Behavioural plasticity of Anopheles coluzzii and Anopheles arabiensis undermines LLIN community protective effect in a Sudanese-savannah village in Burkina Faso

Abstract

Background: Despite the overall major impact of Long Lasting Insecticide treated Nets (LLINs) in eliciting individual and collective protection to malaria infections, some sub-Saharan Countries, including Burkina Faso, still carry a disproportionately high share of the global malaria burden. This study aims to analyse the possible entomological bases of LLIN limited impact, focusing on a LLIN-protected village in the Plateau Central region of Burkina Faso. Methods: Human Landing Catches (HLCs) were carried out in 2015 both indoors and outdoors at different time-windows during the highest biting activity phase for Anopheles gambiae s.l. Collected specimens were morphologically and molecularly identified and processed for Plasmodium detection and L1014F insecticide-resistance allele genotyping. Results: Almost 2.000 unfed An. gambiae s.l. (54% Anopheles coluzzii , 44% Anopheles arabiensis ) females landing on human volunteers were collected, corresponding to a median number of 23.5 females/person/hour. No significant differences are observed in median numbers of mosquitoes collected indoor and outdoor, nor between sporozoite rates in An. coluzzii (6.1%) and An. arabiensis (5.5%). The estimated median hourly Entomological Inoculation Rate (EIR) on volunteers is 1.4 infective bites/person/hour. Results do not show evidence of the biting peak during night hours typical for An. gambiae s.l. in the absence of bednet protection. The frequency of L1014F resistant allele (N=285) was 66% in An. coluzzii and 38% in An. arabiensis . Conclusions: The observed biting rate and sporozoite rates are in line with the literature data available for An. gambiae s.l . in the same geographical area before LLIN implementation and highlight high levels of malaria transmission in the study village. Homogeneous biting rate throughout the night and lack of preference for indoor-biting activity suggest the capacity of both An. coluzzii and An. arabiensis to adjust their host-seeking behaviour to bite humans despite bednet protection, accounting for the maintenance of high rates of mosquito infectivity and malaria transmission. These results – despite being limited to a local situation in Burkina Faso – represent a paradigmatic example of how high densities and behavioural plasticity in the vector population may contribute to explain the limited impact of LLINs on malaria transmission in holo-endemic Sudanese savannah areas in West Africa.

Uncovering transposable element variants and their potential adaptive impact in urban populations of the malaria vectorAnopheles coluzzii

“…coluzzii evolution across the continent (6, 7). The adaptive flexibility of this mosquito has been also highlighted by its rapid competence to expand its range of peak biting times in order to avoid insecticide treated bed-nets (8). This extraordinary adaptative capacity makes this malaria vector a threat for malaria control.…”

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“…Field studies in East Africa have reported increased zoophagy [23,24,28], feeding outdoors or early evening biting [29] and changes in resting behaviour from indoor to outdoor [28,30,31]. These behavioural changes might have been due to selection pressure from increased coverage of LLINs [32][33][34][35]. The scale-up of LLINs in Africa has been associated with a species shift from the highly endophilic An.…”