The Intestinal Fluke Fasciolopsis

Organism The large human fluke Fasciolop-sis buski.

Clinical features The adult worm lives in the small intestines and produces damage by inflammatory reaction at the site of attach ment. This sometimes leads to abscess and haemorrhage, but as well as these local effects, the parasite produces toxins. These can lead to oedema, weakness and prostration, ending fatally in the debilitated child.

Diagnosis is made by finding the egg in faeces, a giant among parasites (Fig. 9.1). The egg is indistinguishable from Fasciola hepatica (see Section 9.4).

Transmission The eggs are passed in faeces either directly into water or are washed there following rains, where they hatch and liberate a miracidium, which must find a snail of the genus Segmentina. Developing first into a sporocyst, then a redia, numerous cercaria are produced. On leaving the snail, the cercaria encyst on water plants that are subsequently eaten raw by humans (Fig. 9.2). These plants include the water calthrop (Trapa sp.), the water chestnut (Eliocharis tuberosa) and the water bamboo (Zizania aquatica). Beds of these water plants are often grown in ponds fertilized by human sewage, providing considerable opportunity for transmission. Even if the foods are subsequently cooked, they are often first peeled with the teeth so that cercariae are still swallowed.

A reservoir of infection is maintained in pigs, sheep, cattle and other domestic herbivores. Infection is particularly high in pig-rearing areas. Humans also act as reservoirs.

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