## Epidemiology and Transmission of Kala-azar ### Vector and Transmission **Key Point:** Leishmania donovani is transmitted exclusively by the bite of infected female Phlebotomus sand flies, NOT by mosquitoes. **High-Yield:** In the Indian subcontinent (particularly Bihar, Jharkhand, and West Bengal), the primary vector is *Phlebotomus argentipes*, a nocturnal sand fly that feeds indoors and outdoors. ### Reservoir Hosts **Clinical Pearl:** In the Indian subcontinent, humans are the only significant reservoir host. In Africa and the Mediterranean region, dogs and other animals may serve as reservoirs, but this is NOT the case in India. ### Transmission Mechanism The female sand fly requires a blood meal for egg production. During feeding: 1. Promastigotes are inoculated into the dermis 2. They are phagocytosed by macrophages 3. They transform into amastigotes within the macrophage cytoplasm 4. Intracellular multiplication occurs ### Why Option 4 is Incorrect Mosquitoes play no role in the transmission of kala-azar. This is a common misconception among students who conflate leishmaniasis with other vector-borne diseases like malaria or dengue. Phlebotomus sand flies are the sole vectors. **Mnemonic:** **SAND** = **S**and fly, **A**mastigotes, **N**octurnal, **D**onovani
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