Leishmania vector — DTM&H MCQ

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ModerateProtozoal infectionsLeishmania vectorDTM&H

A clinic in Bihar sees several patients with fever, weight loss, splenomegaly and pancytopenia. Houses have cracks in mud walls and biting insects are active at dusk. What is the vector or intermediate host most relevant to this infection?

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Correct answer: A — Female phlebotomine sandfly

The correct answer is A, female phlebotomine sandfly. The vignette describes classic visceral leishmaniasis (kala-azar) from the Indian subcontinent: chronic fever, weight loss, massive splenomegaly and pancytopenia (from hypersplenism and marrow infiltration) in a patient from Bihar, the historical epicentre of the disease. Cracks in mud walls provide daytime resting sites for the sandfly Phlebotomus argentipes, and its dusk-to-night biting activity matches the exposure described. Female phlebotomine sandflies transmit Leishmania donovani, the causative protozoan, which infects the reticuloendothelial system and produces this exact triad. This vector-habitat link (peridomestic mud dwellings, cracked walls, dusk biting) is a well-recognised discriminator in UK tropical medicine teaching for anthroponotic visceral leishmaniasis in Bihar. Why the other options are wrong: D. Triatomine bug: transmits Trypanosoma cruzi (Chagas disease), restricted to the Americas, not South Asia, and causes cardiomyopathy or megacolon rather than pancytopenia with splenomegaly. B. Simulium blackfly: transmits Onchocerca volvulus (onchocerciasis), causing skin and eye disease, breeds near fast-flowing rivers, not linked to mud wall cracks or pancytopenia. E. Female Anopheles mosquito: transmits malaria, which can cause fever and splenomegaly but typically presents with a cyclical pattern and haemolysis rather than pancytopenia, and mosquitoes are not associated with wall cracks. C. Glossina tsetse fly: transmits African trypanosomiasis, geographically confined to sub-Saharan Africa and associated with riverine or savannah habitats, not Bihar. Key point: In an Indian subcontinent patient with fever, splenomegaly, weight loss and pancytopenia plus cracked mud walls and dusk-biting insects, think visceral leishmaniasis transmitted by the female phlebotomine sandfly.

Reference: NaTHNaC (National Travel Health Network and Centre), TravelHealthPro: Leishmaniasis factsheet, https://travelhealthpro.org.uk/disease/103/leishmaniasis