Visceral leishmaniasis (VL) is a systemic protozoal disease. It is considered one of the "neglected tropical diseases" by the World Health Organization (WHO). It is commonly called kala-azar (meaning "black fever" in Hindi) because some cases of VL, particularly in India, have been associated with generalized skin hyperpigmentation. It is also known as Dumdum fever and Assam fever.
The majority of cases (>90%) of VL are found in the following areas of the world: Eastern India, Nepal, Bangladesh, Sudan, South Sudan, Brazil, and Ethiopia. It disproportionately affects impoverished individuals.
Two species of Leishmania, Leishmania donovani and Leishmania infantum (known as Leishmania chagasi in South America), are causative agents for almost all cases of VL. The disease is transmitted by the bite of an infected sandfly. The parasite exists in 2 forms: the amastigote form (in humans) and the promastigote form (in sandflies). The amastigote form is a round or oval structure that consists of a nucleus and a DNA-containing body called the kinetoplast. The parasite has a predilection to infect the mononuclear phagocyte system (MPS), previously termed the reticuloendothelial system.
The incubation period varies from weeks to months. While the majority of infections tend to be subclinical, when symptomatic the disease often runs an insidious course and presents with fevers, weight loss, malnutrition, and hepatosplenomegaly. Lymphadenopathy is often seen in VL encountered in Sudan but is less common in India. Patients often appear emaciated, and children may present with growth retardation and severe wasting. VL may present acutely with high fevers, though this is not a common presentation.
Immunocompromised hosts such as HIV patients and organ transplant recipients are at increased risk for disseminated disease and multiorgan involvement. In fact, some cases of subclinical infection may surface when immunity wanes.
Specific diagnosis needs to be made in suspected VL, since clinical presentation is often nonspecific and the differential diagnosis is broad.
Common diseases that mimic VL include:
Tuberculosis – Fevers, weight loss, and malnutrition are common to both, but splenomegaly is more reflective of VL.
Tropical splenomegaly seen in chronic malaria may be mistaken for VL. Positive malarial smear will help distinguish these entities.
Histoplasmosis, especially the disseminated form, may be mistaken for VL. On microscopy, the yeast form of the fungus may appear like the amastigote form of Leishmania, but the presence of kinetoplast helps to differentiate the two.
Endocarditis or prolonged Salmonella bacteremia – Blood cultures would be positive in these. One should bear in mind, however, that superimposed bacterial infections may occur.
AIDS – HIV and leishmaniasis may coexist, and positive test for HIV infection should prompt one to test for VL in the right clinical setting.