Paragonimus westermani, also known as the Asian Lung Fluke, is a trematode that may infect humans who eat raw crab or crayfish. It is most prominent in Asia and South America. Adult worms are 7.5- 12mm long and 4-6mm wide.
Paragonimus westermani metacercaria are ingested by humans in snails or crustacea. The metacercaria excyst in the stomach and penetrate the intestinal wall. It moves to the abdominal cavity, penetrates the diaphragm and moves into the pleural cavity. The male follows the female through this path and the two adults live together in cystic cavities in the lungs. An unembryonated egg is found in sputum and in feces if swallowed. The egg embryonates in water and miracidium hatch and penetrate a snail. Sporocysts form in snail tissue and develop into redia. Cercaria form in crustaceans and develop into metacercaria, their infective stage.