A 7-year-old boy from Bihar presents with prolonged fever, weight loss, hepatosplenomegaly, and darkening of skin (“kala-azar”). The vector responsible is:

Correct option is B

Kala-azar (visceral leishmaniasis) is transmitted by the bite of female Phlebotomus sandfly. India is endemic, especially Bihar.
Explanation of options: (a) ✘ Anopheles transmits malaria, not leishmaniasis. (b) ✔ Correct; female sandfly is the vector of kala-azar. (c) ✘ Culex transmits filariasis, not kala-azar. (d) ✘ Male sandflies do not bite or transmit infection.