Composition and genetics of malaria vector populations in the Central African Republic

Abstract

Background: In many African countries malaria has declined sharply due to a synergy of actions marked by the introduction of vector control strategies, but the disease remains a leading cause of morbidity and mortality in Central African Republic (CAR). An entomological study was initiated with the aim to characterize the malaria vectors in Bangui, the capital of CAR, and determine their vector competence.

Methods: A cross-sectional entomological study was conducted in 15 sites of the district of Bangui, the capital of CAR, in September-October 2013 and a second collection was done in four of those sites between November and December 2013. Mosquitoes were collected by human landing catch (HLC) indoors and outdoors and by pyrethrum spray catch of indoor-resting mosquitoes. Mosquitoes were analysed for species and multiple other attributes, including the presence of Plasmodium falciparum circumsporozoite protein or DNA, blood meal source, 2La inversion karyotype, and the L1014F kdr insecticide resistance mutation.

Results: Overall, 1292 anophelines were analysed, revealing a predominance of Anopheles gambiae and Anopheles funestus, with a small fraction of Anopheles coluzzii. Molecular typing of the An. gambiae complex species showed that An. gambiae was predominant (95.7 %) as compared to An. coluzzii (2.1 %), and Anopheles arabiensis was not present. In some areas the involvement of secondary vectors, such as Anopheles coustani, expands the risk of infection. By HLC sampling, An. funestus displayed a stronger endophilic preference than mosquitoes from the An. gambiae sister taxa, with a mean indoor-capture rate of 54.3 % and 67.58 % for An. gambiae sister taxa and An. funestus, respectively. Human biting rates were measured overall for each of the species with 28 or 29 bites/person/night, respectively. Both vectors displayed a strong human feeding preference as determined by blood meal source, which was not different between the different sampling sites. An. coustani appears to be highly exophilic, with 92 % of HLC samples captured outdoors. The mean CSP rate in head-thorax sections of all Anopheles was 5.09 %, and was higher in An. gambiae s.l. (7.4 %) than in An. funestus (3.3 %). CSP-positive An. coustani were also detected in outdoor HLC samples. In the mosquitoes of the An. gambiae sister taxa the kdr-w mutant allele was nearly fixed, with 92.3 % resistant homozygotes, and no susceptible homozygotes detected.

Conclusions: This study collected data on anopheline populations in CAR, behaviour of vectors and transmission levels. Further studies should investigate the biting behaviour and susceptibility status of the anophelines to different insecticides to allow the establishment of appropriate vector control based on practical entomological knowledge.

Keywords: Anopheles; Bangui; Central African Republic; Insecticide resistance; Malaria.

Fig. 1

Number of bites per person per night of Anopheles funestus and mosquitoes belonging to the Anopheles gambiae sister taxa (September–October 2013). Mosquitoes (n = 825) were collected by HLC in 15 districts of Bangui

Fig. 2

Hourly aggressiveness of Anopheles funestus and Anopheles gambiae sister taxa populations (n = 825) collected by HLC in September–October 2013 (% and 95 % confidence intervals). a Global result from the 15 districts, b from Gbanikola, c from Ile de singe and d from Taoka St. Paul

Fig. 3

Human blood index (proportion and 95 % confidence interval) in 149 mosquitoes from Anopheles gambiae sister taxa (September–October 2013). Mosquitoes were collected by PSC in 15 districts of Bangui

Fig. 4

Relation between 2L chromosomal forms, Plasmodium parasite detection and place of capture (November–December 2013). Anopheles gambiae sister taxa (n = 183) were collected indoors and outdoors by HLC and PSC in four districts of Bangui