Leishmaniases are parasitic diseases, which are transmitted by the blood‐sucking sand flies as the vectors. These diseases are largely zoonotic, but considered as anthroponotic in some endemic sites. The reservoir animals include canines, rodents, edentates and other wild animals. A spectrum of clinical manifestations is associated with these diseases, ranging from self‐healing cutaneous lesions to facial mucocutaneous disfiguration to visceralization with fatal consequence. According to the World Health Organisation, there are 12 million cases of these diseases in approximately 90 countries with an annual incidence of approximately 2 million. Treatment of leishmaniases depends on very few drugs for chemotherapy, which are either expensive or toxic and have lost effectiveness due to drug‐resistance. The causative agents are the trypanosomatid protozoa Leishmania, widespread in tropical and subtropical areas. Intraphagolysosomal parasitism of macrophages by these parasites is a key feature in considering molecular mechanisms of their virulence relevant to developing effective drugs and vaccines needed.

Key Concepts:

  • Trypanosomatid protozoa in the genus of Leishmania cause Leishmaniases.

  • They have evolved mechanisms to live in macrophage endosomes/lysosomes.

  • The diseases are wide‐spread mainly in tropical and subtropical areas of the world.

  • The diseases are largely zoonotic and transmitted by blood‐sucking sand flies.

  • Reservoirs include domestic and wild animals, for example, canines, rodents & edentates.

  • Clinically, there are cutaneous, mucocutaneous and visceral Leishmaniasis.

  • The clinical spectrum results from host immunopathology to Leishmania infection.

  • Chemotherapy relies on toxic drugs and loses its effectiveness to drug‐resistance.

  • Drug development programs by targeting unique parasite enzymes are very few.

  • Control programs include the use of anti‐vector pesticide/repellents.

Keywords: Leishmania; promastigotes; amastigotes; kala azar; espundia; leishmanization

Figure 1.

Leishmania life cycle in mammalian hosts (upper) and in sandfly vectors (lower). Redrawn (not to scale) after Chang, Fong and Bray (1985). Mammalian stage: (1) delivery of infective promastigotes into mammalian skin by the bite of sandfly vector; (2) phagocytosis of promastigotes by a macrophage; (3) fusion of a promastigote‐containing phagosome with the lysosome; (4) full differentiation of promastigote into amastigote in the phagolysosome of the infected macrophage; (5) amastigote replication in a parasite‐containing or parasitophorous vacuole; (6) continuing replication of intravacuolar amastigotes in small individual or large communal parasitophorous vacuoles; (7) degeneration (symbolically shown by dotted lines) of heavily parasitized macrophage and release of amastigotes; (8) spread of infection via phagocytosis of released amastigotes or those still in the vacuoles by newly arrived macrophages or scavenging phagocytosis of degenerating cells by multiple newly arrived macrophages. Reservoirs include canines, humans, rodents and other wild animals, for example, sloth in South America. Sandfly stage: (9) ingestion of parasitized macrophages by sand flies after a bloodmeal taken from infected humans or reservoir animals; (10) rupture of the ingested macrophages and release of amastigotes in the gut of sand flies; (11) replication of amastigotes and their differentiation into promastigotes; (12) replication of promastigotes in midgut and insertion of their flagella into microvilli of the gut epithelial cells; (13) replication of those in the Viannia subgenus, for example, Leishmania brasilienisis in the pylorus and ileum of the sand fly hindgut as paramastigotes with broadened flagella attached to the chitinous gut wall via hemi‐desmosomes; (14) forward movement of promastigotes to thoracic midgut as haptomonads with broad flagella attached to the chitinous gut wall; (15) sessile paramastigotes with broad flagella attached to the chitinous wall of stomadeal valve, pharynx and buccal cavity or cibarium; (16) actively motile and infective promastigotes found in the proboscis or mouth part of female sand flies.

Figure 2.

Hypothetical model of host‐parasite interactions depicting Leishmania virulence as reflected in the clinical spectrum of the disease phenotypes seen during the progression of human leishmaniasis. (1) Parasite surface/secreted molecules, collectively referred to as invasins/evasins, allow Leishmania to evade host innate defenses for successful host/host cell invasion; (2) Leishmania pathoantigens vary with different species and thus elicit different host immunopathology, accounting for the spectrum of disease phenotypes seen; (3) Leishmania vaccine molecules, which elicit acquired cell‐mediated immunity to resolve simple cutaneous leishmaniasis of the Eurasian continent spontaneously and mucocutaneous/visceral Leishmaniasis after successful therapeutic intervention.



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Chang, Kwang Poo(May 2012) Leishmaniases. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001954.pub3]