Zoom in at African country level: potential climate induced changes in areas of suitability for survival of malaria vectors

Abstract

Background: Predicting anopheles vectors' population densities and boundary shifts is crucial in preparing for malaria risks and unanticipated outbreaks. Although shifts in the distribution and boundaries of the major malaria vectors (Anopheles gambiae s.s. and An. arabiensis) across Africa have been predicted, quantified areas of absolute change in zone of suitability for their survival have not been defined. In this study, we have quantified areas of absolute change conducive for the establishment and survival of these vectors, per African country, under two climate change scenarios and based on our findings, highlight practical measures for effective malaria control in the face of changing climatic patterns.

Methods: We developed a model using CLIMEX simulation platform to estimate the potential geographical distribution and seasonal abundance of these malaria vectors in relation to climatic factors (temperature, rainfall and relative humidity). The model yielded an eco-climatic index (EI) describing the total favourable geographical locations for the species. The EI values were classified and exported to a GIS package. Using ArcGIS, the EI shape points were clipped to the extent of Africa and then converted to a raster layer using Inverse Distance Weighted (IDW) interpolation method. Generated maps were then transformed into polygon-based geo-referenced data set and their areas computed and expressed in square kilometers (km(2)).

Results: Five classes of EI were derived indicating the level of survivorship of these malaria vectors. The proportion of areas increasing or decreasing in level of survival of these malaria vectors will be more pronounced in eastern and southern African countries than those in western Africa. Angola, Ethiopia, Kenya, Mozambique, Tanzania, South Africa and Zambia appear most likely to be affected in terms of absolute change of malaria vectors suitability zones under the selected climate change scenarios.

Conclusion: The potential shifts of these malaria vectors have implications for human exposure to malaria, as recrudescence of the disease is likely to be recorded in several new areas and regions. Therefore, the need to develop, compile and share malaria preventive measures, which can be adapted to different climatic scenarios, remains crucial.

Figure 1

Range shifts in the distribution of Anopheles gambiae (A, B, C) and An. arabiensis (D, E, F) using the Eco-climatic indices (EI). Indices reclassified from the original data by Tonnang et al.[14]; (A, D), Eco-climatic indices for current climate; (B, E) and (C, F) correspond to climate change scenario 1 and 2 respectively.

Figure 2

Bar charts showing the absolute change in area (km²) that may occur due to possible change in climate for Anopheles gambiae per African country. Values obtained by subtracting the Eco-climatic index (EI) estimates of projected scenarios 1 (A) and 2 (B) criteria to the EI estimates obtained under current climate for each country. The height of a bar shows the proportion of area in a scale of (A) 150,000 km² and (B) 130,000 km²; bar display on the positive axis represents an increasing area and a reverse bar in the negative axis, a decreasing area.

Figure 3

Bar charts showing the absolute change in areas (km²) that may occur due to possible change in climate for Anopheles arabiensis per African country. Values obtained by subtracting the Eco-climatic index (EI) estimates of projected scenarios 1 (A) and 2 (B) criteria to the EI estimates obtained under current climate for each country. The height of a bar shows the proportion of area in a scale of (A) 150,000 km² and (B) 130,000 km²; bar display on the positive axis represents an increasing area and a reverse bar in the negative axis, a decreasing area.