Tsetse fly transmission — DTM&H MCQ

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ModerateEntomology and vector controlTsetse fly transmissionDTM&H

A mobile clinic sees several patients with fever and lymphadenopathy near a riverine forest in South Sudan. Local people report painful bites from large flies, and microscopy later confirms African trypanosomes. Which vector is responsible?

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Correct answer: E — Glossina species

The correct answer is E, Glossina species. African trypanosomiasis (sleeping sickness) is transmitted exclusively by tsetse flies of the genus Glossina, large, robust flies found in riverine and woodland habitats across sub-Saharan Africa, including South Sudan. Their bite is characteristically painful, unlike the comparatively silent probing of mosquitoes, and this clinical clue in the stem (painful bites from large flies near riverine forest) is a classic exam pointer to tsetse exposure. Tsetse flies acquire trypomastigotes when feeding on an infected host and inoculate metacyclic forms at subsequent bites, producing the local chancre, fever and lymphadenopathy (including the posterior cervical Winterbottom's sign) seen in early disease. NaTHNaC (TravelHealthPro) confirms that African trypanosomiasis is spread specifically by the bite of the tsetse fly, with prevention centred on avoiding fly bites in endemic riverine and savannah zones. Why the other options are wrong: D. Aedes species: these mosquitoes transmit arboviral infections such as dengue, yellow fever and chikungunya, not protozoan trypanosomes, and their bite is a typical painless mosquito probe rather than the sharp bite described. C. Anopheles species: this mosquito genus is the vector for malaria (Plasmodium species), transmitted by a painless nocturnal bite, and has no role in trypanosome transmission. A. Culex species: these mosquitoes transmit lymphatic filariasis and certain arboviruses (e.g. West Nile virus, Japanese encephalitis), again via a painless bite, not African trypanosomiasis. B. Pediculus humanus: the body louse transmits epidemic typhus and louse-borne relapsing fever through crushing/scratching of infected lice into skin, not a biting fly mechanism, and is unrelated to trypanosomiasis. Key point: a painful bite from a large fly in riverine African habitat, followed by fever and lymphadenopathy with trypanosomes on microscopy, points to tsetse fly (Glossina) transmitted African trypanosomiasis.

Reference: NaTHNaC (TravelHealthPro), 'Trypanosomiasis' clinical update, https://travelhealthpro.org.uk/disease/214/trypanosomiasis