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Microbiology · Hemoflagellates (trypanosomes and Leishmania)

Leishmania infantum !

  • Parasite
  • Exam priority: high

A Leishmania that invades the liver, spleen and bone marrow. It causes fever, a huge spleen and anemia, mostly in young children; usually fatal untreated.

Updated 2026-11-01

Also called: Leishmania chagasi, kala-azar, visceral leishmaniasis

At a glance

Shape
Oval amastigote in tissue; promastigote in the vector
Family
Trypanosomatidae
Type
Intracellular flagellated protozoan (macrophages of the reticuloendothelial system)
Stain
Giemsa on bone-marrow or spleen aspirate
Size
Amastigote about 2 to 4 µm

Morphology

  • Amastigotes inside macrophages of bone marrow, spleen, liver and lymph nodes.
  • Round nucleus and rod-shaped kinetoplast on Giemsa stain.
  • Belongs to the L. donovani complex; L. chagasi is the older name used in the Americas.

Transmission

  • Bite of female Lutzomyia sand flies (in Colombia, mainly Lutzomyia evansi and Lutzomyia longipalpis).
  • The dog is the main domestic reservoir.
  • Rarely transfusion, shared needles or congenital.

Reservoir: Domestic dog (main); Opossums and foxes

Vector: Female sand flies of the genus Lutzomyia.

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. The sand fly bites and deposits promastigotes in the skin.
  2. Macrophages engulf them and they turn into amastigotes.
  3. Amastigotes travel through the reticuloendothelial system to the spleen, liver, bone marrow and lymph nodes.
  4. There they multiply and cause hepatosplenomegaly and marrow failure.
  5. The sand fly becomes infected by biting a dog or person with parasites in the skin or blood.
  6. In the insect it turns into a promastigote and migrates to the proboscis.

Virulence factors

  • Tropism for macrophages of the spleen, liver and bone marrow.
  • Suppression of the Th1 response and interferon-gamma; malnutrition and HIV favor disease.
  • Reticuloendothelial hyperplasia and polyclonal hypergammaglobulinemia; splenic sequestration of blood cells.

Diseases it causes

  • Visceral leishmaniasis (kala-azar): prolonged fever, splenomegaly, pancytopenia and wasting; fatal without treatment. Leishmaniasis →

Clinical picture

  • Weeks of irregular fever, weight loss and a swollen abdomen.
  • Marked splenomegaly and hepatomegaly.
  • Pancytopenia: anemia, leukopenia and low platelets; bleeding and secondary bacterial infections.
  • Most common in malnourished children under 5 and in people with HIV.

Diagnosis

  • Bone-marrow aspirate (or spleen aspirate in expert centers) with Giemsa: amastigotes in macrophages.
  • Serologic tests, including the rK39 antigen rapid test.
  • NNN culture and PCR to confirm and type.
  • Pancytopenia and hypergammaglobulinemia as supporting clues.

Treatment

Liposomal amphotericin B is the preferred treatment in many guidelines; alternatives are pentavalent antimonials, amphotericin B deoxycholate and miltefosine, depending on country and species. Malnutrition, anemia and associated infections also need management.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Sand fly control in and around the home (spraying, clearing the surroundings).
  • Surveillance of canine leishmaniasis and insecticide collars for dogs in endemic areas.
  • Insecticide-treated nets and early diagnosis in children with prolonged fever.

Vaccine: There is no human vaccine.

Test yourself

Think of the answer, then tap the question to see it.

Which species causes visceral leishmaniasis in Colombia?

Leishmania infantum (formerly called L. chagasi), of the L. donovani complex.

What is the main domestic reservoir of L. infantum?

The dog, which can carry parasites in its skin and act as a source for sand flies.

Which sample is used to see amastigotes in visceral disease?

Bone-marrow aspirate (or spleen aspirate in expert centers), stained with Giemsa.

Which blood count findings suggest kala-azar?

Pancytopenia (anemia, leukopenia and thrombocytopenia), often with hypergammaglobulinemia.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Leishmaniasis (CDC, 2024); Leishmaniasis (WHO, 2023); Informe de Evento 2023 Leishmaniasis (Instituto Nacional de Salud (INS) Colombia, 2024); Clinical Care of Leishmaniasis | Leishmaniasis | CDC (CDC, 2024).

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