Low genetic diversity in a snail intermediate host (Biomphalaria pfeifferi Krass, 1848) and schistosomiasis transmission in the Senegal River Basin

Abstract

Population genetic perturbations of intermediate hosts, often a consequence of human pressure on environmental resources, can precipitate unexpectedly severe disease outbreaks. Such disturbances are set to become increasingly common following range changes concomitant with climate shifts, dwindling natural resources and major infrastructure changes such as hydroprojects. Construction of the Diama dam in the Senegal River Basin (SRB) reduced river salinity, enabling the freshwater snail intermediate host Biomphalaria pfeifferi to rapidly expand its distribution. A serious public health problem ensued, with an epidemic of intestinal schistosomiasis occurring in the previously schistosome-free Richard-Toll region within 2 years. The current study aimed to assess the population variability of B. pfeifferi in the SRB, and speculate upon its subsequent impact on host-parasite interactions following such engineered ecological change. Genetic variation at nine polymorphic microsatellite loci revealed little population differentiation in SRB snails compared with those from natural habitats in Zimbabwe, where Schistosoma mansoni transmission is much lower. 'Open' SRB habitats are associated with greater water contact, smaller population sizes and less genetic diversity, with sites downstream of Richard-Toll showing greater inter- and intrapopulation variation, concomitant with less frequent human contact. These observations may be explained by rapid expansion into pristine habitat selecting for high fecundity genotypes at the expense of schistosome resistance, presenting S. mansoni with genetically homogenous highly fecund susceptible populations around the focal point, promoting development of a highly compatible host-parasite relationship. Longitudinal study of such systems may prove important in predicting public health risks engendered by future environmental engineering projects.

Analysis of genetic diversity and population structure of Bellamya quadrata from lakes of middle and lower Yangtze River

“…We also found relatively small effective population sizes and moderate to high level of gene flow despite large separating geographic distances. Our finding is in contrast to patterns observed in many other species of freshwater snails which generally show relatively low levels of genetic diversity and strong population differentiation being often attributed to their low migration ability, high self-fertilization rates and demographic instability (Jarne 1995;Campbell et al 2010;Nguema et al 2013;Schultheiß et al 2014). The maintenance of high genetic variability and lack of population …”

“…Further anthropogenic fragmentation and demographic instability, accompanied by fluctuations of population size, should lead to elevated genetic differentiation among isolated population units. Campbell et al (2010) for example suggested that the high level of instability in snail habitats (associated with the construction of the Diama dam) may have led to a reduction of genetic diversity in Senegal. Instead of such a pattern of reduced diversity we found high genetic diversity and strong gene flow.…”

Population genetic structure ofBellamya aeruginosa(Mollusca: Gastropoda: Viviparidae) in China: weak divergence across large geographic distances

“…These findings of high genetic diversity and little differentiation is comparatively uncommon in freshwater snails in lakes due to their low migration ability, high self‐fertilization rates, and historical demographic instability (Campbell et al. 2010; Nalugwa et al. 2011; Standley et al.…”

Novel polymorphic microsatellite markers for Bellamya and their application in population genetics of three species

“…Demographic instability is generally accompanied by large fluctuations in population size and bottlenecks. Campbell et al (2010) suggested that instability of snail habitats in Senegal (associated with the construction of the Diama dam) may explain the lack of genetic diversity in those populations. The high level of genetic diversity observed for Bellamya species likely results from their wide distribution and high degree of adaptation to freshwater environments.…”