Infection with the trematode (parasitic worm) Paragonimus. More than 10 species of trematodes (flukes) of the genus Paragonimus infect humans, the most common being Paragonimus westermani, the oriental lung fluke. While P. westermani occurs in the Far East, other species of Paragonimus are encountered in Asia, the Americas, and Africa.
Human infection with P. westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor the parasite. The parasites excyst in the duodenum, penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults. The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. Infections may persist for 20 years in humans.
The acute phase (invasion and migration) may be marked by diarrhea, abdominal pain, fever, cough, urticaria (hives), hepatosplenomegaly (enlargement of the liver and spleen), pulmonary abnormalities, and eosinophilia (an elevated level of eosinophils, a type of white blood cell). During the chronic phase, pulmonary manifestations include cough, expectoration of discolored sputum, hemoptysis (spitting up blood), and chest radiographic abnormalities. Extrapulmonary locations of the adult worms result in more severe manifestations, especially when the brain is involved.
Diagnosis is based on microscopic demonstration of eggs in stool or sputum, but these are not present until 2 to 3 months after infection. Biopsy may allow diagnostic confirmation and species identification when an adult or developing fluke is recovered. Praziquantel is the drug of choice to treat paragonimiasis. Bithionol is an alternative drug for treatment of this disease.
See also: Pleural Effusions