Decontamination of drinking water, fruits, and vegetables would least affect which disease?

• A. Giardiasis
• B. Amebiasis
• C. Filariasis
• D. Ascariasis

Answer: (C)

Decontaminating drinking water and washing fruits and vegetables primarily reduces diseases that are spread by ingesting contaminated water or produce. Protozoan infections like giardiasis and amebiasis are transmitted through cysts in water or on produce, so improving water quality and thorough washing markedly lowers exposure. Filariasis, on the other hand, is transmitted by mosquitoes; its spread depends on the mosquito vector, not on ingestion of contaminated water or food, so such decontamination has little impact on transmission. Ascariasis is mainly a soil-transmitted helminth, with eggs ingested from contaminated soil or produce; while washing produce can help, the main exposure route is soil contact, so decontaminating water and produce is less effective than it is for the water/food–borne protozoa. Thus, the disease least affected by these decontamination measures is filariasis.