Change in composition of the Anopheles gambiae complex and its possible implications for the transmission of malaria and lymphatic filariasis in north-eastern Tanzania

Abstract

BackgroundA dramatic decline in the incidence of malaria due to Plasmodium falciparum infection in coastal East Africa has recently been reported to be paralleled (or even preceded) by an equally dramatic decline in malaria vector density, despite absence of organized vector control. As part of investigations into possible causes for the change in vector population density, the present study analysed the Anopheles gambiae s.l. sibling species composition in north-eastern Tanzania.MethodsThe study was in two parts. The first compared current species complex composition in freshly caught An. gambiae s.l. complex from three villages to the composition reported from previous studies carried out 2–4 decades ago in the same villages. The second took advantage of a sample of archived dried An. gambiae s.l. complex specimens collected regularly from a fourth study village since 2005. Both fresh and archived dried specimens were identified to sibling species of the An. gambiae s.l. complex by PCR. The same specimens were moreover examined for Plasmodium falciparum and Wuchereria bancrofti infection by PCR.ResultsAs in earlier studies, An. gambiae s.s., Anopheles merus and Anopheles arabiensis were identified as sibling species found in the area. However, both study parts indicated a marked change in sibling species composition over time. From being by far the most abundant in the past An. gambiae s.s. was now the most rare, whereas An. arabiensis had changed from being the most rare to the most common. P. falciparum infection was rarely detected in the examined specimens (and only in An. arabiensis) whereas W. bancrofti infection was prevalent and detected in all three sibling species.ConclusionThe study indicates that a major shift in An. gambiae s.l. sibling species composition has taken place in the study area in recent years. Combined with the earlier reported decline in overall malaria vector density, the study suggests that this decline has been most marked for An. gambiae s.s., and least for An. arabiensis, leading to current predominance of the latter. Due to differences in biology and vectorial capacity of the An. gambiae s.l. complex the change in sibling species composition will have important implications for the epidemiology and control of malaria and lymphatic filariasis in the study area.

Parallel evolution or purifying selection, not introgression, explains similarity in the pyrethroid detoxification linked GSTE4 of Anopheles gambiae and An. arabiensis

“…There is some evidence that the role of An. arabiensis in malaria transmission in the region may also be on the increase (Mawejje et al 2013) as has been seen in neighbouring countries (Lindblade et al 2006; Bayoh et al 2010; Derua et al 2012; Mwangangi et al 2013). Here, we have undertaken microarray analysis of the pyrethroid resistant phenotype in both Anopheles gambiae and An.…”

“…The relative frequency of An. arabiensis has risen in neighbouring Kenya (Lindblade et al 2006; Bayoh et al 2010; Mwangangi et al 2013) and Tanzania (Derua et al 2012) following insecticidal control measures and there is now some evidence of elevated frequencies in eastern Uganda (Mawejje et al 2013) suggesting an increasing role in malaria transmission. Resistance to pyrethroids is present, and apparently increasing, in An.…”

Pollutants and insecticides drive local adaptation in African malaria mosquitoes

“…Anopheles mosquitoes currently experience strong selective pressures across the African continent due to the increased use of pesticides/insecticides in agriculture and vector control over thelastfewdecades(WHO2012;ReidandMcKenzie2016).The idea that insecticide resistance can affect the population structure of mosquitoes as a result of a limited gene flow and/or local adaptation between resistant and sensitive populations was already evoked in the 1990s (Silvestrini et al 1998;Lenormand et al 1999). In addition to increased resistance, large-scale exposure of vector populations to insecticidetreated bed nets in Africa is also correlated with changes in species distribution and behavioral shifts (Bøgh et al 1998;Derua et al 2012;Moiroux et al 2012;Mwangangi et al 2013;Sokhna et al 2013). However, so far, despite ongoing efforts, there is no evidence that these changes can lead to genetic clustering or the creation of cryptic populations within species (e.g., Main et al 2016).…”

Phase III evaluation of the insecticidal efficacy and durability of a deltamethrin-treated polypropylene long-lasting net LifeNet®, in comparison with long-lasting nets made from polyester and polyethylene: study protocol

“…During the rainy seasons Anopheles gambiae sensu stricto and An. funestus are the most abundant malaria vectors [31]. During the dry season An.…”