Plasmodium
Plasmodium berghei
Plasmodium brasilianum
Plasmodium chabaudi
Plasmodium cynomolgi
Plasmodium falciparum
Plasmodium gallinaceum
Plasmodium knowlesi
Plasmodium lophurae
Plasmodium malariae
Plasmodium ovale
Plasmodium vivax
etc.
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Plasmodium is a genus of parasitic
protozoa, four species of which cause
malaria in humans. Other species attack
birds or
lizards. In
1898 Ronald Ross demonstrated the existence of
Plasmodium in the stomach of the
Anopheles mosquito. For this discovery he won the
Nobel Prize in
1902. However some credit must also be given to the Italian professor, Giovanni Grassi, who showed that human malaria could only be transmitted by
Anopheles mosquitoes.
The four species of
Plasmodium that attack humans are
Plasmodium falciparum (the cause of malignant tertian malaria),
Plasmodium vivax and the much rarer
Plasmodium ovale (the causes of "benign" tertian malaria), and
Plasmodium malariae (the cause of "benign" quartan malaria.)
The life cycle of
Plasmodium is very complex. Starting with the cryptozoite stage hidden in the
liver the
parasite then invades the
red blood cells as ring and amoeboid stages (trophozoites). Active parasites (merozoites) are produced which leave the red blood cells and travel within the blood to invade new red blood cells. After the merozoites infect new red blood cells, eventually the sexual stages (gametocytes) are produced (also in the blood), which are taken up by the female
Anopheles mosquito and form zygotes which split to produce large numbers of tiny
sporozoites. The sporozoites are the infective stage which migrate to the salivary glands of the mosquito where they are injected into the blood of the next host the mosquito bites. The sporozoites move to the liver where they repeat the cycle. The
fever and chills of malaria are caused by the activities of the parasites in the blood breaking down cells and producing toxic materials. Because of the complex life cycle of these parasites it is difficult to develop a
vaccine.
