Parasites and Biliary stones

Opisthorchiasis ٣٢
Life cycle:
The adult worms of Opisthorchiasis live in the intra- and extra-
hepatic bile ducts, gall bladder, and rarely in the pancreatic duct. They
attach to the wall of these ducts by the oral and ventral suckers under the
regulatory function of the circular and radius muscles. Embryonated eggs
containing ciliated miracidium laid from gravid worms are passed
through the bile into the duodenum and excreted with faeces into the
external environment. After reaching freshwater of natural reservoirs,
these embryonated eggs do not hatch until they are ingested by Bithynia
snails into the digestive tracts where hatching occurs and then miracidia
transform to sporocysts. Rediae and cercariae are produced by the asexual
reproduction of germinal cells in sporocysts and rediae, respectively.
Free-living cercariae, after exit the snail will attach, penetrate and
transform to metacercariae encysted mainly in the muscle of about 18
susceptible species of fish in the family Cyprinidae (Harinasuta and
Harinasuta, 1984 and Waikagul, 1998). Metacercariae are infective to
final hosts including humans, dogs and cats when they ingest raw or
inadequately cooked fish. After ingestion, the metacercaria is digested by
gastric and intestinal juices, respectively (figure 12). Excysted juvenile
flukes at the duodenum then migrate up through the ampulla of Vater and
the common bile duct into the intra-hepatic bile ducts where they mature
and fertilize. Some worms are formed in the common bile duct, cystic
duct and gall bladder. The life span of Opisthorchiasis viverrini in human
is not known, however, it may be over 25 years as recorded in C. sinensis
(Attwood and Chou, 1978).