Visceral leishmaniasis (VL) is a parasitic disease found in tropical and subtropical areas. It is a chronic systemic disease that mainly affects children under five years of age; it may be associated with malnutrition and other conditions of immunosuppression such as HIV-AIDS. If adequate treatment is not initiated in a timely manner, it can progress to death in 90% of cases.
VL is caused by intracellular protozoan parasites of the genus Leishmania. In the Americas, Leishmania infantum (syn. L.chagasi) is the species involved in VL.
Visceral Leishmaniasis. Paciente con pérdida de peso y presencia de hepatoesplenomegalia. Credits: Costa, JML, CPq GM-Fiocruz, Brasil. (Haga clic en la imágen para ampliar)
Source of Infection
In urban and rural areas, the domestic dog (Canis familiaris) is the main reservoir. In the wild, foxes (Cerdocyon thous and Lycalopex vetulus) and certain marsupials (Didelphis spp.) are the identified reservoirs.
In the Americas, the main vector of VL is the phlebotomine sandfly species Lutzomyia longipalpis, but Lu. evansi is also an important vector in Colombia and Venezuela, and Lu. cruzi is the vector in the municipality of Corumbá, on the border between Brazil and Bolivia.
Congenital and parenteral transmission (through needle-sharing among drug addicts) have been reported. There is no direct transmission from person to person.
Signs and Symptoms
The incubation period can range from 10 days to 24 months, with an average of 2-6 months. The infection is characterized by a wide clinical spectrum, which may range from mild (oligosymptomatic) to moderate and severe clinical manifestations.
The classic manifestations of VL include fever, splenomegaly (enlargement of the spleen, manifested in the great majority of patients), hepatomegaly (enlargement of liver), pallor (caused by severe anemia), leucopenia (low white blood cell count), and weight loss. Other signs and symptoms include respiratory problems or gastrointestinal disturbances such as vomiting and diarrhea; in severe cases there is malnutrition and lower limb edema, which may progress to anasarca (extreme generalized edema). Other important signs are bleeding from the nose or mouth, jaundice and fluid buildup in the abdomen. In these patients, death is usually determined by bacterial infection or bleeding.
Clinical: high clinical suspicion of disease is given to people from endemic areas with a persistent disease and unexplained fever accompanied by suggestive signs and symptoms.
Laboratory: immunological and parasitological tests are performed.
The immunological test currently available at the primary level is the rapid immunochromatographic test based on recombinant rK39 antigen, but the indirect immunofluorescence (IIF) and enzyme immunoassay (ELISA) is also used in other levels of care. Parasitological tests are performed by detecting parasites in infected tissues, mainly in the bone marrow, through direct examination or isolation in culture (in vitro). Molecular tests detect Leishmania DNA through the PCR method.
VIsceral Leishmaniasis visceral. Presencia de hepatomegalia y esplenomegalia. Credits: Costa, JML, CPq GM-Fiocruz, Brasil (Haga clic en la imagen para ampliar)
Medications used for the treatment of VL are the pentavalent antimonials, liposomal amphotericin B and amphotericin B. Generally pentavalent antimonials are the most used in the treatment of visceral leishmaniasis. However, the choice of medication should consider the clinical conditions of the patients, the presence of co-infections and pregnancy.
Prevention and control
There is no vaccine to prevent infection.
For the human population: Recommended measures for personal protection are aimed at reducing contact with vectors, in particular: avoid outdoor activities from dusk to dawn, the use of mosquito nets; use of protective clothing and insect repellents. People with clinical manifestations of the disease should be treated as early as possible.
For vector control: Preventive measures are directed towards integrated management actions in environmental sanitation, same as those for cutaneous leishmaniasis. The safe use of residual insecticide spraying is indicated as a control measure.
To control the urban reservoirs: Recommended preventive measures are the use of mosquito-proof meshes in dog kennels to also keep out the sandflies and the use on dogs of personal protective collars impregnated with insecticide. In the Americas, dogs are the main reservoir of visceral leishmaniasis and maintain the parasite in urban environment. Therefore, in areas with endemic transmission conducting serological surveys in dogs is recommended and when a dog is positive for the parasite, humane euthanasia is indicated.