Morphological and molecular characteristics of trematode cercariae isolated from the freshwater snails collected from three paragonimiasis endemic areas in Manipur, India

Abstract

A study was conducted to identify and characterize trematode cercariae infecting freshwater snails in three paragonimiasis endemic areas namely, Luwangsangbam matai, Motbung, and Moreh of Manipur, India, from 2020 to 2024. A total of 9467 snails belonging to seven species namely Bortia costula (2404), Filopaludina bengalensis (1869), Paludomous pustulosa (1474), Racesina luteola (1147), Melanoid tuberculota (891), Radix rufescens (869) and Indoplanorbis exustus (814) were collected and examined for cercarial infection using the shedding and crushing methods. The overall prevalence of trematode infection in snails was 0.26%, with the highest infection rate observed in Moreh (0.41%), followed by Motbung (0.36%) and Luwangsangbam Matai (0.09%). Among the snail species, Melanoides tuberculata showed the highest infection rate (0.90%), whereas Indoplanorbis exustus and Paludomous pustulosa were not infected. Morphological examination revealed nine different morphological types of cercariae: Lophocercous (1), Apharyngeate ocellate furcocercariae (1), Gymnocephalous (2), Xiphidio (1), Furcocercous (2), and Echinostomous (2). Molecular analysis based on 18 S rDNA sequencing and phylogenetic analysis identified six trematode species: Euryhelmis costaricensis, Trichobilharzia stagnicolae, Haematoloechus sibiricus, Australapatemon burti, Echinostoma revolutum, and Hypoderaeum conoideum. Seasonal variations in cercarial infection were observed, with higher rates from late spring to summer and lower rates in winter and early spring. This study provides baseline data on trematode-snail dynamics in the freshwater ecosystems of Manipur, which can be used for future epidemiological research and targeted control strategies.