Malaria Causes

By Dr Ananya Mandal, MD

Malaria is caused by a parasite belonging to the Plasmodium family. The parasite can be spread to humans through the bites of infected mosquitoes. There are numerous types of Plasmodium parasite, but only five types cause malaria in humans. These include:-

Plasmodium falciparum

This type is mainly found in Africa and is common cause of complicated and fatal malarias worldwide

Plasmodium vivax

This is common in Asia and Latin America. The symptoms caused by this type are less severe than Plasmodium falciparum, but it can stay in the liver for up to three years, which can result in relapses and repeat episodes.

Plasmodium ovale

This is relatively uncommon type of malaria usually found in West Africa. This can stay in the liver for years without obvious symptoms.

Plasmodium malariae

This is a rare type of malaria found in Africa

Plasmodium knowlesi

This was initially thought to be same as Plasmodium malariae but was later found to be distinctly different in its course which may be life threatening. It is found rarely and seen in some parts of Southeast Asia.

Malaria spread

The Plasmodium parasite is spread by the female Anopheles mosquitoes. These are night biting mosquitoes that bite between dusk and dawn. The male mosquitoes do not bite and do not feed on human blood like the female mosquitoes do. Once the mosquito bites a person infected with malaria, it can also become infected and spread the parasite on to others.

In the mosquitoes’ gut the parasite develops into sporozoite forms. These sporozoites remain in the mosquito saliva from where they infect the human.

The sporozoites enter the blood stream and go into the liver. The infection develops in the liver and the multiplied parasites re-enter the bloodstream. The sporozoites then form merozoites. This time they infect the red blood cells.

In certain species the sporozoites may lie dormant in the liver (when they are known as hypnozoites). The parasites grow and multiply in the red blood cells. At regular intervals of around 48 to 72 hours the infected blood cells burst, releasing more parasites into the blood. Each time they burst there is a bout of fever, chills and sweating.

The parasite remains is blood in the form of gametocytes to be taken up by a non-infected mosquito. In the mosquito’s gut the gametozytes fuse to form zygotes or sporozoites (sexual reproduction). The mosquito then transmits it to another individual. Thus the life cycle of the Plasmodium parasite is complete.

Malaria can also affect pregnant women living in high risk areas. There is a high risk of complications in this situation. The risk of premature birth, stillbirth and miscarriage also rises.

Reviewed by April Cashin-Garbutt, BA Hons (Cantab)

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