Epidemiological situation and molecular identification of cercarial stage in freshwater snails in Chao-Phraya Basin, Central Thailand

Objective: To investigate the prevalence of cercarial trematode infection in snails and to examine the reconstruction of the phylogenetic relationship to explain the molecular system of cercarial stage trematodes to estimate the infection rate of in the definite host from the Chao-Phraya Basin.Methods: The snails were collected from 10 provinces of the Chao-Phraya Basin,Thailand by stratified sampling method. The snails were examined for cercarial infection by the crushing method. All DNA specimens were amplified with internal transcribed spacer 3(ITS3) and ITS4 primer based on PCR technique. The sequence data were aligned and used to reconstruct the phylogenetic tree by unweighted pair-group method with arithmetic means with 10 000 bootstraps.Results: The overall rate of cercarial infection was found to be 5.90%(122/2 067). Snails in the family Thiaridae were found to be in the highest prevalence followed by Lymnaeidae, Bithyniidae, Planorbidae, Viviparidae, and Ampullariidae, respectively, while the Buccinidae family(Clea helena) did not reveal any infections. The frequently found species of cercariae were parapleurolophocercous cercariae, cercariae and megarulous cercariae. The monophyletic tree separated the snails into five groups comprised of Heterophyidae, Strigeidae, Lecithodendriidae, Philophthalmidae and Echinostomatidae using the sequence of Angiostrongylus cantonensis as an out-group.Conclusions: This study was the first to report on cercarial infection in the Chao-Phraya Basin, Thailand. This revealed that a high variety of freshwater snails were infected by cercariae stage trematodes with a high prevalence. The sequence data of ITS2 can be used to investigate the phylogenetic relationships of trematodes at the family level and in each clade of different families separated by the definitive hosts.

New scope on the relationship between rotifers and Biom phalaria alexandrina snails

Objective:To investigate the effect of rotifer internalization into snail tissue on the development of schistosomes.Methods:Susceptible laboratory-bred Biomphalaria alexandrina(B.alexandrina)snails were exposed to lab-maintained rotifers;Philodinaspp.,two weeks before and after being infected with Schistosoma mansoni(S.mansoni)miracidia.The consequent histopathological impact on snail tissues and cercarial biology were investigated before and after emergence from snails.Results:Contamination of B.alexandrinasnails with philodina,two weeks before miracidial exposure,was found to hinder the preliminary development of S.mansonicercariae inside the snail tissues.Furthermore,when snails were contaminated with rotifers two weeks post miracidial exposure;growth of already established cercariae was found to be retarded.The consequent influence of internalized rotifers within the snail tissue was clearly reflected on cercarial em ergence,activity and infectivity along the four weeks duration of shedding.In the present study,comparison of snail histopathological findings and altered cercarial biology observed between the experimental and control groups indicated that the rotifers may have affected the levels of snail's energy reservoirs,which eventually was found to have had an adverse impacton reproduction,growth and survival of the parasite within the snail host,coupled with its performance outside the snail.Conclusions:In future biological control strategies of schistosomiasis,ritifers should be considered as a parasitic scourge of humanity.

Human-water interactions associated to cercarial emergence pattern and their influences on urinary schistosomiasis transmission in two endemic areas in Mali

Background Mali is known to be a schistosomiasis-endemic country with a limited supply of clean water.This has forced many communities to rely on open freshwater bodies for many human-water contact(HWC)activities.However,the relationship between contact with these water systems and the level of schistosome infection is cur-rently receiving limited attention.This study assessed human-water interactions including cercarial emergence pat-tern and their influences on urinary schistosomiasis transmission in two communities in the Kayes district of Mali.Methods We carried out a parasitological study frst in children in September 2021,then a cross-sectional study of quantitative observations of human-water contact activities in the population,and finally a study of snail infectiv-ity at contact points in September 2022.The study took place in two communities,Fangoune Bamanan and Diakalel in the Kayes region of western Mali.The chronobiological study focused on cercarial release from naturally infected snails.Released cercariae were molecularly genotyped by targeting the cox1 region,and the ITS and 18S ribosmal DNA gene(18S rDNA)regions of the DNA.Links between sociodemographic parameters,human water-contact points and hematuria were established using multivariate statistical analysis or the logistic regression model.Results The main factor predisposing the 97 participants to water contact was domestic activity(62.9%).Of the 378 snails collected at 14 sampling sites,27(7.1%)excreted schistosome cercariae,with 15.0%(19/126)at Fangoune Bamanan and 3.3%(8/252)at Diakalel.The release of Schistosoma cercariae shows three different patterns in Fangoune Bamanan:(i)an early release peak(6:00-8:00 AM),(i)a mid-day release peak(10:00 AM-12:00 PM)and(ili)a double peak:(6:00-8:00 AM)and(6:00-8:00 PM)cercariae release;and two release patterns in Diakalel:early release(6:00-8:00 AM)and(il)mid-day release(12:00-2:00 PM).All cercariae released during early diurnal(6:00-8:00 AM)or nocturnal emission patterns(6:00-8:00 PM)were hybrids parasite having an cox1 S.bovis or S.curassoni associ-ated with an ITS and 18S rDNA of S.haematobium while the cercariae released during diurnal,or mid-day patterns(8:00AM-6:00PM)werepure S.haematobium.Conclusions Our study showed that domestic activity is the main source of exposure in the Kayes region.Two and three cercariae emission patterns were observed at Diakalel and Fangoune Bamanan respectively.These results suggest that the parasite adapts to the human-water contact period in order to increase its infectivity.