Human disease caused by dog heartworm.

Pulmonary infection with D. immitis is an infrequently reported cause of lung disease in humans. Approximately 80 cases have been reported in the United States, with increasing numbers reported in recent years. The largest single series from one institution is a series of 6 patients from Ochsner Clinic in New Orleans, Louisiana. Although our series consisted of 3 females and no males, the disease is detected and diagnosed in males twice as often. The usual age range is 40 to 60 years. No case has yet been seen in children. Unfortunately, it is essentially impossible to diagnose by clinical means. The definitive diagnosis can be made quite easily, however, by histologic examination which reveals the worm within the lesion. It should be noted that the parasites are seen in a minority of sections; therefore, diagnosis may be missed. As a result, given the setting of pulmonary infarction with granulomatous response, multiple sections of the lesion should be examined. Other larval worms also occurring in the lung which might be confused with D. immitis include Enterobius vermicularis, Wuchereria bancrofti, Brugia malayi, and Onchocerca volvulus. These, however, are much less common and are morphologically distinct from D. immitis. Also, it is easily distinguished from ascarids, strongyloids, and hookworm larvae which are much smaller than the dirofilarial worms and do not contain reproductive organs. In North American, the occurrence of fragments of nematode within a pulmonary infarct is essentially pathognomonic for PD.