infectious diseases
Paragonimiasis
Pathophysiology of Paragonimiasis
Eggs passed in sputum or feces develop for 2 to 3 weeks in freshwater before miracidia (first larval stage) hatch. The miracidia invade snails; there, they develop, multiply, and eventually emerge as cercariae (free-swimming larvae). Cercariae penetrate freshwater crabs or crayfish and encyst to form metacercariae. Humans become infected by eating raw, pickled, or poorly cooked crustaceans. Metacercariae excyst in the human gastrointestinal tract, penetrate the intestinal wall, and move into the peritoneal cavity, then through the diaphragm into the pleural cavity; they enter lung tissue, become encapsulated, and develop into hermaphroditic adult worms, which produce eggs. Adult worms grow to about 7.5 to 12 mm by 4 to 6 mm. From the lungs, eggs exit the body in sputum that is coughed up and spit out or swallowed and passed in stool. Worms may also reach the brain, liver, lymph nodes, skin, and spinal cord and develop there. However, in these organs, the life cycle cannot be completed because the eggs have no way to exit the body. Adult flukes may persist for 20 to 25 years. Other hosts include pigs, dogs, and a variety of feline species. 