Date Published: March 19, 2008
Publisher: Public Library of Science
Author(s): Stephen W. Attwood, Farrah A. Fatih, E. Suchart Upatham, David Blair
Abstract: BackgroundSchistosomiasis in humans along the lower Mekong River has proven a persistent public health problem in the region. The causative agent is the parasite Schistosoma mekongi (Trematoda: Digenea). A new transmission focus is reported, as well as the first study of genetic variation among S. mekongi populations. The aim is to confirm the identity of the species involved at each known focus of Mekong schistosomiasis transmission, to examine historical relationships among the populations and related taxa, and to provide data for use (a priori) in further studies of the origins, radiation, and future dispersal capabilities of S. mekongi.Methodology/Principal FindingsDNA sequence data are presented for four populations of S. mekongi from Cambodia and southern Laos, three of which were distinguishable at the COI (cox1) and 12S (rrnS) mitochondrial loci sampled. A phylogeny was estimated for these populations and the other members of the Schistosoma sinensium group. The study provides new DNA sequence data for three new populations and one new locus/population combination. A Bayesian approach is used to estimate divergence dates for events within the S. sinensium group and among the S. mekongi populations.Conclusions/SignificanceThe date estimates are consistent with phylogeographical hypotheses describing a Pliocene radiation of the S. sinensium group and a mid-Pleistocene invasion of Southeast Asia by S. mekongi. The date estimates also provide Bayesian priors for future work on the evolution of S. mekongi. The public health implications of S. mekongi transmission outside the lower Mekong River are also discussed.
Partial Text: Schistosomiasis in humans along the lower Mekong river (specifically Cambodia and southern Laos) was first recognized in 1957  and has proven a persistent public health problem in the region . The species involved is the parasitic blood fluke Schistosoma mekongi Voge, Buckner & Bruce 1978, which uses the caenogastropod snail Neotricula aperta (Temcharoen, 1971) (Gastropoda: Pomatiopsidae: Triculinae) as intermediate host. Published records identify the following foci of S. mekongi transmission: Ban Hat-Xai-Khoun, Khong Island, southern Laos  ; Kratié in Kratié Province, northeastern Cambodia, approximately 180 km downstream of Khong Island ; and San Dan, Sambour District, also in Kratié Province  (Fig. 1A). Prior to 1994 up to 40% of the admissions to Kratié hospital were schistosomiasis-related and deaths were common place . Following mass treatment with the anthelmintic Praziquantel, the prevalence in school children in Kratié Province fell from 40% in 1994 to 14% in 1995 . In Laos, at Khong Island, a nine year Praziquantel intervention programme reduced the prevalence among village children from 51% to 27% .