Cercarial dermatitis outbreak caused by ruminant parasite with intermediate snail host: schistosome in Chana, South Thailand

Abstract

A cercarial dermatitis outbreak occurred in Chana district, Songkhla Province, South Thailand, between August and October 2020. A total of 359 cases with cercarial dermatitis were confirmed with three cases of skin biopsy. The species of potential trematodes from infected snails were investigated, and the prevalence of infestation with schistosomes was described. As part of our ongoing studies of trematode diversity in freshwater systems, using morphological traits and sequence data to differentiate species, this study aimed to provide insights into the parasite species that cause cercarial dermatitis in the outbreak area and improve our understanding of parasite species distribution. Snail samples were collected in December 2020 and September and October 2021. Five main areas of outbreaks were investigated, and snails were collected by scooping and examined for infection with cercariae. The cercariae were characterized on the basis of morphological features. We found two species of snails to be infected, viz. Indoplanorbis exustus and Bithynia siamensis siamensis, with infection rates of 2.05% (12/586) and 7.93% (23/290), respectively. Three species of trematodes were found in B. s. siamensis, viz. Gastrothylax crumenifer, Astiotrema monticellii, and Loxogenes liberum. Moreover, three species of trematodes were found in Indoplanorbis exustus, viz. Clinostomum giganticum, Echinostoma spiniferum, and Schistosoma indicum. The latter is a ruminant schistosome, which causes the outbreak of cercarial dermatitis in the area. They were genetically analyzed using the internal transcribed spacer subunit II region to confirm the species identity at generic and infrageneric levels.

High prevalence of natural infection by the ruminant blood fluke Schistosoma spindale in the intermediate snail host Indoplanorbis exustus in Uttaradit, Northern Thailand

“…We observed two morphological types of trematode cercariae: Furcocercous and Echinostome. Our observed rate of cercarial infection in I. exustus was higher than that previously recorded in Thailand (2.05%–5.5%) [ 30 , 31 ] and neighboring countries such as Malaysia (1.7%) [ 32 ] and Vietnam (38.5%) [ 33 ]. The diversity of trematode larvae in I. exustus was quantified.…”

“…In a recent study, Krailas et al . [ 31 ] reported that I. exustus from Chana, Southern Thailand, were infected with three types of cercariae: S. indicum , Echinostoma spiniferum , and Clinostomum giganticum .…”

“…[ 30 ] and Krailas et al . [ 31 ]. The observed echinostome cercaria was identified as A. malayanum through molecular analyses of COX1 sequences and morphological characteristics.…”

Population genetic structure of Indoplanorbis exustus (Gastropoda: Planorbidae) in Thailand and its infection with trematode cercariae

“…Currently, I. exustus is widely distributed in Asia, Africa, and the Caribbean region [1][2][3][4]. This organism has been reported as an intermediate host for various trematode parasites (Trematoda: Digenea) in veterinary and medical fields [5,6]. I. exustus is known as the intermediate host for Schistosoma indicum, S. nasale, and S. spindale, as well as other trematodes such as Clinostomum giganticum and Echinostoma spp.…”

“…I. exustus is known as the intermediate host for Schistosoma indicum, S. nasale, and S. spindale, as well as other trematodes such as Clinostomum giganticum and Echinostoma spp. [5,6]. Moreover, I. exustus has been reported in association with outbreaks of cercarial dermatitis in humans in Thailand, Malaysia, Laos, and India [6][7][8][9].…”