A trophozoite (G. trope, nourishment + zoon, animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing Plasmodium falciparum and those of the Giardia group. (The complement of the trophozoite state is the thick-walled cyst form.)
They are often different from the cyst stage, which is a protective, dormant form of the protozoa. Trophozoites are often found in the host's body fluids and tissues and in many cases, they are the form of the protozoan that causes disease in the host. (The complement of the trophozoite state is the thick-walled cyst form.) In the protozoan, Entamoeba histolytica it invades the intestinal mucosa of its host, causing dysentery, which aid in the trophozoites traveling to the liver and leading to the production of hepatic abscesses.
Life cycle stages
Trophozoite and cyst stages are shown in the life cycle of Balantidium coli the causative agent of balantidiasis.
In the apicomplexan life cycle the trophozoite undergoes schizogony (asexual reproduction) and develops into a schizont which contains merozoites.
The trophozoite life stage of Giardia colonizes and proliferates in the small intestine. Trophozoites develop during the course of the infection into cysts which is the infectious life stage.