Larvivorous fish misconception — DTM&H MCQ

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HardEntomology and vector controlLarvivorous fish misconceptionDTM&H

A village proposes adding larvivorous fish to household water jars during a dengue outbreak, but most breeding sites are small, disposable containers. What is the most appropriate prophylaxis?

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Correct answer: A — Container removal and covering water storage

Container removal and covering water storage (A) is correct because Aedes aegypti, the dengue vector, breeds preferentially in small, artificial water-holding containers rather than large open water bodies, so source reduction (removing, emptying, or covering these containers) directly eliminates larval habitat. The vignette specifies that most breeding sites are small, disposable containers, which is the classic Aedes ecological niche, not the large, permanent bodies of water suited to biological control with fish. UK travel health guidance on dengue explicitly advises reducing breeding sites around the home by removing stagnant water and rubbish, reflecting the same source reduction principle. Environmental management of this kind is the mainstay of community-level dengue vector control because it is sustainable, low-cost and does not depend on continuous chemical or biological inputs. Why the other options are wrong: B. Distribute tsetse traps: Tsetse flies transmit African trypanosomiasis, not dengue, so tsetse traps have no role in Aedes control. E. Introduce fish to every tyre: Larvivorous fish work in large, stable water containers such as wells or tanks, not in the numerous small, disposable containers described, so this is impractical at scale and does not match the breeding ecology in the stem. D. Treat rivers with molluscicide: Molluscicides target snail intermediate hosts of schistosomiasis, not mosquito larvae, and dengue vectors do not breed in flowing river water. C. Give ivermectin to residents: Ivermectin is used for helminth and ectoparasite infestations (eg onchocerciasis, scabies); it has no established prophylactic role against dengue virus or its mosquito vector. Key point: Match the intervention to the breeding ecology; small disposable container-breeding Aedes requires source reduction (removal or covering), while biological agents like larvivorous fish suit large, fixed water containers.

Reference: NaTHNaC (TravelHealthPro), Dengue factsheet, 2024, https://travelhealthpro.org.uk/factsheet/13/dengue