Population genetic structure and geographical variation in Neotricula aperta (Gastropoda: Pomatiopsidae), the snail intermediate host of Schistosoma mekongi (Digenea: Schistosomatidae)

Abstract

BackgroundNeotricula aperta is the snail-intermediate host of the parasitic blood-fluke Schistosoma mekongi which causes Mekong schistosomiasis in Cambodia and the Lao PDR. Despite numerous phylogenetic studies only one DNA-sequence based population-genetic study of N. aperta had been published, and the origin, structure and persistence of N. aperta were poorly understood. Consequently, a phylogenetic and population genetic study was performed, with addition of new data to pre-existing DNA-sequences for N. aperta from remote and inaccessible habitats, including one new taxon from Laos and 505 bp of additional DNA-sequence for all sampled taxa,.Principal findingsSpatial Principal Component Analysis revealed the presence of significant spatial-genetic clustering. Genetic-distance-based clustering indicated four populations with near perfect match to a priori defined ecogeographical regions. Spring-dwelling taxa were found to form an ecological isolate relative to other N. aperta. The poor dispersal capabilities suggested by spatial-genetic analyses were confirmed by Bayesian inference of migration rates. Population divergence time estimation implied a mid-Miocene colonisation of the present range, with immediate and rapid radiation in each ecogeographical region. Estimated effective population sizes were large (120–310 thousand).ConclusionsThe strong spatial-genetic structure confirmed the poor dispersal capabilities of N. aperta—suggesting human-mediated reintroduction of disease to controlled areas as the primary reason for control failure. The isolation of the spring-dwelling taxa and ecogeographical structure suggests adaptation of sub-populations to different habitats; the epidemiological significance of this needs investigation. The large effective population sizes indicate that the high population densities observed in surveyed habitats are also present in inaccessible areas; affording great potential for recrudescence driven by animal-reservoir transmission in remote streams. Mid-Miocene colonisation implies heterochronous evolution of these snails and associated schistosomes and suggests against coevolution of snail and parasite. Heterochronicity favours ecological factors as shapers of host-parasite specificity and greater potential for escape from schistosomiasis control through host-switching.

Chromosome-scale genome of the human blood fluke Schistosoma mekongi and its implications for public health

“…Our explored diverse proteases (degradome) implicated in almost all physiologic and pathological processes may therefore hold promising therapeutic potential. Some studies involving strong drug discovery efforts targeting above mentioned peptidases are already in place to develop anti-schistosomal treatment [ 7 , 14 ]. To identify potential differentiation-related genes, we scanned the homologs of sexual development-related genes from S. japonicum in S. mekongi (Additional file 1: Table S12).…”

“…S. mekongi is mainly distributed in Cambodia, Myanmar, Thailand [ 6 ], Laos, and other regions near the Mekong River and its tributaries (Additional file 1 : Fig. S1), where it poses a threat to about 1.5 million people [ 7 ]. A wide spread of S. mekongi associated with increased risk to the public's health has been recently predicted [ 8 ].…”

Schistosoma japonicum complex: relatedness of the parasites and relatedness of its intermediate hosts in evolution

“…10 Schistosoma mekongi infects Neotriculla aperta snails. 17 Schistosoma ovuncatum and S. sinensium infect Tricula spp. snails.…”

Female Genital Schistosomiasis: A Neglected among the Neglected Tropical Diseases

“…Six major species in the genus Schistosoma significantly contribute to disease morbidity in humans: S. mansoni , S. japonicum , S. intercalatum , S. guineensis , and S. mekongi (mainly responsible for the hepato-intestinal form), and S. haematobium (for the urogenital form). Despite their varied geographical distribution, all species are contracted through direct contact with schistosome-contaminated freshwater inhabited by specific snails, the intermediate hosts [ 8 , 9 , 10 ]. Infection occurs during water-related activities such as personal hygiene, laundry, recreational practices, and agricultural work, alongside inadequate waste management systems [ 6 ].…”