EQUIVOCAL EVIDENCE OF COMPLETE CARCINOGENICITY AFTER REPEATED INFECTION OF SYRIAN-HAMSTERS WITH OPISTHORCHIS-VIVERRINI

The effects of repeated infection with Opisthorchis viverrini on liver lesion development in male and female Syrian hamsters were investigat ed over a 1-yr period. Ten monthly intragastric applications of 50, 25 , 13, or 0 parasite metacercariae resulted in pronounced proliferative and inflammatory lesions involving the first- and second-order ducts in response to the presence of adult worms. Despite the development of small numbers of putative preneoplastic areas of cholangiofibrosis an d morphologically altered hepatocellular foci, no neoplastic lesions w ere evident at sacrifice after 1 yr. The results thus suggest that par asite infestation is itself not strongly carcinogenic if at all but, r ather, that it exerts a marked promoting influence on cholangiocellula r and hepatocellular tumor development in the hamster via chronic irri tation and increased cell turnover.