Diagnostic features of zoonotic filariae in tissue sections

The diagnostic features in tissue sections from patients with zoonotic filarial infections are reviewed. In general, two types of infections are recognized: 1) those presenting radiologically in healthy patients as coin lesions, which are usually removed because a clinical diagnosis of carcinoma of the lung is made and infarcts containing Dirofilaria immitis parasites in pulmonary arteries are found; and 2) those presenting as subcutaneous nodules, in which D. tenuis, a parasite from raccoons, D. repens, from dogs and cats, D. ursi , from bears, and Onchocerca spp, from horses or cattle, require delineation. Moreover, nodules that on microscopic examination are seen to be lymph nodes may harbor Brugia spp. The geographic distribution of these infections, with emphasis on the United States, is discussed.