Leishmaniasis is caused by a protozoan of the genus Leishmania that includes many species, some of which cause more than one clinical syndrome. Leishmaniasis is best known in the Middle East but also occurs in the Far East (except Japan), various areas of Africa, Central and South America, and occasionally in the European side of the Mediterranean and in some islands of the Caribbean. There are three fairly well-defined syndromes: visceral (kala-azar), cutaneous (localized or widespread), and mucosal. Kala-azar is a chronic systemic disease most commonly associated with Leishmania donovani, Leishmania infantum, and Leishmania chagasi. Symptoms are fever, hepatosplenomegaly, normocytic-normochromic anemia, leukopenia, sometimes thrombocytopenia, hypergammaglobulinemia, and loss of cell-mediated immunity (delayed hypersensitivity). The reservoir of disease is dogs, wild canine species, rodents, and humans; the vector is the sandfly (Phlebotomus species in most areas but other species in South America). The organism infects mononuclear cells of the reticuloendothelial system. Incubation varies from 2 weeks to over 2 years, but most often is 3-8 months.

Diagnosis can be made by aspiration of commonly infected organs with Giemsa or Wright’s stain of an aspirate smear to detect organisms within monocyte cytoplasm. Sensitivity in one report was said to be 98% from spleen, 54%-86% from bone marrow, and 60% from liver or lymph nodes. Various serologic tests are available in large reference laboratories or public health laboratories. ELISA or IFA (fluorescent antibody) are most frequently mentioned. There is considerable variation between these tests because the antibodies are not raised against a standard antigen preparation. The various tests cross-react to greater or lesser degree with trypanosomiasis, schistosomiasis, malaria, leprosy, and cutaneous leishmaniasis.

Cutaneous leishmaniasis occurs in most areas that host kala-azar, and is usually subdivided into Old World and New World types. In the Americas, the major reservoir is forest small animals. A cutaneous ulcer develops at the site of the sandfly vector bite. A widespread form also exists. Mucosal leishmaniasis is the least common syndrome, occurs in Central and South America, and follows cutaneous leishmaniasis, involving the nose or mouth area. Diagnosis can be made from biopsy (with special stains for the organism); aspiration and stained smears; or serologic tests (similar to visceral leishmaniasis). Test sensitivity is said to be about 80%-90% (range, 62%-96%).