Visceral leishmaniasis is one of the forms of infection caused by the protozoan parasite Leishmania. The majority of cases occur in the South American, African, and Asian continents. Blood-sucking sand flies are the vectors responsible for transmission of this microorganism to the human hosts. Infection is characterized by pancytopenia (anemia, thrombocytopenia, neutropenia), hepatosplenomegaly, fever, and severe immunosuppression that can lead to fatal opportunistic diseases without early recognition. The diagnosis is made through clinical findings, laboratory studies, and either direct or indirect microbiological methods.
The clinical presentation of visceral leishmaniasis possesses a long incubation period (ranging from a few weeks to even years), a nonspecific symptomatology, and a variable clinical course, and may pose a diagnostic challenge    . The two main signs of visceral leishmaniasis are fever and pancytopenia, both being almost universally present in all patients who suffer from this type of leishmaniasis  . Fever can range anywhere between 37-40°C and often has an irregular pattern of occurrence . On the other hand, pancytopenia (including thrombocytopenia, anemia, and leukopenia) causes weakness and severe immunosuppression, thus promoting various superinfections of bacterial, viral, or parasitic origin   . Opportunistic infections are, in fact, the leading cause of death from visceral leishmaniasis, with mortality rates being as high as 75%-95% in the absence of an early diagnosis and appropriate therapy . The term "kala-azar" (meaning black death) is used to describe visceral leishmaniasis that is restricted to the Old World and caused by Leishmania donovani . Wasting and poor general condition induced by pancytopenia are seen in advanced stages of the disease . In addition to fever and bone marrow suppression, hepatosplenomegaly is another important sign in visceral leishmaniasis, seen in up to 85-100% of patients in some studies . Lymphadenitis is a less frequent manifestation  .
A detailed patient history and a thorough physical examination are the first and perhaps crucial steps for making an initial diagnosis of visceral leishmaniasis. The vast majority of patients (> 90%) who suffer from visceral leishmaniasis come from six countries of the world: India, Bangladesh, Sudan, South Sudan, Ethiopia, and Brazil   . For this reason, the physician should conduct a detailed patient history that will cover recent travel to endemic countries, as well as possible exposure to sand flies in the last few years. After assessing the course of symptoms and their progression during the interview, a meticulous physical examination, particularly abdominal palpation, will reveal either hepatomegaly, splenomegaly, or both. In order to solidify the diagnosis, laboratory and microbiological tests need to be conducted. A basic complete blood count (CBC) is sufficient to detect pancytopenia, while directed diagnostic testing for Leishmania is broadly divided into indirect and direct methods. Serological testing (specifically enzyme-linked immunosorbent assay, or ELISA, and fluorescence antibody testing) is widely used as the main indirect test that has good sensitivity/specificity    . Detection of antigen rk39 through ELISA is a very reliable procedure and is used by many laboratories over the world  Conversely, identification of the parasite by light microscopy and Giemsa staining from blood samples is a relatively easy and effective procedure, while lymph node, liver, spleen, or even bone marrow samples might be used for evaluation, but the risks of bleeding (particularly in the case of spleen and bone marrow) often outweigh the benefit of confirming the diagnosis histologically    .