'Biomphalaria pfeifferi' (Gastropoda: Planorbidae) in Lake Malawi and Upper Shire River, Mangochi District, Malawi: Distribution, genetic diversity and pre-patent Schistosome Infections

In November 2017, 'Biomphalaria pfeifferi', the key intermediate host for 'Schistosoma mansoni' in Africa, was first reported in Lake Malawi, Mangochi District. Two subsequent malacological surveys in 2018 and 2019 confirmed its lacustrine presence, as well as its presence along the Upper Shire River. These surveys provided sufficient specimens for analyses of the genetic structure and a transmission assessment for intestinal schistosomiasis. A total of 76 collected snails were characterized by a DNA sequence analysis of a 650 bp fragment of the mitochondrial cytochrome oxidase subunit 1 (cox1); by size fractionation of six fluorescently labelled microsatellite loci (Bgmul16, Bgmul, Bpf8, rg6, U-7, and rg9); by denaturing PAGE; and by detection of pre-patent 'Schistosoma' infection by real-time PCR with a TaqMan probe. Five closely related cox1 haplotypes were identified, all present within a single location, with only one haplotype common across all the other locations sampled. No allelic size variation was detected with the microsatellites and all loci were monomorphic. Overall, the pre-patent prevalence of 'Schistosoma' spp. was 31%, with infected snails found at several sampling locations. In this part of Lake Malawi, 'Bi. Pfeifferi' exhibits low genetic diversity and is clearly being exposed to the miracidia of 'S. mansoni', which is likely facilitating the autochthonous transmission of this parasite.