Prevalence of cercarial infections in freshwater snails and morphological and molecular identification and phylogenetic trends of trematodes

Objective:To investigate the prevalence of cercarial infections in freshwater snails from several water sources in Nakhon Nayok,Nonthaburi,and Pathum Thani provinces of Central Thailand,and to reconstruct a phylogenetic tree for improved understanding of the relationships in the cercarial stage.Methods:The snail specimens were collected from 34 total sampling sites and investigated for cercarial infections using the crushing method.The cercarial specimens were classified and used for the phylogenetic tree analysis using the Internal Transcribed Spacer 2(ITS2).Results:A total of 1921 snail specimens were classified into five families and seven species.The results showed that four snail species were identified as intermediate hosts of the larval stages of trematodes,with an overall prevalence of infection of 2.45%(47/1921).The infected snail specimens included five groups of the cercarial type:cercariaeum cercariae,echinostome cercaria,megalurous cercaria,parapleurolophocercous cercaria,and xiphidiocercariae.This is particularly true of xiphidiocercariae,which was found to be the dominant type among cercarial infections in bithyniid snails by approximately 38.00%.With regard to molecular identification,the phylogenetic tree was reconstructed using the neighbor-joining method with 10000 bootstraps and separated the trematodes into three clades:Echinostomatoidea,Microphalloidea and Opisthorchioidea.Conclusions:The study reveals a high prevalence of cercarial infection for each cercarial type and maturation into a definite trematode genus and delineates morphological characteristics and evolutionary trends among each larval trematode in Nakhon Nayok,Nonthaburi and Pathum Thani provinces.In addition,the ITS2 sequence data of cercariae could be used to examine classification of these species at the family level.

Types of trematodes infecting freshwater snails found in irrigation canals in the East Nile locality,Khartoum,Sudan

Background:The planorbid freshwater snails of the two genera,Biomphalaria and Bulinus-have been vigorously studied due to the role they play as intermediate hosts of schistosomiasis.In Sudan specifically,most studies have focused on the chemical and ecological control of the two genera,but few studies have looked at their biological control.This study explored the coexistence of other species of freshwater snails and the two genera along with their trematode infections in relation to a number of environmental factors in the East Nile locality,Khartoum state,Sudan.Methods:Freshwater snails from irrigation canals(abueshreens)were sampled monthly from January 2004 to December 2005.The snails were examined for trematode infections by cercarial emergence immediately after collection and then weekly for an additional four weeks to allow for the maturation of prepatent infections.Vegetation cover in the study sites as well as the physicochemical characteristics of the water,including temperature,were also recorded.Results:A total of 10,493 snails,representing seven species,were collected.The most abundant species was Biomphalaria pfeifferi,representing 48.6%of the sample.Overall,14.1%of the snails were found to be shedding some type of cercariae.Five species were found to have infections;among these the Bulinus truncatus species was found to be the most heavily infected,with an overall prevalence of 46.2%.Double infections were recorded in only two B.truncatus snails and one Cleopatra bulimoides snail.Twenty different morphotypes of cercariae were recorded,seven of which appeared not to conform to previously described cercariae from Africa.Xiphidiocercariae type 1 was the most common type of cercariae recovered,accounting for 44.3% of all infections.The density of snails tended to be lower during the summer months than the winter months,except for M.tuberculata snails,which were not affected by seasonal changes.Conclusion:The findings of this study indicate that besides schistosomes,other larval trematodes are found,and some use the same intermediate hosts as the schistosomes.Further studies should be conducted to determine whether some of these trematodes could be manipulated for the biological control of schistosomiasis.

Hidden diversity revealed in the freshwater snails,Bythinella and Pseudamnicola,in the Island of Crete

Crete with its complex geomorphological history is the island with the highest number of endemism observed in animal and plant taxa throughout the Aegean archipelago.While other groups of organisms within Crete are well-studied,the freshwater gastropod fauna still remains poorly investigated.Bythinella and Pseudamnicola,are 2 genera of freshwater springsnails,both present on the island,inhabiting springs and other freshwater habitats.Here,we conduct a comprehensive study on the distribution of the different genetic lineages of the 2 gastropod genera in order to assess the mode of their differentiation on the island and infer the actual number of species present in the island.Towards these aims,sequence data from the mitochondrial gene were used and analyzed within a phylogenetic framework.For Bythinella,our results strongly support at least 5 delineated Bythinella spp.inhabiting Crete,which correspond to the already described species from previous studies with the addition of a new one.Bythinella analyses reveal an old time-frame of differentiation with vicariant phenomena being more likely the main drivers shaping the present-day distribution of the genus’genetic lineages.For Pseudamnicola,our data indicate the presence of at least 2 delineated Pseudamnicola spp.with a differentiation more consistent to an isolation-by-distance pattern of a relatively recent origin.Dispersion processes followed by isolation of the populations and/or recent speciation,seem to be the underlying process for the current distribution of Pseudamnicola lineages.

Towards interruption of schistosomiasis transmission in sub-Saharan Africa:developing an appropriate environmental surveillance framework to guide and to support‘end game’interventions

Schistosomiasis is a waterborne parasitic disease in sub-Saharan Africa,particularly common in rural populations living in impoverished conditions.With the scale-up of preventive chemotherapy,national campaigns will transition from morbidity-to transmission-focused interventions thus formal investigation of actual or expected declines in environmental transmission is needed as‘end game’scenarios arise.Surprisingly,there are no international or national guidelines to do so in sub-Saharan Africa.Our article therefore provides an introduction to key practicalities and pitfalls in the development of an appropriate environmental surveillance framework.In this context,we discuss how strategies need to be adapted and tailored to the local level to better guide and support future interventions through this transition.As detection of egg-patent infection in people becomes rare,careful sampling of schistosome larvae in freshwater and in aquatic snails with robust species-specific DNA assays will be required.Appropriate metrics,derived from observed prevalence(s)as compared with predetermined thresholds,could each provide a clearer insight into contamination-and exposure-related dynamics.Application could be twofold,first to certify areas currently free from schistosomiasis transmission or second to red-flag recalcitrant locations where extra effort or alternative interventions are needed.