Abstract
Wolbachia, a widespread bacterium which can influence mosquito-borne pathogen transmission, has recently been detected within Anopheles (An.) species that are malaria vectors in Sub-Saharan Africa. Although studies have reported Wolbachia strains in the An. gambiae complex, apparent low density and prevalence rates require confirmation. In this study, wild Anopheles mosquitoes collected from two regions of Guinea were investigated. In contrast with previous studies, RNA was extracted from adult females (n = 516) to increase the chances for the detection of actively expressed Wolbachia genes, determine Wolbachia prevalence rates and estimate relative strain densities. Molecular confirmation of mosquito species and Wolbachia multilocus sequence typing (MLST) were carried out to analyse phylogenetic relationships of mosquito hosts and newly discovered Wolbachia strains. Strains were detected in An. melas (prevalence rate of 11.6%–16/138) and hybrids between An. melas and An. gambiae sensu stricto (prevalence rate of 40.0%–6/15) from Senguelen in the Maferinyah region. Furthermore, a novel high-density strain, termed wAnsX, was found in an unclassified Anopheles species. The discovery of novel Wolbachia strains (particularly in members, and hybrids, of the An. gambiae complex) provides further candidate strains that could be used for future Wolbachia-based malaria biocontrol strategies.
Highlights
Wolbachia endosymbiotic bacteria are estimated to infect approximately 40% of insect species [1] and natural infections have been shown to have inhibitory effects on human arboviruses in mosquitoes [2,3,4]
This study provides evidence for Wolbachia strains in An. melas, a species within the An. gambiae complex, which can be an important local vector of malaria in WestAfrican coastal areas where it breeds in brackish water, mangrove forests and salt marshes [59,60]
The debate continues over the biological significance of natural strains in the An. gambiae complex, this study provides strong evidence of additional novel strains with relatively higher density infections, in addition to Wolbachia positive natural hybrids in the An. gambiae complex, and may reflect the under-reporting of natural strains in the Anopheles genus
Summary
Wolbachia endosymbiotic bacteria are estimated to infect approximately 40% of insect species [1] and natural infections have been shown to have inhibitory effects on human arboviruses in mosquitoes [2,3,4]. High-density Wolbachia strains have been used for mosquito biocontrol strategies targeting arboviruses as they induce synergistic phenotypic effects. The potential for Wolbachia to be used for biocontrol strategies targeting malaria transmission by Anopheles (An.) species has been postulated [19] and initial laboratory experiments demonstrated that transient infections in An. gambiae reduce the density of Plasmodium (P.) falciparum parasites [20]. As the majority of studies have used nested-PCR for detection, more robust evidence is required to determine whether Wolbachia strains are established as endosymbionts in Anopheles species [31]. The majority of these studies are limited to amplification of only a few genes ( 16S rRNA), and this is problematic given the possibility of amplifying prokaryotic 16S rRNA genes from non-living cells [32]. The recently discovered wAnM and wAnsA strains, found in An. moucheti and An. species A, respectively, are higher density infections that dominate the mosquito microbiome [26,33]
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