Seventeen new and four reclassified cases of zoonotic filariasis in the United States are reported, and eighteen previously reported cases are reviewed. Worms recovered from the 39 infected persons were of six morphological types: In 11 cases, worms morphologically indistinguishable from Dirofilaria immitis were found in the heart (2 cases) or in infarct-like lesions of the lungs; in 24, worms of the morphological type referred to as Dirofilaria conjunctivae were in subcutaneous nodules or swellings; and Dirofilaria of a different type was found in one case, Brugia-like in one, and Dipetalonema-like in two.
All of the infected persons were adult, 31 (80%) were female, and 32 or more acquired the infection in the South, mostly in Florida. The worms in all cases were sexually mature but unmated; more than two-thirds had died in the tissues. In most cases the symptoms or signs of infection were of short duration, with onset apparently coinciding with the worm's loss of vitality.
Present address: Tulane University, Delta Regional Primate Research Center, Covington, Louisiana.