Date Published: February 6, 2019
Publisher: Public Library of Science
Author(s): Phong V. V. Le, Praveen Kumar, Marilyn O. Ruiz, Charles Mbogo, Ephantus J. Muturi, David Peter Keller.
The transmission of malaria is highly variable and depends on a range of climatic and anthropogenic factors. This study investigates the combined, i.e. direct and indirect, impacts of climate change on the dynamics of malaria through modifications 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 resulting from acclimation responses of vegetation under climate change. The study is performed for a rural region in Kilifi county, Kenya.
We use a stochastic lattice-based malaria (SLIM) model to make predictions of changes in Anopheles vector abundance, the life cycle of Plasmodium parasites, and thus malaria transmission under projected climate change in the study region. SLIM incorporates a nonlinear temperature-dependence of malaria parasite development to estimate the extrinsic incubation period of Plasmodium. It is also linked with a spatially distributed eco-hydrologic modeling framework to capture the impacts of climate change on soil moisture dynamics, which served as a key determinant for the formation and persistence of mosquito larval habitats on the land surface. Malaria incidence data collected from 2008 to 2013 is used for SLIM model validation. Projections of climate change and human population for the region are used to run the models for prediction scenarios.
Vegetation acclimation triggered by elevated [CO2] under climate change increases the risk of malaria. In addition, air temperature increase under climate change has opposing effects on mosquito larval habitats and the life cycles of both Anopheles vectors and Plasmodium parasites. The indirect impacts of temperature change on soil moisture dynamics are significant and should be weighed together with the direct effects of temperature change on the life cycles of mosquitoes and parasites for future malaria prediction and control.
The ecology of malaria is markedly complex, involving two different replication cycles of the Plasmodium parasite alternating in human hosts and Anopheles vectors [1, 2]. For malaria intervention, the ability to access health care and efficient vector control measures is critical to block the transmission and break the life cycle of Plasmodium. For example, the use of insecticide treated nets (ITNs) is one of the most powerful interventions that reduced malaria-related mortality from all causes among children under fives by 20% for sustained periods in Africa . Climatic factors especially air temperature and humidity play an important role in malaria transmission through influence on mosquito abundance, development, biting rate, and survival as well as parasite survival and extrinsic incubation period (EIP), the time taken by the parasites to complete their sporogonic cycles [4–6]. Therefore, climate change will likely affect the dynamics of malaria and other mosquito-borne diseases in the future [7, 8].
The elevated [CO2] condition and air temperature increase are expected to affect ecohydrological dynamics [38, 39] and nutritional quality of leaf litter that serve as food for mosquito larvae [71, 72]. Characterizing such alterations is important to understand the impacts of global warming on malaria transmission. A number of studies have shown the relationships between air temperature and precipitation changes on the dynamics of malaria [17–23]. In this work, our model incorporating the acclimatory mechanisms of vegetation under climate change is used to predict the transmission dynamics of malaria. Model results indicate the opposing effects of elevated [CO2] and air temperature increase on the dynamics of malaria. Given the complexity of malaria transmission under environmental disturbances, these effects would play an important role to better understand how malaria will be likely altered under climate change, thus contributing to the intervention of this disease.