Malaria and Anopheles Decline in Hot Summer and Cold Winter

During hot summers and cold winters, there is a decline in the number of malaria cases as well as the population of Anopheles mosquitoes. This is because these extreme weather conditions are not favorable for the survival and reproduction of both the malaria parasites and the mosquito vectors.

Reappearance of Malaria in Humid Warm Conditions

However, with the onset of humid warm conditions, there is a reappearance of malaria. This can be attributed to the presence of mosquito larvae in permanent waters, which serve as breeding grounds for the mosquitoes.

Explanation of the Correct Answer

The correct answer, option D, states that the reappearance of malaria in humid warm conditions is due to mosquito larvae in permanent waters. Let's understand this in detail:

- Mosquito Life Cycle: Mosquitoes, including the Anopheles mosquito that transmits malaria, undergo a complex life cycle that involves four stages: egg, larva, pupa, and adult. The mosquito larvae develop in water bodies, such as stagnant ponds, puddles, or other sources of standing water.

- Permanent Waters: Permanent waters refer to water bodies that persist throughout the year, regardless of the season. These can include lakes, reservoirs, swamps, or even artificial containers that hold water for long periods.

- Mosquito Breeding: Mosquitoes lay their eggs in or near water bodies. These eggs hatch into larvae, which are commonly known as wrigglers. The larvae live in the water and feed on microorganisms and organic matter present in the water.

- Mosquito Larvae and Malaria: The Anopheles mosquito larvae can act as carriers of the malaria parasite. If the larvae are present in permanent waters, they can continue to develop and eventually transform into adult mosquitoes capable of transmitting malaria.

- Humid Warm Conditions: Humid warm conditions provide an ideal environment for the survival and reproduction of mosquitoes, including the Anopheles species. The presence of permanent waters during such conditions allows the mosquito larvae to thrive and complete their life cycle.

- Malaria Transmission: When the adult female Anopheles mosquito feeds on an infected human, it ingests the malaria parasites, called sporozoites, along with the blood. These sporozoites then develop in the mosquito's salivary glands. When the mosquito bites another human, it injects these sporozoites into the bloodstream, initiating a new malaria infection.

Therefore, the presence of mosquito larvae in permanent waters during humid warm conditions provides a suitable environment for the development of Anopheles mosquitoes and the transmission of malaria. This explains why the reappearance of malaria occurs in such conditions.

Option D is correct..