4.10 Managing Water-Related Disease

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Main Content

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1. The Life Cycle of the Malaria Parasite

What is malaria? Malaria is a serious disease that kills hundreds of thousands of people every year, mostly in tropical regions of Africa, Asia, and South America. It is caused by a tiny organism called Plasmodium — this is the malaria parasite (a parasite is a living thing that lives inside another organism and harms it).

Malaria is not spread directly from one person to another. Instead, it needs a carrier — the female Anopheles mosquito. A carrier that spreads a disease without causing disease in itself is called a vector.

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Step-by-step: The Life Cycle of the Malaria Parasite

The life cycle involves two hosts — a human and a mosquito. Here is what happens at each stage:

Stage 1 — Mosquito bites an infected human

• A female Anopheles mosquito feeds on the blood of a person who already has malaria.
• As it sucks blood, it also takes in Plasmodium parasites that are living in that person's blood.

Stage 2 — Inside the mosquito

• The Plasmodium parasites reproduce sexually (they mate and multiply) inside the mosquito's gut and body.
• The parasites eventually move into the mosquito's salivary glands (the glands that produce saliva in the mosquito's mouth).

Stage 3 — Mosquito bites a healthy human

• When the infected mosquito bites a healthy person, it injects saliva into the person's bloodstream (this is how it stops the blood from clotting while it feeds).
• The Plasmodium parasites travel with the saliva into the new human host.

Stage 4 — Inside the human liver

• The parasites first travel to the liver, where they enter liver cells and multiply rapidly (reproduce asexually — without mating, just copying themselves).
• After multiplying, they burst out of the liver cells and enter the red blood cells.

Stage 5 — Inside the red blood cells

• The parasites multiply again inside the red blood cells.
• Eventually, the red blood cells burst open, releasing more parasites into the bloodstream.
• This bursting causes the symptoms of malaria — fever, chills, sweating, headache, and fatigue. The symptoms come in repeated waves because the cells burst in cycles.

Stage 6 — The cycle continues

• Some Plasmodium parasites in the blood develop into a form that can be picked up by another mosquito when it bites the infected person — and the whole cycle starts again.