Question

Assertion : Malaria spreads rapidly in areas having stagnant water.
Reason : Fishes like Gambusia are introduced into ponds to control the spread of malaria.

Answer 1

Malaria is a protozoan disease caused by the Plasmodium sp. and transmitted through the bite of the female Anopheles mosquito. This disease is characterised by recurring fevers, chills, headache, muscle pain, vomiting, etc. The Plasmodium parasite completes its life cycle in two different hosts, i.e, humans and the female Anopheles mosquito.

The mature infective stages of Plasmodium infest the salivary glands of the mosquito. These enter the human bloodstream when the female Anopheles mosquito bites an individual and injects its saliva (containing anticoagulants) into the bloodstream to prevent clotting.

Different developmental forms of the parasite within the human body infects the liver cells and red blood cells to complete the asexual multiplication phase of its life cycle. In some of the infected blood cells sexual forms of the parasite known as gametocytes are formed. These circulate in the bloodstream, upon release, are picked up by the female Anopheles mosquito when it sucks blood from an infected person.

Malaria is characterised by recurring fevers, chills, bodyache, etc. Every time an RBC ruptures, a toxin named hemozoin is released which is composed of waste products of the parasite along with the heme (iron porphyrin ring) of haemoglobin. Haemozoin immediately triggers the immune response of the body which results in fevers and chills.

One of the hosts of Plasmodium is the female Anopheles mosquito. The female Anopheles mosquito lays eggs in stagnant water. Thus areas with stagnant water in ditches, puddles, open drains, etc. are breeding grounds for the mosquito. Elimination of water stagnation is one of the most effective ways to fight the spread of malaria.

For controlling the growth of the mosquitoes in big stagnant water bodies such as ponds or lakes, fishes such as Gambusia are introduced because these fishes feed on the mosquito larvae.


Hence, both assertion and reason are true but the reason is not the correct explanation for the assertion.