Sporozoen

Sporozoa (Sporozoen) is a traditional grouping of parasitic protozoa within the phylum Apicomplexa. They are characterized by complex life cycles that produce sporozoites, the infective forms that invade host tissues. In modern classifications, many organisms once called sporozoa are placed in Apicomplexa, and the term is used mainly as a historical or descriptive reference.

Sporozoa are intracellular parasites characterized by an apical complex at the cell front, including secretory organelles such as micronemes and rhoptries used to attach to and invade host cells. After infection, they replicate by asexual multiplication (often by schizogony) in the host tissue, producing many merozoites. Sexual development can occur in a definitive host or vector, producing cysts or oocysts that release new infective sporozoites.

Many species require two or more hosts. The classic example is Plasmodium, where sporozoites transmitted by Anopheles mosquitoes infect liver cells and then red blood cells, with sexual stages in the mosquito. Toxoplasma gondii alternates between felines (definitive hosts) and a wide range of intermediate hosts; infection forms include tachyzoites and tissue cysts. Other genera include Cryptosporidium, Eimeria, Babesia, and Theileria.

Sporozoan parasites cause malaria, toxoplasmosis, cryptosporidiosis, coccidiosis, babesiosis, and theileriosis, among others. They are studied for their invasion strategies, host cell interactions, and development of antiparasitic therapies.