Range dynamics of Anopheles mosquitoes in Africa suggest a significant increase in the malaria transmission risk

Abstract

Despite a more than 100-year effort to combat malaria, it remains one of the most malignant infectious diseases globally, especially in Africa. Malaria is transmitted by several Anopheles mosquitoes. However, until now few studies have investigated future range dynamics of major An. mosquitoes in Africa through a unified scheme. Through a unified scheme, we developed 21 species distribution models to predict the range dynamics of 21 major An. species in Africa under future scenarios and also examined their overall range dynamic patterns mainly through suitability overlap index and range overlap index. Although future range dynamics varied substantially among the 21 An. species, we predicted large future range expansions for all 21 An. species, and increases in suitability overlap index were detected in more than 90% of the African continent for all future scenarios. Additionally, we predicted high range overlap index in West Africa, East Africa, South Sudan, Angola, and the Democratic Republic of the Congo under future scenarios. Although the relative impacts of land use, topography and climate variables on the range dynamics depended on species and spatial scale, climate played the strongest roles in the range dynamics of most species. Africa might face an increasing risk of malaria transmissions in the future, and better strategies are required to address this problem. Mitigating climate change and human disturbance of natural ecosystems might be essential to reduce the proliferation of An. species and the risk of malaria transmissions in Africa in the future. Our strategies against their impacts should be species-specific.

Keywords: Africa; Anopheles species; future scenarios; malaria transmission; range dynamics.

FIGURE 1

Occurrences of 21 Anopheles species in Africa. Records were compiled from the Global Biodiversity Information Facility (GBIF) and a published compendium by Kyalo et al. (2016). There was a total of 22,716 occurrence records after spatial rarefication.

FIGURE 2

Importance of the predictors in the species distribution models. Topographic, climatic and human disturbance predictors were in green, blue and yellow, respectively. We min‐max standardized the importance values of the predictors for each species, separately. The blanks indicated that predictors were not in our final and formal models.

FIGURE 3

Suitability overlap indices of 21 Anopheles species in Africa. (a) Current conditions; (b) F126 scenario; (c) F585 scenario; (d) M126 scenario; (e) M585 scenario. Under all scenarios, high suitability overlap indices were mainly detected in the regions with latitude from equator to 15 north latitude degree in Africa, and it was also identified in Tanzania, Mozambique, Swaziland and Madagascar.

FIGURE 4

Changes in suitability overlap index of 21 Anopheles species under current‐future scenarios in Africa. (a) Current‐F126; (b) current‐F585; (c) current‐M126; (d) current‐M585. Substantial increases in suitability overlap indices were mainly projected in the southern part of West Africa, the southeastern part of Africa and Central Africa. Under the current‐F585 and current‐M585 scenarios, substantial increases in suitability overlap indices were primarily detected in the southeastern part of Africa, Central Africa and the scattered regions in southern part of West Africa.

FIGURE 5

Range overlap indices of 21 Anopheles species. (a) Range overlap indices under current conditions; (b) range overlap indices under F126 scenario; (c) range overlap indices under F585 scenario; (d) range overlap indices under M126 scenario; (e) range overlap indices under M585 scenario. Under all scenarios, high range overlap indices were detected in West Africa and East Africa, South Sudan, Angola and Democratic Republic Congo.

FIGURE 6

Overlapped expanding, stabilizing and unfilling ranges of 21 Anopheles species under current‐future scenarios. (a) Expanding range overlap index under current‐F126 scenarios; (b) stabilizing range overlap index under current‐F126 scenarios; (c) unfilling range overlap index under current‐F126 scenarios; (d) expanding range overlap index under current‐F585 scenarios; (e) stabilizing range overlap index under current‐F585 scenarios; (f) unfilling range overlap index under current‐F585 scenarios; (g) expanding range overlap index under current‐M126 scenarios; (h) stabilizing range overlap index under current‐M126 scenarios; (i) unfilling range overlap index under current‐M126 scenarios; (j) expanding range overlap index under current‐M585 scenarios; (k) stabilizing range overlap index under current‐M585 scenarios; (l) unfilling range overlap index under current‐M585 scenarios.