Plasmodium

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 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.

Plasmodium (life cycle)

A plasmodium is a living structure of cytoplasm that contains many nuclei, rather than being divided into individual cells each with a single nucleus.

Plasmodia are best known from slime molds, but are also found in parasitic Cnidospora, and some algae such as the Chlorarachniophyta.

Structure

A plasmodium is an amoeboid, multinucleate and naked mass of cytoplasm that contains many diploid nuclei. The resulting structure, a coenocyte, is created by many nuclear divisions without the process of cytokinesis which in other organisms pulls newly-divided cells apart.

Taxonomic distribution

The term plasmodium, introduced by Leon Cienkowski, usually refers to the feeding stage of slime molds; these are macroscopic myxomycetes.

The multinucleate developmental stages of some intracellular parasites, namely Microsporidia (now in Fungi) and Myxosporidia (now in Cnidaria), former cnidosporans, are also sometimes called plasmodia.

Similarly, in Rhizaria, the ameboid, multinucleate protoplasts of some Cercozoan algae, e.g. Chlorarachniophyta, are called plasmodia. These lack cell walls; the syncytia are created by cell fusion. Some plasmodiophorids and haplosporidians are other multinucleated rhizarians.