Final answer:
The least effective method to reduce the incidence of lymphatic filariasis suggested by the passage is vaccination against Wolbachia since this method does not directly address the filtration and eradication of the disease or destruction of the infective mosquito vector. The correct option is D.
Step-by-step explanation:
The passage suggests that the least effective method to reduce the incidence of lymphatic filariasis would likely be vaccination against Wolbachia. This is because Wolbachia are bacteria that live symbiotically within the worms causing lymphatic filariasis and do not directly contribute to spreading the infection.
Mass treatments with diethylcarbamazine (DEC) and doxycycline target the disease more directly. DEC treats the infection by targeting the adult worms, while doxycycline targets the Wolbachia bacteria inside the worms, which is essential for worm fertility and survival.
On the other hand, mass spraying with DDT could be a viable option as it targets the mosquitoes that spread the disease, however, it has several drawbacks regarding its persistence in the environment and potential toxicity. Option D. is the correct one.