by Triana Rathads

Created on: April 10, 2009   Last Updated: April 11, 2009

Malaria is caused by a protozoan parasite of the genus Plasmodium, there are three types of malaria: tertian malaria caused by P. vivax and P. ovale, quartan malaria caused by P. malariae, and tropical malaria caused by P. falciparum. The life cycles of all these parasites are essentially the same. There are two main stages in their life cycles; the first is an exogenous sexual phase called sporogony with multiplication in certain Anopheles mosquitoes; and the second is an endogenous asexual phase called schizogony with multiplication in the vertebrate host. The P. falciparum infected blood cells are able to bind to uninfected blood cells which prevents there passage through the spleen; blockage of capillaries causes cerebral malaria and eventually death. The only hosts in the life cycle are humans, with the mosquito as a vector. The parasites live in hepatic cells (liver cells) and erythrocytes (blood cells), the symptoms are fever, shivering, joint pain, headache, anaemia, and a coma.

An infected female mosquito (Anopheles spp.) bites a human, which releases sporozoites into the blood stream. The parasite from mosquito saliva, travels to the human liver within 30 minutes, and sporozoites enter hepatic cells and reproduce asexually. The parasite reproduces rapidly within the liver. Some parasites lay dormant in the liver and become activated years later. Such as in the parasites P. vivax, and P. ovale where the sporozoites differentiate into hypnozoites as well as merozoites, it is thee hypnologists which remain dormant in hepatocytes for considerable periods of time, and the mechanisms of activation remain unknown. The parasites are released into the blood stream in the form of merozoites, which enter red blood cells (erythrocytes), and reproduce further.

Infected red blood cells, burst and infect other blood cells. This cycle reduces the available oxygen and causes fever. Merozoites develop into gametocystes which travel through the blood stream, waiting to be taken up by another female mosquito. Once taken up the gametocysts develop into micro and macrogametes. The microgamete fertilises the macrogametes, which forms a zygote which develops into a ookinete.

Ookinetes enter the midgut wall of the mosquito and develop into an oocyst. The oocysts produce asexual sporozoites. The sporozoites are released and migrate to the lumen of the salivary gland, which makes the mosquito infective. The life cycle of malaria is aided by conflict in many countries, which forces people to live under conditions which encourage close contact with infected individuals, which facilitates the spread of disease.

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