Abstract

A dense, 2-cm mass was discovered by X-ray and surgically removed from the lower lobe of the left lung of a 42-year-old man in a city on the West Coast of Japan. It was found to be an infarct-like lesion caused by an organized thrombus containing two worms, markedly different in size, dead, and somewhat degenerate but with well-preserved diagnostic features of the young adult stage of Dirofilaria immitis, the dog heartworm. This apparently is the 16th recorded case of pulmonary dirofilariasis of man, the first from Japan.