NaturalWolbachiainfections are common in the major malaria vectors in Central Africa

Abstract

During the last decade, the endosymbiont bacterium Wolbachia has emerged as a biological tool for vector disease control. However, for long time, it was believed that Wolbachia was absent in natural populations of Anopheles. The recent discovery that species within the Anopheles gambiae complex hosts Wolbachia in natural conditions has opened new opportunities for malaria control research in Africa. Here, we investigated the prevalence and diversity of Wolbachia infection in 25 African Anopheles species in Gabon (Central Africa). Our results revealed the presence of Wolbachia in 16 of these species, including the major malaria vectors in this area. The infection prevalence varied greatly among species, confirming that sample size is a key factor to detect the infection. Moreover, our sequencing and phylogenetic analyses showed the important diversity of Wolbachia strains that infect Anopheles. Co-evolutionary analysis unveiled patterns of Wolbachia transmission within Anopheles species, suggesting that past independent acquisition events were followed by co-cladogenesis. The large diversity of Wolbachia strains that infect natural populations of Anopheles offers a promising opportunity to select suitable phenotypes for suppressing Plasmodium transmission and/or manipulating Anopheles reproduction, which in turn could be used to reduce the malaria burden in Africa.

An elusive endosymbiont: DoesWolbachiaoccur naturally inAedes aegypti?

“…Similar to Ae. aegypti, Anopheles mosquitoes (which transmit Plasmodium parasites that cause malaria) were also thought to be uninfected by Wolbachia, though several recent studies have detected Wolbachia in this genus (Baldini et al, 2014, Jeffries et al, 2018, Ayala et al, 2019. In a critical analysis of studies in Anopheles gambiae, Chrostek and Gerth (2019) assert that the evidence is currently insufficient to diagnose natural infections in this species.…”

Is Anopheles gambiae a natural host of Wolbachia?

“…The protocol was used in several subsequent studies (29–31), but proved unreliable, as Gomes et al reported 19% of the technical replicates yielding discordant results, even when total number of cycles was increased to 80 (29). At the same time, the wSpec amplification protocol was sensitive enough to detect Wolbachia in a filarial nematode residing within one of the Anopheles coustani guts (30). Thus, this diagnostic test can detect Wolbachia in organisms interacting with Anophele s.…”

“…the transposases with the highest coverage in genomic data) were never tested on Wolbachia sequences found in Anopheles (38, 39). Amplification of other Wolbachia sequences from putatively infected mosquitos, including Wolbachia surface protein and MLST genes, has also been challenging (26, 27, 29–31), requiring protocol modifications (30) or the use of more than one mosquito sample (31), and was unsuccessful in some cases (26, 27). Overall, detection of Wolbachia sequences in A. gambiae by PCR-based methods remains challenging.…”

“…This contamination could come from several sources. First, ectoparasitic mites or midges, and endoparasitic nematodes in Anopheles could contaminate whole tissue DNA extracts, as shown by the detection of the Wolbachia symbiont of Dirofilaria immitis in Anopheles coustani DNA preparation (30). However, the presence of unknown symbionts or parasites with novel Wolbachia strains is very challenging to test for.…”

Complete mitogenome sequence of Anopheles coustani from São Tomé island

“…The 672 bp long COI fragment spanning 1464-2135 of the A. coustani Mt is highly similar to the COI fragment sequences of A. coustani from Mali (Huestis et al 2019), Guinea-Bissau (Gordicho et al 2014) and Kenya (St Laurent et al 2016) with an average pairwise identity of 99.4% (±0.2 SD). The 622 bp long COII fragment spanning Mt:3054-3675 was 99.7% identical to the published A. coustani COII sequence from Gabon (Ayala et al 2019). In addition, we sequenced the internal transcribed spacer 2 (ITS2; GenBank: MT791041) region of nuclear ribosomal DNA which was 99.64% identical to the published A. coustani from Guinea (Cansado-Utrilla et al 2020).…”