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''Plasmodium'', commonly known as the malaria parasite, is a large genus of parasitic protozoa. As with some other genera of clinically important microorganisms, the genus name also yields a common noun; thus species of the genus are known as plasmodia. Infection with plasmodia is known as malaria, a deadly disease widespread in the tropics. The parasite always has two hosts in its life cycle: a Dipteran insect host and a vertebrate host. Sexual reproduction always occurs in the insect definitive host (also known as the disease vector). The life-cycle is very complex, involving a sequence of different stages both in the vector and the vertebrate host. These stages include sporozoites, which are injected by the insect vector into the vertebrate host's blood; latent hypnozoites, which may rest undetected in the liver for up to 30 years; merosomes and merozoites, which infect the red cells (erythrocytes) of the blood; trophozoites, which grow in the red cells, and schizonts, which divide in red blood cells. Schizonts produce merozoites, which leave to infect more red cells. The sexual forms, gametocytes, are taken up by other insect hosts during feeding. Gametocytes develop into gametes in the insect midgut, and then fertilize each other to form motile zygotes, which escape the gut. Zygotes grow into new sporozoites, which move to the insect's salivary glands. Sporozoites are injected into vertebrate hosts during insect feeding, thus completing the cycle of infection. The genus ''Plasmodium'' was first described in 1885. It now contains about 200 species divided into several subgenera; as of 2006 the taxonomy was shifting, and species from other genera are likely to be added to ''Plasmodium''. At least ten species infect humans; other species infect other animals, including birds, reptiles and rodents, while 29 species infect non-human primates. The parasite is thought to have originated from Dinoflagellates, photosynthetic protozoa. The most common forms of human malaria are caused by ''Plasmodium falciparum'', ''P. vivax'', ''P. knowlesi'', and ''P. malariae''. ''P. falciparum'', common in sub-Saharan Africa, and ''P. knowlesi'', common in Southeast Asia, are especially dangerous. ==Taxonomy and host range == The genus ''Plasmodium'' was created in 1885 by Marchiafava and Celli and there are over 200 species recognized. New species continue to be described. , the genus is in need of reorganization as it has been shown that parasites belonging to the genera ''Haemocystis'' and ''Hepatocystis'' appear to be closely related to ''Plasmodium''. It is likely that other species such as ''Haemoproteus meleagridis'' will be included in this genus once it is revised. Host range among the mammalian orders is non uniform. At least 29 species infect non-human primates; rodents outside the tropical parts of Africa are rarely affected; a few species are known to infect bats, porcupines and squirrels; carnivores, insectivores and marsupials are not known to act as hosts. In 1898 Ronald Ross demonstrated the existence of ''Plasmodium'' in the wall of the midgut and salivary glands of a ''Culex'' mosquito. For this discovery he won the Nobel Prize in 1902. However credit must also be given to the Italian professor Giovanni Battista Grassi, who showed that human malaria could only be transmitted by ''Anopheles'' mosquitoes. For some species the vector may not be a mosquito. Mosquitoes of the genera ''Culex'', ''Anopheles'', ''Culiseta'', ''Mansonia'' and ''Aedes'' may act as vectors. The known vectors for human malaria (more than 100 species) belong to the genus ''Anopheles''. Bird malaria is commonly carried by species belonging to the genus ''Culex''. Only female mosquitoes bite. Aside from blood both sexes live on nectar, but one or more blood meals are needed by the female for egg laying, because there is very little protein in nectar. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plasmodium」の詳細全文を読む スポンサード リンク
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