Paragonimus kellicotti and P westermani usually are found in cysts, primarily in the lungs of dogs, cats, and several other domestic and wild animals. They also have been found rarely in other viscera or the brain. Infection is most common in China, southeast Asia, and North America. P westermani is a parasite of people and other animals in China and other countries in the Far East.
The adult flukes are fleshy, reddish brown, oval, and ~14 × 7 mm. The eggs are golden brown, oval, distinctly operculated, and ~100 × 60 μm. The eggs pass through the cyst wall, are coughed up, swallowed, and passed in the feces. The life cycle includes several snails as the first intermediate host, and crayfish or crabs as the second. Dogs and cats become infected by eating raw crayfish or crabs that contain the encysted cercariae. After penetrating the intestinal wall and wandering in the peritoneal cavity, the young flukes pass through the diaphragm to the lungs, where they become established.
Infected animals may have a chronic, deep, intermittent cough and eventually become weak and lethargic, although many infections pass unnoticed. Finding the characteristic eggs in feces or sputum is diagnostic. The location in the lungs is ascertained by radiography. Aberrant infections can be identified serologically.
Fenbendazole (50 mg/kg/day, PO, for 10–14 days) or less preferably albendazole (25 mg/kg, PO, bid for 14 days) reduce the number of eggs deposited and eventually kill the parasites. Praziquantel (25 mg/kg, PO, tid for 3 days) may also eliminate lung flukes in dogs.
Last full review/revision November 2013 by Ned F. Kuehn, DVM, MS, DACVIM