One of largest flukes: 30 x 13 mm
The adult parasites reside in the intra-hepatic bile ducts, produce eggs, and the eggs are passed in the host's feces. After passing through the first intermediate host (a snail), cercariae encyst on vegetation. The definitive host is infected when it eats the contaminated vegetation. The metacercaria excysts in the definitive host's small intestine, and the immature worm penetrates the small intestine and migrates through the abdominal cavity to the host's liver. The juvenile worm penetrates and migrates through the host's liver and finally ends up in the bile ducts. The migration of the worms through the host's liver, and the presence of the worms in the bile ducts, destroying and feeding on liver cells and blood-are responsible for the pathology associated with fascioliasis- called liver rot, and also severe anemia. Humans often infected in specific areas where watercress/aquatic vegetation is grown and eaten.
Clonorchis sinensis (Chinese liver fluke) It is estimated that 19 million human cases of this infection exist in the Far East. The disease is widespread in China, Japan, Taiwan, Korea and Vietnam. Humans acquire the disease by eating raw fish. Other reservoir hosts include cats, tigers, dogs, fox, badgers and mink. Again the life cycle is parallel to F. hepatica, with a few variations. No daughter redia are produced from the mother redia. Instead cercariae produced will leave the snail host to find and penetrate a suitable fish host. Once in the fish, the cercaria will become an encysted metacercaria. Infection in humans is acquired by eating raw or poorly cooked fish, especially those produced in fish farms (aquaculture systems) where "night soil" (human feces) is used.
The metacercariae excyst in the host's small intestine, and the juvenile worm migrates up the common bile duct into the bile ducts inside of the liver. The worms can live at least 10 years, and possibly as long as 20 years. The adult worms measure between 10 and 25 mm in length. The do not actually live in the host's liver, but are found in the bile ducts. The parasite causes thickening of the lining of the bile duct and an inflammatory response in the surrounding liver tissue. In heavy infections the bile duct epithelium can also be eroded, and the parasite's eggs will enter the liver tissue; in such cases the eggs are surrounded by a fibrotic capsule (granuloma). Heavy infections can also result in stenosis (narrowing or blockage) of the bile ducts. Since the parasites can live for years and the number of parasites tends to increase as a person ages, the damage to the liver and bile duct tends to accumulate over time and can result in death.
Common parasite of pigs and humans More common where human nightsoil used as fertilizer Lives in intestine, not liver. Metacercariae found on underwater vegetation: including cultivated waterchestnut, lotus, bamboo, and other edible plants. Inflammation at site of attachment- excessive mucous production, Excessive numbers block passage of food, interfere with secretion of digestive enzymes Ulceration, hemorrhage, intestinal abscesses, if these rupture can cause peritonitis.
Digeneans: All life cycles involve a mollusc and a vertebrate All life cycles are similar but different All life cycles are a variation of one theme. Adult-egg-miracidium-[black box of sprorocyst/rediae] Cercariae leave snail (usually): 1) penetrate host (definitive or intermediate) 2) encyst on vegetation