Opisthorchiasis is an endemic parasitic disease in northeastern Thailand. The concomitant occurrence of the parasite and cholangiocarcinoma as well as the incidence of such tumors are higher in that part of the country than in other areas. Nitrosating agents, nitrosatable substances, and nitrosamine compounds are commonly present in several kinds of stable foods in that region. To study the interactions between the parasite and the nitroso compounds, we divided Syrian golden hamsters into four groups: Group 1, untreated; Group 2, dimethylnitrosamine (DMN, 0.0025% or 25 ppm)-treated; Group 3, 100 metacercariae-treated; and Group 4, DMN (0.0025% or 25 ppm) plus 100 metacercariae-treated groups. The animals that received both DMN and parasites (Group 4) developed cholangiocarcinoma (100%) and cholangiofibrosis (100%). The tumor was not observed in the group that received either DMN (Group 2) or parasites alone (Group 3), although cholangiofibrosis was found in some animals in the DMN group (Group 2). It is postulated that cholangiocarcinomas in these animals arose because the DMN exerted a carcinogenic effect on the altered proliferating epithelial cells of bile ducts that had been stimulated by the parasite. These findings suggest that the combination of DMN ingestion and liver fluke infestation may play an important role in the carcinogenesis of the intrahepatic duct neoplasms in human beings.
This investigation was supported in part by National Research Council of Thailand.