Biology · MU Sofia

42. Leishmania donovani.

Covers Leishmania donovani, the agent of visceral leishmaniasis (Black Fever), placing it among the Leishmania species that cause human disease. It explains the two parasite forms, amastigotes and promastigotes, and their morphology, then compares L. donovani with L. tropica and L. braziliensis by region and symptoms. It closes with the life cycle through the Phlebotomus sandfly vector, from infection and macrophage invasion to reinfection and restart.

Inside: 1 section · 2 labelled pictures · 2 min

Topic 42 of 64 in the MU Sofia syllabus for Biology (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 253 words (2 min of reading).

In this note

  1. Introduction

Introduction

Genus Leishmania

  • Parasite Forms:
  • Amastigotes: Intracellular form found in the vertebrate host.
  • Promastigotes: Extracellular form present in the sandfly vector.
  • Invasion and Transformation: The parasites invade dendritic cells and macrophages in the dermis, transforming into amastigotes after losing their flagella.
  • Species Diversity: Over 20 Leishmania species are responsible for various forms of leishmaniases in humans.

Key Leishmania Species

  • Leishmania Donovani
  • Disease: Causes visceral leishmaniasis, also known as Black Fever.
  • Symptoms: Includes swelling of the liver and spleen.
  • Outcome if Untreated: Typically results in death.
  • Leishmania Tropica
  • Regions Affected: Found in Africa, Europe, and Asia.
  • Symptoms: Characterized by large ulcers and cutaneous lesions.
  • Leishmania Braziliensis
  • Regions Affected: Central and South America.
  • Symptoms: Causes skin lesions similar to L. tropica and mucocutaneous lesions including deeper nasal and oral ulcers.

Transmission and Morphology

  • Vector: The female Phlebotomus sandfly.
  • Hosts: Affects humans, dogs, and rats.
  • Morphology:
  • Amastigote: Oval, non-motile, lacks flagella or cilia.
  • Promastigote: Motile, elongated, contains a nucleus, terminal kinetoplast, and a single flagellum.

Life Cycle of Leishmania

  • Initial Infection: Sandfly takes a blood meal, injecting promastigotes into the skin.
  • Phagocytosis: Promastigotes are phagocytized by macrophages or other mononuclear phagocytic cells.
  • Transformation and Multiplication: Inside these cells, promastigotes transform into amastigotes, multiply, and infect other cells.
  • Reinfection: A sandfly ingests infected macrophages during a blood meal.
  • Metamorphosis in Vector: Amastigotes transform back into promastigotes within the sandfly's gut.
  • Migration and Division: Promastigotes divide in the gut and migrate to the proboscis.
  • Cycle Repeats: The infectious cycle is ready to restart when the sandfly bites another host.

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