Visceral leishmaniasis (VL) is a systemic protozoal disease. It is considered one of the "neglected tropical diseases" by the World Health Organization (WHO), disproportionately affecting poor and marginalized populations with limited access to health care. It is also 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.

In 2022, the WHO reported that 77 countries are endemic to VL and that 89% of reported cases are from 8 countries: India, Sudan, South Sudan, Brazil, Somalia, Kenya, Ethiopia, and Yemen. In the same year, 69 VL cases were reported in Europe and North America in migrant health clinics from patients who had traveled from an endemic area.

VL is caused by 2 species of Leishmania: Leishmania donovani in Africa and Asia and Leishmania infantum (known as Leishmania chagasi in South America) in the Mediterranean Basin, the Middle East, Central Asia, South America, and Central America. The disease is transmitted between mammalian hosts 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 onset can be acute or insidious with an incubation period that varies from weeks to months. While the majority of infections tend to be subclinical, when symptomatic, the disease often presents with fever, 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.

Immunocompromised hosts, such as patients with HIV 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. In endemic areas, HIV screening should be mandatory in all patients presenting with VL. Studies in East Africa recommend that patients presenting with severe and atypical manifestations of VL require different diagnostic and management approaches since the existing rapid diagnostic tests have been shown to be less sensitive in HIV-positive patients than in HIV-negative patients.

Related topics: cutaneous leishmaniasis, mucocutaneous leishmaniasis, post kala azar leishmaniasis