An unexpected parasite in bone marrow: Uncommon presentation of a common disease.

Elephantiasis, also known as filariasis, is a severe public health issue in India. Microfilariae in the bone marrow smears are an unusual and incidental finding. Every peripheral blood and bone marrow aspirate smear must be screened for microfilariae in endemic areas to identify asymptomatic carriers. Here, we report a case of a 50-year-old man who presented with pyrexia of unknown origin. He had mild pallor and right-side inguinal lymphadenopathy. Peripheral blood showed anemia and leukocytosis with neutrophilia. Other serological tests, radiological examination, and aspiration cytology from the lymph node were inconclusive. The bone marrow aspirate smears incidentally displayed microfilaria, and the inguinal lymph node demonstrated an adult filaria worm. The association of microfilaria infection with pyrexia of unknown origin (PUO) and peripheral blood neutrophilia has been rarely reported in the literature. The patient recovered from fever and weakness with antifilarial medication and hematinics.