NCERT · Class 12 · Biology · Human Health and DiseasesDescribe the complete life cycle of the malarial parasite (Plasmodium) in the human host and female Anopheles mosquito. Include the symptoms and preventive measures for malaria.

Life Cycle of Plasmodium

Plasmodium is a digenetic endoparasite requiring two hosts to complete its life cycle: humans (secondary host/asexual cycle) and female Anopheles mosquitoes (primary host/sexual cycle).

1. Human Phase (Asexual Reproduction / Schizogony):

1. Infection: When an infected female Anopheles mosquito bites a human, it injects the infectious stage of the parasite called sporozoites along with its saliva into the bloodstream.
2. Liver Stage (Exo-erythrocytic cycle): Sporozoites reach the liver cells via blood, multiply asexually inside hepatic cells, causing them to burst open and release merozoites into the blood.
3. RBC Stage (Erythrocytic cycle): Merozoites enter Red Blood Cells (RBCs) and multiply asexually. They periodically rupture the RBCs, releasing toxins called haemozoin along with new merozoites.
4. Gametocyte Formation: Some merozoites inside RBCs differentiate into sexual stages called gametocytes (male microgametocytes and female macrogametocytes).

2. Mosquito Phase (Sexual Reproduction / Sporogony):

1. Uptake: When a female Anopheles mosquito bites an infected human, it ingests gametocytes along with the blood meal.
2. Fertilization and Development: Fertilization between male and female gametes occurs in the mosquito's midgut to form a zygote (ookinete).
3. Sporozoite Formation: The zygote develops into an oocyst on the outer gut wall, undergoes meiotic division to form thousands of sporozoites.
4. Migration: Sporozoites burst from the oocyst and migrate to the mosquito's salivary glands, making the mosquito infective.

Symptoms of Malaria:

• Recurrent high fever accompanied by severe chills and shivering occurring every 3–4 days (due to the release of haemozoin).
• Profuse sweating, severe headache, muscular pain, nausea, and anemia due to destruction of RBCs.

Preventive Measures:

• Control mosquito population using insecticides (e.g., DDT) and biological control like introducing Gambusia fish in ponds to feed on mosquito larvae.
• Avoid stagnation of water around residential areas.
• Use mosquito nets, repellents, and wire mesh on doors and windows to prevent mosquito bites.