What would be the most effective method of reducing the incidence of blood flukes in a human population?

By the use of uncontaminated water

Explanation:

Blood flukes are flatworms that are parasitic in nature. These are also called schistosomes.

If we consider the mode of transmission of the parasites to humans, we find that their transmission occurs in the following conditions -

Thus it becomes clear that contaminated water is the main source of infection of blood flukes so using uncontaminated water and avoiding to be in contact with contaminated water will reduce the incidence of blood flukes in human population.

it would lead to upper respiratory infections and pneumonia.