The transmission of malaria is highly variable and depends on a range of climatic and anthropogenic factors. For more than two decades, there has been a growing concern and hot debate over the impact of global warming on this deadly mosquito-borne disease. It is now widely recognized that while malaria risk could be limited by economic growth, changes in climate suitability in poor regions remain a significant challenge for malaria control.

The ecology of malaria is markedly complex, involving two different replication cycles of the Plasmodium parasite alternating in human hosts and Anopheles vectors (Fig. 1). These cycles are often controlled by fluctuations dominated by the random nature of population events and the space-time variability of environmental conditions. While 3/4 of the mosquitoes’ life stages are aquatic, the life cycle of Plasmodium inside the mosquitoes, that are ectothermic or cold-blooded insects, is air-temperature dependent. So, it is very likely that ecohydrological shifts in response to global warming will have a significant impact on the dynamics of malaria.

We investigated the complexity and ecological aspects of climate change’s impacts on malaria transmission. Specifically, we analyzed modification in (i) the sporogonic cycle of Plasmodium induced by air temperature increase, and (ii) the life cycle of Anopheles vector triggered by changes in natural breeding habitat arising from the altered moisture dynamics. We developed a stochastic modeling approach to capture uncertainty and the interaction between malaria dynamics and the life cycles of both vectors and parasites. Our model consists of two stochastic time-continuous, space- discrete models: one for vector dispersal that represents the entomological life cycles of female Anopheles, and a second for malaria dynamics that simulates the circulation of the Plasmodium pathogen between host and vector populations. We also coupled this framework with a sophisticated ecohydrologic model to incorporate climate-driven hydrologic and ecologic processes as factors that determine mosquito population and malaria transmission dynamics. Our study was performed in a coastal area in Kenya.

This research revealed for the first time the complicated role of vegetation acclimation under climate change on malaria and indicated an indirect but often ignored impact of air temperature increase on malaria transmission through reduction in breeding habitats and vector density. Particularly, we showed that elevated atmospheric CO₂ concentration increases the habitat availability for mosquito reproduction, which leads to higher density of vectors and an increase in malaria incidence. Unlike the elevated CO₂ condition, the increase of air temperature has two distinct effects on malaria dynamics. First, higher air temperature shortens the life cycles of Anopheles and Plasmodium. Second, it also reduces soil moisture, thus decreasing the habitat availability for the vector. Our findings shed light on better understanding the linkage between climate change and the infection dynamics of malaria.

Phong V. V. Le ^1,2, Praveen Kumar ^1
1Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL, USA
²Faculty of Hydrology Meteorology and Oceanography, Vietnam National University, Hanoi, Vietnam

Publications

Predicting the direct and indirect impacts of climate change on malaria in coastal Kenya.
Le PVV, Kumar P, Ruiz MO, Mbogo C, Muturi EJ
PLoS One. 2019 Feb 6

Stochastic lattice-based modelling of malaria dynamics.
Le PVV, Kumar P, Ruiz MO
Malar J. 2018 Jul 5