Plasmodium
| Plasmodium | |
|---|---|
 |
|
| False-colored electron micrograph of a Plasmodium sp. sporozoite. | |
| Scientific classification | |
| (unranked): | SAR |
| (unranked): | Alveolata |
| Phylum: | Apicomplexa |
| Class: | Aconoidasida |
| Order: | Haemosporida |
| Family: | Plasmodiidae |
| Genus: |
Plasmodium Marchiafava & Celli, 1885 |
| Species | |
Plasmodium is a genus of parasitic alveolates, many of which cause malaria in their hosts. 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, making it the definitive host.
The life-cycles of Plasmodium species involve several different stages both in the insect and the vertebrate host. These stages include sporozoites, which are injected by the insect vector into the vertebrate host's blood. Sporozoites infect the host liver, giving rise to merozoites and (in some species) hypnozoites. These move into the blood where they infect red blood cells. In the red blood cells, the parasites can either form more merozoites to infect more red blood cells, or produce which are taken up by insects which feed on the vertebrate host. In the insect host, gametocytes merge to sexually reproduce. After sexual reproduction, parasites grow into new sporozoites, which move to the insect's salivary glands, from which they can infect a vertebrate host bitten by the insect.
The genus Plasmodium was first described in 1885. It now contains about 200 species, which are spread across the world where both the insect and vertebrate hosts are present. Five species regularly infect humans, while many others infect birds, reptiles, rodents, and various primates.
Plasmodia were first identified when Charles Louis Alphonse Laveran described parasites in the blood of malaria patients in 1880. He named the parasite Oscillaria malariae. The fact that several species may be involved in causing different forms of malaria was first recognized by Camillo Golgi in 1886. Soon thereafter, Giovanni Batista Grassi and Raimondo Filetti named the parasites causing two different types of human malaria Plasmodium vivax and Plasmodium malariae. In 1897, William Welch identified and named Plasmodium falciparum. This was followed by the recognition of the other two species of Plasmodium which infect humans: Plasmodium ovale (1922) and Plasmodium knowlesi (identified in long-tailed macaques in 1931; in humans in 1965). The contribution of insect hosts to the Plasmodium life cycle was described in 1897 by Ronald Ross and in 1899 by Giovanni Batista Grassi, Amico Bignami and Giuseppe Bastianelli.
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