Sterile insect technique — DTM&H MCQ

Correct answer: B — Glossina species

The correct answer is B, Glossina species (tsetse flies). Tsetse flies are the only cyclical vectors of Trypanosoma brucei causing human sleeping sickness and of T. congolense and T. vivax causing nagana in cattle, making them the biologically plausible single target for a species-specific sterile insect technique (SIT) programme. SIT depends on mass rearing, low mating frequency and slow reproduction of the target insect, criteria Glossina uniquely satisfies among fly vectors, and this approach achieved eradication of Glossina austeni on Unguja Island, Zanzibar. No other fly genus transmits both human and bovine African trypanosomiasis, so only Glossina fits the stem's dual disease description. Why the other options are wrong: C. Stomoxys calcitrans: This is the stable fly, a mechanical (not cyclical) vector of some trypanosomes and other pathogens, but it does not sustain the biological transmission cycle required for HAT or classic nagana and has not been an SIT eradication target for these diseases. D. Chrysops dimidiata: This deerfly transmits Loa loa (loiasis), an entirely different filarial disease, not trypanosomiasis. A. Musca sorbens: This housefly is associated with mechanical transmission of trachoma and diarrhoeal disease via eye and faecal contact, not trypanosome transmission. E. Hippobosca species: These louse flies are ectoparasites of large mammals, implicated in some mechanical pathogen spread but not recognised cyclical vectors of trypanosomiasis, and are not SIT programme targets. Key point: Only Glossina (tsetse) flies are cyclical vectors of both human sleeping sickness and bovine nagana, which is why area-wide SIT campaigns (for example, Glossina austeni eradication on Zanzibar) target this genus specifically.

Reference: IAEA, The Sterile Insect Technique for Control of Tsetse Flies in Africa; and Vreysen MJB, Principles of area-wide integrated tsetse fly control using the sterile insect technique, Med Trop 2001;61(4-5) https://www.iaea.org/sites/default/files/20305482024.pdf