Prevalence and distribution of trematodes hosted by Bithynia siamensis in Southern Thailand

This study aimed to investigate the occurrence of larval trematode infections in bithyniid snails across five provinces in southern Thailand. A total of 1,413 Bithynia siamensis snails were collected between October 2021 and October 2022 using handpicking and scooping methods. Among these, 844 were identified as B. s. siamensis and 569 as B. s. goniomphalos . The snail samples were examined for parasitic infections in the laboratory using shedding and crushing methods. Among the 27 sampling sites, snails from 6 sites were infected with various trematode species (infection rate: 4.95%, 70/1,413). Evaluation of the morphological and internal organ characteristics of the cercariae allowed for the categorization of the trematodes into five species of trematodes (belonging to four families). The identified species included Echinochasmus pelecani (family: Echinostomatidae), Echinostoma revolutum (family: Echinostomatidae), Haematoloechus similis (family: Haematoloechidae), Loxogenoides bicolor (family Lecithodendriidae), and Stictodora tridactyla (family: Heterophyidae), and the infection rates for these species were 3.26% (46/1,413), 0.35% (5/1,413), 0.42% (6/1,413), 0.78% (11/1,413), and 0.14% (2/1,413), respectively. The cercariae from the identified trematode species were studied for DNA analysis. The phylogenetic lineage reveals relationships among the species, confirming the morphological distinctions.