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A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. ...
-causing ''
Plasmodium falciparum ''Plasmodium falciparum'' is a unicellular protozoan parasite of humans, and the deadliest species of ''Plasmodium'' that causes malaria in humans. The parasite is transmitted through the bite of a female '' Anopheles'' mosquito and causes the ...
'' and those of the ''
Giardia ''Giardia'' ( or ) is a genus of anaerobic flagellated protozoan parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and ...
'' group. (The complement of the trophozoite state is the thick-walled
cyst A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...
form).


Life cycle stages

Trophozoite and cyst stages are shown in the life cycle of ''
Balantidium coli ''Balantidium coli'' is a parasitic species of ciliate alveolates that causes the disease balantidiasis. It is the only member of the ciliate phylum known to be pathogenic to humans. Morphology ''Balantidium coli'' has two developmental stag ...
'' the causative agent of
balantidiasis Balantidiasis is a protozoan infection caused by infection with '' Balantidium coli''. Symptoms and signs Usually asymptomatic in immunocompetent individuals, but the symptoms of balantidiasis include: * Intermittent diarrhea * Constipation * Vom ...
. In the
apicomplexan life cycle Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
the trophozoite undergoes schizogony (asexual reproduction) and develops into a
schizont Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
which contains merozoites. The trophozoite life stage of ''
Giardia ''Giardia'' ( or ) is a genus of anaerobic flagellated protozoan parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and ...
'' colonizes and proliferates in the small intestine. Trophozoites develop during the course of the infection into cysts which is the infectious life stage.


References

Parasitology {{parasite-stub