Comparison of the pathogenesis of challenge and single infections with Fasciola hepática in sheep

Abstract

An experiment was designed to investigate differences in the pathogenesis of fascioliasis in sheep receiving two infections, as compared to those receiving only one infection. The materials used, and the methods applied to monitor the clinical pathological changes during the course of the infections are detailed.

Changes in the haematological picture and serum biochemistry during the course of the experiment were consistent with those described by other workers as occurring during infection with Fasciola hepática. In particular, elevated eosinophil counts were recorded, reaching peak values at 9 to 10 weeks post infection. Marked increases in serum enzyme levels were also observed® These reached a peak at either five or eight weeks post infection, depending on the group.

Gross pathological changes in the livers of the experimental animals are described in detail. There was marked individual variation in this parameter in that the livers of two of the sheep showed severe parenchymal changes while those of the other sheep showed only mild changes. This variation could not be attributed to the number of flukes recovered from each liver.

Differences in the numbers of flukes recovered and in the degree of development of those flukes, between the challenge and control groups were not seen.'

No evidence for acquired resistance in sheep to F. hepática infection was demonstrated, but there was some reduction in the severity of the pathological changes during the early stages of challenge infection.