2 oC global warming scenarios on malaria transmission in East Africa

“…Any climate-induced changes in temperature are likely to disproportionately affect malaria control interventions across the world (e.g. Ryan et al ., 2020 ; Siraj et al ., 2014 ). A study by ( Charlwood, 2017 ) established that An.…”

2La Paracentric Chromosomal Inversion and Overexpressed Metabolic Genes Enhance Thermotolerance and Pyrethroid Resistance in the Major Malaria Vector Anopheles gambiae

“…The increase in global mean surface temperature (GMST) of 1.5°C in the 21 st Century is projected to increase the risk of vector-borne diseases [2]. Weather and climate are among the drivers of Anopheles geographic range, intensity of transmission and seasonality of malaria, with burden of the disease projected to increase with climate change because of a greater geographic range of the Anopheles vector, shifts in phenology [3], increase in number of generations per year [4], longer season, and/or increase in the number of people at risk [5][6][7]. The population of mosquito vectors are projected to shift, but with contrasting expansions and reductions depending on the degree of local warming and the ecology of the mosquito vectors [5], leading to regionally variable patterns [2,7].…”