By Gary M. White, MD
Dirofilariasis is the infection of a human with Dirofilaria, a zoonotic filarial nematode. Dirofilaria is a parasite common in dogs, cats, wolves, bears, porcupines, and raccoons. Humans are accidental hosts.
The life cycle is as follows. A mosquito bites a raccoon or dog and ingests the microfilaria. The mosquito then bites a human and lays the filariae which migrate to the subcutaneous tissue. Human beings are rare, accidental dead-end hosts. Human to human or human to arthropod transmission does not occur.
A solitary subcutaneous nodule is characteristic. It is flesh-colored to erythematous and variably tender. It may be quite mobile. In one patient, the nodule migrated from the foot to the shin to the shoulder to the elbow! [JAAD 1996;35;260]. One should get a CXR as the organism D. immitis may migrate to the lungs.
Consultation with an infectious disease expert is appropriate. Excision of the cutaneous nodule is usually curative. In the majority of cases, only a single parasite is present and systemic antiparasitic treatment is not necessary.
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