BackgroundIntestinal schistosomiasis was confirmed endemic in Mangochi District, Malawi,
in May of 2018 following an unexpected encounter with discreet populations of Biomphalaria
spp. freshwater snails during routine malacological surveillance activities. Since
then, only limited malacological surveillance of Biomphalaria has been carried out,
and so the distribution of Biomphalaria populations in this area is currently unclear.
Additionally, sites of active Schistosoma mansoni transmission in this area are also
unknown. In the present study, through extensive malacological surveillance, we aimed
to formally document the distribution of Biomphalaria in Mangochi District. We also
aimed to identify active intestinal schistosomiasis transmission sites in this area
through subjecting all collected Biomphalaria to a recently developed S. mansoni-specific
molecular xenomonitoring PCR.MethodsThree malacological surveys were carried out along
the southern shoreline of Lake Malawi, Mangochi District, Malawi, in November 2021,
July 2022 and October/November 2022. All collected Biomphalaria were subjected to
cercarial shedding analysis to identify active Schistosoma infections. Shed cercariae
were then genotyped to species level using a standard multi-locus PCR and Sanger sequencing
protocol. Following this, a subset of Biomphalaria from each collection site were
also genotyped to species level using a standard PCR and Sanger sequencing protocol.
All collected Biomphalaria were then subjected to a recently developed S. mansoni-specific
molecular xenomonitoring PCR to identify infected, but non-shedding, Biomphalaria.ResultsA
total of 589 Biomphalaria were collected across all three surveys. One single Biomphalaria
(0.17%) specimen was found to be actively shedding Schistosoma cercariae, which were
molecularly confirmed as S. mansoni. All genotyped Biomphalaria (n = 42) were molecularly
identified as B. pfeifferi. A further 19 Biomphalaria specimens, collected from four
different surveillance sites, were found to be infected with S. mansoni through molecular
xenomonitoring. Intestinal schistosomiasis transmission was therefore identified at
four different foci in Mangochi District.ConclusionsOur study highlights the importance
of molecular approaches to investigate Biomphalaria populations and monitor Biomphalaria-associated
intestinal schistosomiasis transmission in endemic areas. As such, the continued development
and use of such approaches, in particular the development and use of molecular xenomonitoring
assays that can be carried out in resource-poor schistosomiasis-endemic settings,
is encouraged. The revision of ongoing schistosomiasis control programmes in Mangochi
District, in line with WHO recommendations, is also encouraged.
