In 2005, Sri-aroon et al. (2005) reportedthat the infection rates of O. viverrini in B. siamensis goniomphalos varied from 0.61 to 1.3%. More recently however, average prevalence of 3.04% has been reported, with the highest prevalence in Sakon Nakhon Province of 6.93% (Kiatsopit et al., 2012).