Molecular epidemiology of Schistosoma mansoni in Uganda: DNA barcoding reveals substantial genetic diversity within Lake Albert and Lake Victoria populations.

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.