Visceral leishmaniasis: a difficult diagnosis and unusual causative agent.

In a young man who had a prolonged fever of unknown origin, hepatosplenomegaly, and progressive pancytopenia, stained smears, blood-agar cultures of bone marrow, and serologic testing for antileishmanial antibodies were negative. Biopsies from liver and bone marrow were uninformative. Visceral leishmaniasis was diagnosed only after splenectomy, when amastigotes were finally cultured from the spleen. The parasite was shown to be an unusual leishmanial parasite, possessing a mixture of intrinsic biochemical and serologic characteristics displayed independently by Leishmania tropica and Leishmania donovani sensu lato, the latter being the usual cause of visceral leishmaniasis. After splenectomy, parasites were also demonstrated in stained bone marrow aspirate smears. Recovery was uneventful after treatment with antimony for 28 days. Visceral leishmaniasis can be a cause of fever of unknown origin and should be considered in its differential diagnosis in endemic areas.