PREVALENCE OF TREMATODE LARVAE IN INTERMEDIATE HOSTS: SNAILS AND FISH IN KO AE SUB-DISTRICT OF KHUEANG NAI, UBON RATCHATHANI PROVINCE, THAILAND.

Ko Ae Sub-district of Khueang Nai, Ubon Ratchathani Province, Thailand is located in an endemic area for Opisthorchis viverrini and other fish-borne zoonotic trematodes (FZT) infection. This study shows the status in Ko Ae Sub-district of FZT infection based on availability of intermediate hosts and necessary requirements for the transmission of FZT. A cross-sectional survey of intermediate hosts of FZT, including Bithynia siamensis goniomphalos and cyprinoid fish, was conducted from April 2013 to December 2014. Examination of 1,000 snails revealed 3.4% were infected with trematode cercariae, with a density of infection greater than 100 cercariae per infected snail. Six groups of morphologically-distinguishable trematode cercariae were identified, namely, cystophorous, echinostome, furcocercous, mutabile, parapleurolophocercous, and xiphidio, the latter being the most predominant type. Among 250 cyprinoid fish samples with metacercariae present at their caudal fins and examined for FZT by pepsin digestion, metacer- cariae of Haplorchis taichui, H. pumilio, and Centrocestus formosanus were found. Unidentified metacercariae collected from fish caudal fins were subsequently shown using a PCR-based assay to be C. formosanus. No infection by O. viverrini in the intermediate hosts, Bithynia siamensis goniomphalos and cyprinoid fish was evident. The study provides new information regarding trematode larvae infection in the primary and secondary intermediate hosts of FZT in this area of Thailand.