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Fascioliasis: the Invasive Stages of Fasciola hepatica in Mammalian Hosts

1964; Elsevier BV; Linguagem: Inglês

10.1016/s0065-308x(08)60587-4

2163-6079

Ben Dawes, D.L. Hughes,

Parasite Biology and Host Interactions

This chapter focuses on the various invasive stages of Fasciola hepatica in mammalian hosts. Some of these stages are in plentiful amounts, along with excysting flukes, free flukes in the intestinal lumen and flukes lying in the folds of the villi. Free flukes contract and extend the anterior region of the body in what can be called exploratory movement and on an artificial substratum the young flukes move rapidly by alternate use of the oral and ventral suckers. The amount of movement depends on the amount of extension, which the anterior region can command, as well as on the speed with which the suckers can be engaged and disengaged. Even before excystment is completed, the large and scanty cells of the caecal epithelium show an eosinophilic reaction and secretion droplets can be seen in the distal cytoplasm. Newly excysted flukes creep about over the mucosal surface, coming to lie in folds between the villi, and their browsings lead to the formation of lesions, which are minute and difficult to observe. Sites of penetration are inconspicuous but many instances of flukes already located within the villi are found, where the fluke excavates part of the core and compresses the remainder against the overlying epithelium. Flukes are also found in the submucosa, sometimes checking and turning as if to avoid some obstacle. Many more stages of penetration are found in the muscle layers of the intestines than in the mucosa and submucosa, which is not entirely due to time factors but more probably due to the greater difficulty, which the fluke has in penetrating this kind of tissue. Flukes soon aggregate beneath the muscles, which demonstrate that they find these layers more resistant to their browsing activities than those already encountered.