Hight prevalent of Opisthorchis viverrini infection and coincident Haplorchis metacercariae in cyprinid fishes in upper northeastern region of Thailand

Cyprinid fishes are commonly acted as second intermediate hosts of Opisthorchis viverrini and Haplorchis spp. This research investigated the prevalence and intensity of both parasites in cyprinid species. This process is regularly used as a guideline for disease surveillance and as a preventive measure in the Upper Northeastern region of Thailand. Fish samples were collected from both lentic and lotic water sources between November 2020 and October 2021, and classified them by their species. Acid pepsin-HCL solution was used to digest the individual samples and create a build-up of precipitate in order to view metacercariae using a stereomicroscope. A total of 3583 fish were caught and classified into 23 species. Out of these fish, 5.49% of them were found O. viverrini, 26.54% Haplorchis taichui, 10.04% Haplorchis pumilio, and 9.29% Haplorchoides sp. Ten species of fish were observed to have been infected with O. viverrini. Amongst the collected fish, M. obtusirostris had the highest prevalence of infection at 52.94%, while B. gonionotus had only 1.71%. The prevalence of O. viverrini infection was highest at 27.41% in Udon Thani Province. No prevalence of O. viverrini infection was observed in Bueng Kan Province. High prevalence of O. viverrini infection in cyprinid fishes was found in both lentic and lotic water sources in almost all provinces in the region. The prevalence of infection and intensity depended on the fish species and fish habitats.