Organism The sheep liver fluke Fasciola hepatica. Less commonly F. gigantica.
Clinical features The parasite has a predilection for the liver, piercing the gut wall and migrating through the liver substance to lie in the biliary passages. This migration and residence in the liver causes extensive damage, leading to fibrosis and cirrhosis.
Diagnosis is made by finding the very large egg in the stool, which is almost identical to that of Fasciolopsis (Fig. 9.1).
Transmission The life cycle is similar to Fas-ciolopsis in that eggs passed in the faeces liberate a miracidium on contact with water. The miracidium searches for and invades snails of the genus Lymnaea. After passing through sporocyst and redia stages, the cercaria encyst on grass or water plants (e.g. water cress). The normal life cycle is in sheep, humans becoming incidentally infected when contaminated water plants are eaten (Fig. 9.2). Cattle and goats also act as reservoirs.
Incubation period Probably 2-3 months.
Period of communicability Not transmitted from person-to-person.
Occurrence and distribution Worldwide distribution in sheep-rearing areas, especially the Andean highlands of Bolivia, Ecuador and Peru, the Nile delta region of Egypt and northern Iran. F. gigantica is found in Africa and the Western Pacific; 2.5 million are probably infected in the world, with up to 60% of the population in highly endemic areas.
Control and prevention In known endemic areas, careful control is required in the growing and consumption of water plants such as cress. Animal faeces should not be used to fertilize water plants. The close association of humans and sheep or other domestic animals greatly increases the opportunity for infection.
Treatment Triclabendazole at 10 mg/kg single dose, which can be repeated after 12 h.
Surveillance Sheep should be examined at regular intervals and treated.
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