Life Cycle of Plasmodium
பிளாஸ்மோடியத்தின் வாழ்க்கைச் சுழற்சி
The female Anopheles is not the cause of malaria; she is merely the vector. The true pathogen is the protozoan Plasmodium, which undergoes complex alternation of generations between two hosts. Do not confuse the vector with the parasite in your exam paper.
The idea
Plasmodium enters the human body as sporozoites through the bite of an infected female Anopheles mosquito. The parasites multiply within the liver cells and subsequently attack the red blood cells, causing their rupture. This rupture releases a toxic substance called haemozoin, which is responsible for the characteristic chill and high fever recurring every 3 to 4 days.
Why it matters
Complex life cycles allow parasites to utilize different environments for different developmental stages, increasing their chances of survival and transmission.
NEET lens
NEET focuses on the sequence: Sporozoite -> Liver -> RBC -> Haemozoin. Memorize that the infective stage for humans is the sporozoite, while the gametocytes are the stage that enters the mosquito. Watch for questions swapping the hosts or the specific stages in each host; this is a high-yield area.
Clinical significance
The cyclic release of haemozoin is the clinical hallmark of malaria. If the liver stage is not controlled, the parasite load in the blood increases exponentially, leading to severe anaemia and potential organ failure. Understanding this cycle is critical for diagnosing the specific species of Plasmodium involved.
Introduction
Malaria is caused by Plasmodium (P. vivax, P. malariae, P. falciparum). Its life cycle needs two hosts — humans and the female Anopheles mosquito.
Core concept
Stages: (1) An infected female Anopheles bites a person and injects sporozoites (the infective stage). (2) Sporozoites reach the liver; parasites multiply asexually within liver cells. (3) They then attack red blood cells, multiply there and cause their rupture; this releases a toxic substance, haemozoin, which causes the chill and high fever recurring every three to four days. (4) In RBCs, gametocytes (sexual stages) develop. (5) A female Anopheles biting an infected person takes up gametocytes; fertilisation and development take place in the mosquito's stomach (gut). (6) Sporozoites form and are stored in the mosquito's salivary glands, ready to be injected into the next person. Humans are the intermediate host (asexual reproduction); the mosquito is the definitive host (sexual reproduction).
Go deeper
Plasmodium falciparum causes malignant malaria, the most serious and sometimes fatal form. Haemozoin release when infected RBCs rupture is what causes the periodic fever.
From Class 10
Malaria spreads through mosquito bites. The parasite lives first in our liver, then in red blood cells, before going back into a mosquito.