Hyperplasia of the bile duct in fascioliasis and its relation to the problem of nutrition in the liver-fluke, Fasciola hepatica L.

Abstract

Histological investigations of the bile ducts of various hosts of F. hepatica during the early stages of infection, when the flukes are burrowing in the liver and have not yet reached the bile ducts, indicate that subtle changes are brought about, probably by chemical agencies and as a result of the inflammatory process, in the bile ducts of the hosts. The transitory appearance of minute cytoplasmic blebs at the free margins of the epithelial cells seems to inaugurate an intense hyperplasia of the epithelium with tubular ingrowths and adenomatous development of glandular tissue, and an associated fibrosis which produces a thick underlying layer of dense fibrous tissue. At the time of entry of the flukes into the biliary system the hyperplastic epithelium is intact, but soon the spines and suckers of the flukes abrade the superficial cells until this part of the duct is completely denuded. It is suggested that as a result of the inflammatory reaction, the fluke has been provided with a ‘pasture’ of hyperplastic epithelium and connective tissue on which it may continue to browse for considerable periods without necessarily affecting the host adversely. Tissue debris is found in the contents of the bile duct and similar homogenized materials occur in the caecal contents of the fluke. Previous researches have shown that the fluke will feed on various tissues, and it is suggested that this tissue-feeding habit persists during its life in the bile duct. These results agree with the findings of Müller (1923) but are at variance with the results obtained by other investigators, as is shown in discussion. The hyperplasia of the bile duct is not characteristic of fascioliasis, occurring also in clonorchiasis, opisthorchiasis and dicrocoeliasis, and in these and possibly other instances it is probably intimately connected with the nutrition of the flukes concerned.