It is important to note in this context that trematodes infecting humans, especially liver fluke and intestinal flukes, are highly prevalent in Southeast Asian countries (Wongratanacheewin et al. 2001; Chai et al. 2005). These infections have a major public health impact. It has been reported that the highest degree of infections with trematodes were discovered in the gastrointestinal tract of humans living in the north region of Thailand (Pungpak et al. 1998, Radomyos et al. 1998) and the most metacercarial species were found in cyprinoid fish in the north and northeastern regions (Srisawangwong et al. 1997b, Sukontason et al. 1999). The liver fluke Opisthorchis viverrini can cause chalangiocarcinoma, a kind of cancer in gall bladder (Sripa et al. 2010), while the intestinal fluke Haplorchis taichui is a possible agent of irritable bowel syndrome-like symptoms (Watthanakulpanich et al. 2010). However, Thai people have considerably underestimated these trematodes by continually eating Thai traditional food prepared from raw freshwater fish (Chuboon et al. 2005). So the prevalence of trematodes in Thailand has been a continual problem until now