Dirofilaria repens manifesting as a breast nodule. Diagnostic problems and epidemiologic considerations

Human dirofilarial infections characteristically manifest as pulmonary 'coin' lesions or as subcutaneous nodules. Reported is a case of subcutaneous Dirofilaria infection that first manifested as a painful breast nodule, necessitating excisional biopsy and frozen section interpretation to rule out incipient carcinoma. Histologic examination revealed a viable, adult female Dirofilaria repens, a nematode commonly found in dogs and cats throughout parts of Europe, Africa, and Asia. The patient, a Greek national, had been traveling in Greece and Italy within the previous 8 months. Dirofilariasis is seen infrequently in the United States, and when present is usually caused by the endemic species D. immitis or D. tenuis. Several other species also may infect humans but are rarely seen or may be misidentified as one of the more common species. Identification of dirofilariae from tissue sections is difficult, but knowledge of the parasite's geographic distribution and the patient's travel history are particularly helpful.