Abstract:
Biomphalaria pfeifferi, a predominantly self-fertilizing freshwater snail, is the world’s most
important intermediate host for transmission of Schistosoma mansoni, one of the causative agents
of schistosomiasis, a neglected tropical disease affecting millions of people in sub-Saharan Africa.
It also sought to determine if lineages of B. pfeifferi within Asao stream persisting through different
seasons of the year, indicative of their asexual descent, could be identified. The study sought to
determine if infections by S. mansoni or other trematodes were associated with particular lineages.
Utilizing 14 microsatellite markers in a multiplex Polymerase Chain Reaction (PCR) format, a
total of 502 B. pfeifferi collected in six bi-monthly (every other month) sampling times from the
same locality in a single habitat (Asao Stream in Nyakach, Kisumu County, western Kenya) were
genotyped. Snails were isolated and screened for S. mansoni and other trematode infections. Using
the shedding method followed by microscopical examination of the cercariae found (S. mansoni,
Echinostomes, Xiphidiocercariae, Paramphistomoids, Sangunicolids and Strigeids). 26 multilocus
genotypes (MLGs) that were present at two or more sampling times were identified. Four MLGs
persisted across the entire 10-month sampling period, one of which was represented by 17
individuals. These persistent lineages harbored a variety of trematode species, with S. mansoni
being the most common. The persistent MLGs were more likely to have trematode infections than
those found only at a single sampling time. Low genetic differentiation was observed between
November and March sampling times (FST = 0.019, p = <0.05). The highest genetic differentiation
was observed between July and March sampling times (FST = 0.372, p = <0.001). Analysis of
molecular variance (AMOVA) showed higher variation among individuals within sampling times
(58%) than within individuals (33%), and a smaller variation (8%) was found among sampling
times. By identifying the presence of persistent MLGs and their associations with trematode
transmission, this study highlights the importance of considering B. pfeifferi MLGs, some of which
could be resistant to infection, when developing strategies to control schistosomiasis transmission
within Asao stream and similar ecosystems across sub-Saharan Africa.
