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Dirofilaria Ursi-Like Parasites Acquired by Humans in the Northern United States and Canada: Report of Two Cases and Brief Review

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  • 1 *School of Public Health and Tropical Medicine, Tulane University, New Orleans, Louisiana 70112,
  • 2 †infectious Disease Unit, Medical Services, Massachusetts General Hospital, Boston, Massachusetts 02114,
  • 3 ‡Winchester Hospital. Winchester, Massachusetts 01890

Two cases of subcutaneous dirofilariasis acquired in Ontario and Vermont are reported. The parasites in these and eight cases previously reported from the northern United States and Canada are classified as resembling Dirofilaria ursi, a primarily subcutaneous parasite of bears, or D. subdermata of porcupines, in the same region. A distinguishing morphological feature of the D. ursi-like group is the presence of distinct longitudinal cuticular ridges regularly and widely spaced on the outer surface, and usually evident even when the worms are necrotic. In the 10 known cases, all patients were women, and the usual location of nodules containing the worms was the scalp or a covered part of the upper body where blackfl.ies, the intermediate hosts of D. ursi, normally feed.