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.
Courtesy of Dr. Ronald Green.
Infected animals may have a chronic, deep, intermittent cough and eventually become weak and lethargic, although many infections pass unnoticed. Lung bullae may form, causing spontaneous pneumothorax. Finding the characteristic eggs in feces or sputum is diagnostic. Additional diagnostic testing such as an transtracheal wash may be performed to detect larvae or eggs. The location in the lungs may be determined with radiography. Aberrant infections can be identified serologically. P kellicoti ova may be found in fecal sedimentation.
Fenbendazole (50 mg/kg/day, PO, for 10–14 days) or less preferably albendazole (25 mg/kg, PO, twice a day for 14 days) reduce the number of eggs deposited and eventually kill the parasites. Praziquantel (25 mg/kg, PO, three times a day for 3 days) may also eliminate lung flukes in dogs.
