apikompleksit

Apikompleksit (Finnish for Apicomplexa) are a diverse phylum of obligate intracellular parasites that infect a wide range of animals. They are characterized by an apical complex, a specialized set of organelles at the cell apex that facilitates invasion of host cells. The life cycles are typically complex and involve both sexual and asexual stages, often with alternating hosts. In many species, sporozoites released from oocysts initiate infection; subsequent asexual replication, called schizogony, produces merozoites that invade additional cells. Some genera undergo further differentiation into stages such as gametocytes that give rise to new oocysts through sexual reproduction.

Most apicomplexans possess a non-photosynthetic plastid, the apicoplast, derived from secondary endosymbiosis. The apicoplast is essential for several metabolic pathways and is a target for certain antimicrobial drugs.

Ecology and disease: Apicomplexans inhabit a broad spectrum of hosts, including humans. Several species are major pathogens, such as Plasmodium (malaria), Toxoplasma gondii (toxoplasmosis), Cryptosporidium (cryptosporidiosis), and Eimeria (coccidiosis in animals). Others infect invertebrates or serve as parasites of vertebrates with vector-borne transmission (mosquitoes, ticks).

Taxonomy and evolution: Apicomplexa is a phylum within Alveolata; members are characterized by the apical complex and their intracellular parasitism. The group is considered monophyletic based on molecular data and includes many medically and economically important genera.