Laboratory Diagnosis of Visceral Leishmaniasis

The group of diseases known as the leishmaniases are caused by obligate intracellular protozoa of the genus Leish- mania (39). Natural transmission of leishmania is carried out by a certain species of sandfly of the genus Phlebotomus (Old World) or Lutzomyia (New World). These are present in three different forms: (i) visceral leishmaniasis (VL), (ii) cutaneous leishmaniasis, and (iii) mucocutaneous leishmaniasis. The vis- ceral form, also known as black sickness or kala-azar in Asia, is characterized by prolonged fever, splenomegaly, hepatomeg- aly, substantial weight loss, progressive anemia, pancytopenia, and hypergammaglobulinemia and is complicated by serious infections. It is the most severe form of the disease and, left untreated, is usually fatal. Although confirmed cases of VL have been reported from 66 countries, 90% of the world's VL burden occurs on the Indian subcontinent and in Sudan (12, 21, 65, 80). After recovery, some patients (50% in Sudan and 1 to 3% in India) develop post-kala-azar dermal leishmaniasis (PKDL), which requires prolonged and expensive treatment (57, 83). PKDL patients also play an important role in VL transmission (77). VL is typically caused by the Leishmania donovani complex, which includes three species: L. donovani, Leishmania infantum, and Leishmania chagasi. The clinical fea- tures of VL caused by different species are different, and each parasite has a unique epidemiological pattern. On the Indian subcontinent, the disease is almost exclusively caused by L. donovani. The initial report of Leishmania tropica causing VL in India (61) was refuted by us and others (74, 78). L. infantum is responsible for VL in children in the Mediterranean basin. However, due to increasing prevalence of human immunode- ficiency virus (HIV) infection in this region, HIV-VL coinfec- tion in the adult population is being reported frequently. L. chagasi causes VL in children in Latin America, where lymph- adenopathy is a dominant clinical feature. L. tropica, the caus- ative organism of Old World cutaneous leishmaniasis, is re- ported to produce visceral disease in nonimmune persons (41). Similarly, visceralization by Leishmania amazonensis, has also been reported (28). Clinical manifestations of all forms of VL change from time to time, and this is the case more so in AIDS patients (8, 21, 42, 43, 48).