Molecular epidemiology ofSchistosoma mansoniin Uganda: DNA barcoding reveals substantial genetic diversity within Lake Albert and Lake Victoria populations

Abstract

Representative samples of Ugandan Schistosoma mansoni from Lake Albert and Lake Victoria were examined using DNA barcoding, sequence analysis of two partially overlapping regions - ASMIT (396 bp) & MORGAN (617 bp) - of the mitochondrial cytochrome oxidase subunit I (cox1). The Victorian sample exhibited greater nucleotide diversity, 1.4% vs. 1.0%, and a significant population partition appeared as barcodes did not cross-over between lakes. With one exception, Lake Albert populations were more mixed by sampled location, while those from Lake Victoria appeared more secluded. Using statistical parsimony, barcode ASMIT 1 was putatively ancestral to all others and analysis of MORGAN cox1 confirmed population diversity. All samples fell into two of five well-resolved lineages; sub-lineages therein broadly partitioning by lake. It seems that barcode ASMIT 1 (and close variants) was likely widely dispersed throughout the Nilotic environment but later diversified in situ, and in parallel, within Lake Albert and Lake Victoria. The genetic uniformity of Ugandan S. mansoni can no longer be assumed, which might better explain known epidemiological heterogeneities. While it appears plausible that locally evolved heritable traits could spread through most of the Lake Albert populations, it seems unlikely they could quickly homogenise into Lake Victoria or amongst populations therein.

Genetic Consequences of Mass Human Chemotherapy for Schistosoma mansoni: Population Structure Pre- and Post-Praziquantel Treatment in Tanzania

“…The unpredicted apparent "bottleneck" imposed by one round of MDA on schistosome population genetics has several putative explanations, all of which require further investigation. It may indicate that not all parasites present in r efugia at the time of treatment contribute to the re-infection of children in this age group (7)(8)(9)(10)(11), and hence the "effective reservoir" may be smaller than previously thought. One could speculate that parasite genetic differentiation may occur between human hosts of different ages caused by immunological differences, with the untreated pre-school children, teenagers, and adults not treated in this study harboring different parasite genotypes, which may be less likely to re-infect children in the study group ages (7)(8)(9)(10)(11).…”

“…It may indicate that not all parasites present in r efugia at the time of treatment contribute to the re-infection of children in this age group (7)(8)(9)(10)(11), and hence the "effective reservoir" may be smaller than previously thought. One could speculate that parasite genetic differentiation may occur between human hosts of different ages caused by immunological differences, with the untreated pre-school children, teenagers, and adults not treated in this study harboring different parasite genotypes, which may be less likely to re-infect children in the study group ages (7)(8)(9)(10)(11). This reduction in genetic diversity as a result of one MDA treatment may therefore result from a large number of the genotypes of parasites currently adapted to infecting humans of the group 7-11 years of age having been killed by chemotherapy, with not all parasites present in the "reservoir" adapted to re-infect these children or being present in the specific transmission foci that these children frequent.…”

“…Although only a few population genetic studies have been performed on schistosomes to date, they have identified significant genetic diversity in adult worms within both human and rodent hosts. [7][8][9][10][11] There is currently no effective vaccine against schistosomiasis and interruption of the transmission cycle through mollusciciding, biological control of the intermediate snail hosts and health education have generally proved insufficient control methods on their own. 2 Chemotherapy with praziquantel (PZQ) is therefore the mainstay for schistosomiasis control 12 and PZQ will remain the only drug of choice for several years.…”

Genetic differentiation of cercariae infrapopulations of the avian schistosome Trichobilharzia szidati based on RAPD markers and mitochondrial cox1 gene

“…Attwood et al (2008) found that three of four studied Schistosoma mekongi populations from Cambodia and Southern Laos were distinguishable at cox1 and 12S mt loci. Furthermore, the unique haplotype patterns representing two evolutionary lineages with strong spatial specificity were detected for Ugandan Schistosoma mansoni from Lake Albert and Lake Victoria using DNA barcoding, sequence analysis of two partially overlapping cox1 regions-ASMIT (396 bp) and MORGAN (617 bp) (Stothard et al 2009). Morgan et al (2005) used partial fragments of cox1, rrnLrrnS, cytb-nad4L-nad4, and nad1 covering more than 2,500 bp of mtDNA to describe within-species diversity of S. mansoni originating from Africa and the New World.…”

“…RAPD was applied to estimate genetic variation of mammalian schistosomes within and among hosts or within and among populations (e.g., Dabo et al 1997;Davies et al 1999;Sire et al 2001). The population genetic studies involving different mt markers were also reported for Schistosoma parasites (Morgan et al 2005;Attwood et al 2008;Stothard et al 2009). …”