Opisthorchis viverrini: liver changes in golden hamsters maintained on high and low protein diets

Two groups of hamsters maintained on eight high (25.6%) or low (5.3%) content protein diets were infected with 50 Opisthorchis viverrini metacercariae by intragastric inoculation. Three animals from each group were sacrificed at 14-day intervals over a 32-week period. Two groups of non-infected control animals maintained on identical diets were killed at similar intervals. Histological examination revealed qualitatively similar pathological responses to the parasite in both diet groups, but overall the low protein diet group had the more severe lesions. Two weeks after infection, second order bile ducts showed epithelial focal necrosis, reactive hyperplasia and folding of the bile duct epithelium with some periductal fibrosis. Periductal inflammatory cells were predominantly eosinophils and lymphocytes at this time, changing after six weeks to predominantly lymphoblast and plasma cell infiltrates. Central bile ducts showed maximal concentric fibrosis at 12 weeks and this was considerably more pronounced in high protein fed animals. The small peripheral bile ductules proliferated and by four weeks post-infection, adjacent portal tracts appeared linked together, until at eight weeks some of the livers were nodular. The degree of bile ductule proliferation was markedly more pronounced in the low protein fed animals such that by 12 weeks parts of the peripheral liver substance was obliterated by proliferating ductules. No tumours or evidence of premalignant lesions were detected in livers from any of the infected animals, but it is likely that the infection period was rather too short for malignant transformation to ensue. The possible pathogenetic mechanisms operating in this animal model of opisthorchiasis are discussed with particular reference to the disease in man.