noun, plural: tachyzoites
Apicomplexa is a phylum comprised of protozoans characterized by having a special organelle called an apical complex, and most of them are single-celled, parasitic, and spore-forming. They are intracellular parasites. Their life cycle is comprised of stages where each has a particular cellular variety. Nevertheless, not all members have all the various life stages. Taking for instance the life cycle of Toxoplasma gondii (causative agent of toxoplasmosis), the various cell types in the life cycle of this species includes bradyzoites, tachyzoites, and oocysts. A bradyzoite is a sessile, slow-growing cell type. In latent toxoplasmosis, the bradyzoites form clusters within a cyst (pseudocyst) lodged in muscle and brain tissues of the host. The bradyzoites may give rise to either tachyzoites or gametocytes. The tachyzoites, in comparison with bradyzoites, are relatively faster-growing, actively multiplying, and invasive cell type. Tachyzoites are also motile. They invade cells of almost any cell type. Inside the cell, they multiply until the cell dies and the tachyzoites are released to invade more cells. They divide by endodyogeny and endopolygeny. Certain tachyzoites differentiate into bradyzoites and become tissue cyst mainly in the brain, muscle, and liver tissues of the host.
Word origin: Greek tachys ("fast") + zōon ("animal")