The Prevalence of Human Intestinal Fluke Infections, Haplorchis taichui, in Thiarid Snails and Cyprinid Fish in Bo Kluea District and Pua District, Nan Province, Thailand

Traditionally, people in the Nan Province of Thailand eat raw fish, exposing them to a high risk of getting infected by fish-borne trematodes. The monitoring of helminthiasis among those people showed a high rate of infections by the intestinal fluke Haplorchis taichui , suggesting  that also an epidemiologic study (of the epidemiology) of the intermediate hosts of this flat worm would be useful. In this study freshwater gastropods of thiarids and cyprinid fish (possible intermediate hosts) were collected around Bo Kluea and Pua District from April 2012 to January 2013. Both snails and fish were identified by morphology and their infections were examined by cercarial shedding and compressing. Cercariae and metacercariae of H. taichui were identified by morphology using 0.5 % neutral red staining. In addition a polymerase chain reaction of the internal transcribed spacer gene (ITS) was applied to the same samples. Among the three thiarid species present were Melanoides tuberculata , Mieniplotia (= Thiara or Plotia) scabra and Tarebia granifera only the latter species was infected with cercariae, with an infection rate or prevalence of infection of 6.61 % (115/1,740). In the 10 species of cyprinid fish (viz. Barbodes schwanenfeldi, Garra cambodgiensis, Hypsibarbus salweenensis, Mystacoleucus marginatus, Osparus pulchellus, Poropuntius deauratus, P. normani, Scaphiodonicthys acanthopterus, Systomus orphoides and S. stolitzkaenus ), metacercariae were found in all of them. Interestingly, B. schwanenfeldi, M. marginatus, P. deauratus, P. normani and S. orphoides had very high infection rates. Both morphometric and molecular identification confirmed those cercariae and metacercariae to represent the heterophyid Haplorchis taichui . Therefore, this study showed the high prevalence of this parasite both in its intermediate hosts as well as in humans. In order to prevent human infection, H. taichui has to be controlled.