Anopheles mosquito transmission — DTM&H MCQ

Correct answer: A — Female Anopheles mosquito, typically night-biting

The correct answer is A, female Anopheles mosquito, typically night-biting. Malaria is transmitted to humans through the bite of an infected female Anopheles mosquito, and Anopheles species are generally active at dawn, dusk and through the night rather than in full daylight, which explains why the student did not notice daytime bites. Only the female takes a blood meal (needed for egg development), so the sporozoite-laden salivary secretions are injected during her feeding, making her the obligate vector and humans the intermediate host in the Plasmodium life cycle. This nocturnal/crepuscular feeding pattern is precisely why bite-avoidance advice for travellers emphasises repellents, long sleeves and insecticide-treated nets from dusk to dawn. The stem's clue of fieldwork in a rural, endemic area with no daytime bites strongly points to a night-active Anopheles vector rather than a day-biting species. Why the other options are wrong: B. Glossina tsetse fly, typically daytime-biting: Glossina transmits African trypanosomiasis (sleeping sickness), not malaria, and tsetse flies characteristically bite during the day, which is the opposite ecological pattern from what caused this infection. C. Male Culex mosquito, typically night-biting: male mosquitoes of any genus do not blood-feed at all (they feed on nectar), and Culex species are vectors for viruses such as West Nile and filariasis, not Plasmodium. D. Female Aedes mosquito, typically day-biting: Aedes species are the vectors for dengue, chikungunya, Zika and yellow fever, and are classically day-biting, but they are not competent hosts for human Plasmodium species. E. Phlebotomine sandfly, typically dusk-biting: sandflies transmit Leishmania and are dusk/night active, but they are unrelated to malaria transmission. Key point: Malaria is transmitted only by the bite of a blood-feeding female Anopheles mosquito, which typically feeds from dusk through to dawn, so absence of daytime bites does not exclude exposure.

Reference: NaTHNaC (TravelHealthPro), Malaria factsheet: 'Malaria is transmitted to humans through the bite of an infected female Anopheles mosquito', https://travelhealthpro.org.uk/factsheet/52/malaria