Zoites

Zoites are motile stages of certain protozoan parasites, used to describe the actively moving life forms that enable infection and dissemination. The term derives from Greek zoe, life, with the suffix -ite, and is not a taxonomic category but a descriptive label for invading or propagating stages found in diverse lineages, especially the phylum Apicomplexa and some microsporidia. Zoites arise during various reproductive cycles and are typically adapted for cell invasion, survival within hosts, or transmission between hosts.

Common forms of zoites include sporozoites, merozoites, tachyzoites, and bradyzoites. Sporozoites are usually the initial infective forms produced by sporogony in oocysts and are transmitted by vectors such as mosquitoes; after entering a host, they invade cells and develop into other life stages. Merozoites result from asexual replication within host cells and invade additional cells, contributing to disease progression in infections like malaria. Tachyzoites are rapidly dividing zoites seen during the acute phase of certain infections, such as toxoplasmosis, while bradyzoites are slow-growing, encysted forms that persist in tissues as latent infections.

Lifecycle transitions often involve shifts between invasion, replication, and persistence. For example, in malaria, sporozoites infect liver cells and later merozoites emerge to infect red blood cells; in toxoplasmosis, tachyzoites disseminate quickly and can convert to bradyzoites within tissue cysts. Zoites can vary morphologically across species but share the functional trait of active motility and host cell invasion.

Clinical relevance centers on the detection and study of zoites in blood, tissue, or vectors, which informs diagnosis and treatment of diseases such as malaria and toxoplasmosis.