Which stage of Leishmania donovani is responsible for transmission to a human host during the bite of a sandfly (Phlebotomus), and in which part of the sandfly gut does it develop?

• A Amastigote injected from the midgut
• B Promastigote injected from the proboscis after developing in the hindgut
• C Promastigote (metacyclic, infective form) deposited in the skin after developing in the midgut of the sandfly ✓
• D Epimastigote injected from the salivary glands

Explanation

When a sandfly ingests amastigotes from an infected host, they transform into promastigotes (flagellated form) in the midgut. The infective metacyclic promastigotes migrate anteriorly to the proboscis and are regurgitated into the skin during feeding. They are phagocytosed by macrophages and transform back into non-flagellated amastigotes within phagolysosomes — this is the intracellular stage that multiplies and causes visceral leishmaniasis (kala-azar). Epimastigotes are characteristic of Trypanosoma cruzi life cycle in the insect gut, not Leishmania.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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