Aedes mosquito — DTM&H MCQ

Correct answer: A — Aedes aegypti mosquito

The correct answer is A, Aedes aegypti mosquito. Dengue virus is transmitted by female Aedes aegypti mosquitoes, which are day-biting insects most active in the early morning and late afternoon before dusk, exactly matching the exposure pattern described. This mosquito breeds in small collections of clean water around human dwellings and is highly domesticated, explaining its dominance in urban outbreaks such as in Bangkok. The clinical triad of fever, retro-orbital pain and thrombocytopenia is classic for dengue, and confirming the correct vector underpins advice on daytime bite avoidance and larval source reduction rather than nocturnal protection measures used for malaria. Why the other options are wrong: E. Culex quinquefasciatus mosquito: this is the principal vector of lymphatic filariasis and some forms of viral encephalitis (eg Japanese encephalitis vectors are Culex species), not dengue, and it typically bites at night rather than during the day. D. Simulium blackfly: this is the vector for onchocerciasis (river blindness), transmitted near fast flowing rivers, and has no role in dengue transmission. B. Anopheles gambiae mosquito: this is the principal African vector of malaria, feeding predominantly at night (dusk to dawn), which does not fit the daytime biting history given. C. Phlebotomus sandfly: this transmits leishmaniasis (and sandfly fever viruses), bites at dusk and night, and is unrelated to dengue. Key point: Dengue is transmitted by the day-biting Aedes aegypti mosquito, with peak activity in early morning and late afternoon, distinguishing it from the night-biting vectors of malaria, filariasis and leishmaniasis.

Reference: NaTHNaC (National Travel Health Network and Centre), TravelHealthPro, Dengue factsheet: Aedes aegypti mosquitoes are most active during daylight hours, feeding from dawn to dusk. https://travelhealthpro.org.uk/factsheet/13/dengue