Which of the following is a measure for the control of bilharzia?

Step 1: Analyze the question We need a control measure for bilharzia (schistosomiasis), so we first need to know how the disease spreads.

Step 2: The concept

• Bilharzia is caused by a blood fluke, Schistosoma (a trematode).
• Its life cycle needs an intermediate host, the freshwater snail (Bulinus or Biomphalaria).
• Larvae called cercariae are released by the snails into the water. They penetrate the skin of people who wade, swim, wash or fish in infected water.
• Control therefore targets the snail host, the contaminated water, and human contact with it.

Step 3: Evaluate the options

• A. Cutting low bushes around homes: This removes breeding places for mosquitoes and tsetse flies. It does not help with bilharzia.
• B. Application of molluscicides in water bodies: Molluscicides kill molluscs such as snails. Killing the snail host breaks the life cycle, so this is a valid control measure.
• C. Screening windows and doors with mosquito nets: This prevents mosquito-borne diseases such as malaria. Bilharzia is not spread by mosquitoes.
• D. Application of herbicides in water bodies: Herbicides kill plants. Removing aquatic weeds could indirectly reduce snail habitats, but it is not the direct or standard control measure. The question wants the one that targets the snail.

Step 4: Answer The correct answer is B. Application of molluscicides in water bodies.

Exam tip: Match the vector or host to the control method:

• Mosquito → nets, drain stagnant water
• Tsetse fly → clear bushes
• Snail → molluscicides (mollusc = snail)
• Also avoid contact with infected water and use clean, treated water for bathing and washing.