Habitat suitability and ecological niche profile of major malaria vectors in Cameroon

Abstract

Background: Suitability of environmental conditions determines a species distribution in space and time. Understanding and modelling the ecological niche of mosquito disease vectors can, therefore, be a powerful predictor of the risk of exposure to the pathogens they transmit. In Africa, five anophelines are responsible for over 95% of total malaria transmission. However, detailed knowledge of the geographic distribution and ecological requirements of these species is to date still inadequate.

Methods: Indoor-resting mosquitoes were sampled from 386 villages covering the full range of ecological settings available in Cameroon, Central Africa. Using a predictive species distribution modeling approach based only on presence records, habitat suitability maps were constructed for the five major malaria vectors Anopheles gambiae, Anopheles funestus, Anopheles arabiensis, Anopheles nili and Anopheles moucheti. The influence of 17 climatic, topographic, and land use variables on mosquito geographic distribution was assessed by multivariate regression and ordination techniques.

Results: Twenty-four anopheline species were collected, of which 17 are known to transmit malaria in Africa. Ecological Niche Factor Analysis, Habitat Suitability modeling and Canonical Correspondence Analysis revealed marked differences among the five major malaria vector species, both in terms of ecological requirements and niche breadth. Eco-geographical variables (EGVs) related to human activity had the highest impact on habitat suitability for the five major malaria vectors, with areas of low population density being of marginal or unsuitable habitat quality. Sunlight exposure, rainfall, evapo-transpiration, relative humidity, and wind speed were among the most discriminative EGVs separating "forest" from "savanna" species.

Conclusions: The distribution of major malaria vectors in Cameroon is strongly affected by the impact of humans on the environment, with variables related to proximity to human settings being among the best predictors of habitat suitability. The ecologically more tolerant species An. gambiae and An. funestus were recorded in a wide range of eco-climatic settings. The other three major vectors, An. arabiensis, An. moucheti, and An. nili, were more specialized. Ecological niche and species distribution modelling should help improve malaria vector control interventions by targeting places and times where the impact on vector populations and disease transmission can be optimized.

Figure 1

Topographic map of Cameroon. Localities sampled for the mosquito domestic fauna are shown as dark dots (N = 386) among all the recorded populated places present across Cameroon shown as gray dots (N = 10,700). Dotted lines delimit the main bio-geographic domains [31].

Figure 2

Habitat suitability maps for the five major malaria vectors in Cameroon. Dots represent species presence points used for the ENFA: (A) An. gambiae; (B) An. funestus; (C) An. arabiensis; (D) An. moucheti and (E) An. nili. Different colours identify the four classes of habitat quality.

Figure 3

Coefficients of the discriminant function differentiating the ecological niche of pairs of major malaria vectors based on 17 eco-geographical variables.

Figure 4

Ordination biplot diagram showing the dispersion of ten malaria vectors and 14 eco-geographical variables on the first two canonical axes of a Canonical Correspondence Analysis. Crosses represent the average niche centroid for each mosquito species. In brackets the EGV contribution to total species variance, and the total species variance explained by each canonical axis.