Tsetse fly biology — DTM&H MCQ

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ModerateEntomology and vector controlTsetse fly biologyDTM&H

A cattle-raising area has human African trypanosomiasis and animal wasting disease. The suspected vector gives birth to larvae rather than laying batches of eggs. What is the vector or intermediate host most relevant to this infection?

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Correct answer: B — Glossina tsetse fly

The correct answer is B, Glossina tsetse fly. This vector transmits both human African trypanosomiasis (sleeping sickness) and the animal disease nagana (wasting disease in cattle) caused by related trypanosome species, explaining the mixed human and veterinary picture in the cattle-raising area described. The key discriminating clue in the stem, a vector that gives birth to larvae rather than laying eggs, points specifically to Glossina, which is unusual among medically important dipteran vectors in being larviparous (adenotrophic viviparity), retaining and nourishing a single larva in utero before depositing it directly into soil to pupariate. This biology is well documented in tsetse research and underlies their comparatively low reproductive rate, which is exploited in vector control programmes such as sterile insect technique and targets/traps. No other option shares this larviparous reproductive strategy or this dual human/animal trypanosome transmission pattern. Why the other options are wrong: B Culex mosquito: Culex species lay batches of eggs on water surfaces and transmit filariasis, Japanese encephalitis and West Nile virus, not African trypanosomes. C Phlebotomine sandfly: Sandflies oviposit eggs in organic-rich soil and are vectors of Leishmania species and some arboviruses, not trypanosomes causing nagana or sleeping sickness. D Chrysops deerfly: Chrysops lays egg masses and is the vector of Loa loa (loiasis), a filarial worm, not African trypanosomiasis. E Simulium blackfly: Simulium lays eggs in fast-flowing water and transmits Onchocerca volvulus (river blindness), unrelated to trypanosome transmission. Key point: Glossina tsetse flies are uniquely larviparous among vectors and are the sole transmitters of the trypanosomes causing both human sleeping sickness and animal nagana.

Reference: NaTHNaC/TravelHealthPro, Trypanosomiasis (African Sleeping Sickness), UK national travel health guidance, https://travelhealthpro.org.uk/disease/214/trypanosomiasis