Malaria – a growing threat
Box 1 | Life cycle of malarial parasite
When an uninfected female Anopheles mosquito bites an infected person, the mosquito takes up parasites in her meal of blood. Once they are safely inside the mosquito, some of these parasites reproduce sexually in the mosquito’s gut. The parasites then travel to the salivary glands of the mosquito where they mature into sporozoites. At the next meal, the mosquito injects a small amount of saliva into her victim to stop the blood clotting, and the sporozoites are passed into a new host. The sporozoites are carried along in the blood of the new host until they reach the liver.
In the host's liver cells the parasite multiplies repeatedly. After about 5 days there are in the order of 40,000 new parasites, called merozoites. At this stage, the liver cell bursts and the merozoites attack red blood cells. In the red blood cells, the parasite divides again, forming about 16 new merozoites which are released to invade new red cells. From time to time, some merozoites form gametocytes. These can be taken up by a mosquito with a blood meal.
- Malarial parasites mature into sporozoites in the salivary glands of a mosquito and enter a human when the mosquito bites
- Sporozoites invade liver cells and reproduce asexually many times, forming large numbers of merozoites.
- The infected liver cells burst, releasing merozoites.
- Merozoites invade red blood cells and continue to reproduce asexually. Each red blood cell produces an average of 16 to 20 merozoites. Occasionally 32 merozoites are seen. This is because the red blood cell was originally infected with two parasites.
- Infected red blood cells rupture and release the parasites and the toxins that
cause fever and chills.
- Some of the parasites are able to form gametocytes.
- A female Anopheles mosquito picks up gametocytes when she bites an infected person. The gametocytes become gametes. Sexual reproduction of the parasite occurs in the mosquito’s gut.
Boxes
Box 2. Controlling malaria
Box 3. Antimalaria vaccine
Box 4. Australian research
Related sites
Malaria (Department of Medical Entomology, University of Sydney, Australia)
Biology of Plasmodium parasites and Anopheles mosquitos (Walter and Eliza Hall Institute, Australia) WEHI-TV – the infection pathway of the malaria parasite (Walter and Eliza Hall Institute, Australia) (Requires Quicktime)
From mosquito to microscope: Research on malaria at the Advanced Light Source (Lawrence Berkeley National Laboratory, USA)
Page updated January 2012.