Due to neglect of proper hygienic measures, the water buffaloes are subjected to many snail-borne parasitic diseases. Amongst these diseases, paramphistomiasis due to bile duct fluke Gigantocotyle explanatum has been reported from many tropical countries including Pakistan. This parasite has been reported to cause various degrees of hepatic dysfunction in the buffaloes.

In the present study, 450 buffaloes were examined for the record of prevalence of explanatum infection. The age dependent prevalence recorded in 3 age groups i.e. upto 2 years, 2-5 years and above 5 years, was 18.2%, 30.5% and 61.4% respectively. Majority of the buffaloes in age groups upto 2 years and 2-5 years were lightly infected (100% and 78.8% respectively). Moderate infection was observed in 2-5 years and above 5 years age groups (2 1.2% and 33.3% respectively). Heavy infection (45%) was only observed in buffaloes above 5 years of age.

The pathological lesions produced by G. explanatum were observed in infected livers from groups A(upto 2 year), B(2-5 years) and C(above 5 years). Grossly, the notable changes in the size, color, consistency and appearance were recorded only in heavily infected buffaloes above 5 years of age (group C). The parasites were mostly seen attached to the common bile duct mucosa. Only in heavily infected buffaloes the parasites were seen attached to intra-hepatic bile ducts mucosa. Lentil sized nodules were observed at the site of attachment of the parasites. The walls of affected bile ducts were thickened and lumina were dilated to accomodate the parasites.

The microscopic lesions included degeneration and desquamation of epithelium of affected bile ducts. The subepithelial mucous glands showed hyperplasia. Mono-nuclear cells infiltration was observed in the subepithelial tissues. Proliferation of fibrous connective tissue was seen on the outermost layer of the affected bile ducts. Disruption of hepatic cords and dilatation of sinusoids were mostly observed in the areas adjacent to affected bile ducts. The portal tracts showed fibro-cellular reaction.

The serum samples from infected groups A, B and C and control groups A1, B1 and C1 were analysed for the study of serum total bilirubin patterns. The serum bilirubin level gradually increased with the increase in degree of parasitic infestation. The serum bilirubin level increased significantly in infected buffaloes above 2 years of age (group B and C) as compared to infected buffaloes below 2 years of age (group A). In the case of buffaloes above 5 years of age (group C), there was a significant increase in serum total bilirubin level in infected group as compared to control group. The major cause of increase in bilirubin level, in this case, was heavy parasitic infestation.