Worms and Human Disease

Map 4. Distribution of Clonorchis sinensis and Opisthorchis viverrini.
have been found in a single fish.
Metacercarial cysts measure 140 µm
120 µm and are infective in about 23 days.
When fish are eaten raw or undercooked,
the metacercarial cysts hatch out in the
human duodenum and the young flukes
migrate up the bile-ducts, maturing in 3–4
weeks. The adult flukes can live for up to
26 years but on average survive for 10
years (Chen et al., 1994).
CLINICAL MANIFESTATIONS
The Trematodes 39
The majority of infections (about 70%) are
symptomless and the presence of worms is
only diagnosed at autopsy, when up to 100
flukes may be found in the bile-ducts.
Moderate infections, due to the presence of
100–1000 flukes, result in diarrhoea, abdominal
discomfort and some splenomegaly. When
a heavy infection, which may consist of many
thousands of worms (the maximum recorded
being 21,000), is contracted at one time, there