Abstract:
Cercarial dermatitis outbreaks have been reported in Surat Thani and Songkhla provinces, Thailand. Gastropods serve as the intermediate hosts for this snail-transmitted disease. The aim of this study was to examine the snail species and cercariae found in snails from the southern Thailand, with a hypothesis about cercariae and intermediate host that cause cercarial dermatitis in areas near the disease outbreak. Snail samples were collected from agricultural water sources in five provinces: Chumphon, Surat Thani, Nakhon Si Thammarat, Phatthalung, and Songkhla. Snails were collected from 29 locations in October 2021 and October 2022. A total of 3,342 snails were classified into 21 species. Among them, 82 snails had the ability to serve as intermediate hosts for cercariae, including Bithynia siamensis goniomphalos, B. s. siamensis, Gyraulus convexiusculus, Indoplanorbis exustus, and Radix rubiginosa. The infection rates were 1.74% (10/574), 7.27% (61/839), 1.14% (2/176), 0.25% (2/802), and 4.02% (7/174), respectively. The cercariae were classified based on morphological characteristics and internal organs, resulting in 7 types and 13 species: (1) Echinochasmus pelecani (2) Echinoparyphium recurvatum (3) Echinostoma spiniferum (4) E. revolutum (5) Schistosoma indicum (6) S. spindale (7) Clinostomum giganticum (8) Diplostomum baeri eucaliae (9) Stellantchasmus falcatus (10) Haematoloechus similis (11) Loxogenes liberum (12) Loxogenoides bicolor (13) Ophthalmoxiphidiocercariae. Molecular analysis based on the ITS2 markers indicated clear differentiation between the cercariae according to their species. This study provides insights into the biodiversity of snail hosts and their relationships with cercariae, revealing that I. exustus and R. rubiginosa were infected with the cercariae of the S. indicum group, which can cause disease in ruminant animals and human cercarial dermatitis.