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Cellular structure of a typical, generalised Apicomplexan: 1-polar ring, 2-conoid, 3-micronemes, 4-rhoptries, 5-nucleus, 6-nucleolus, 7-mitochondria, 8-posterior ring, 9-alveoli, 10-golgi apparatus, 11-micropore.

Apicomplexans, a group of intracellular parasites, have life cycle stages evolved to allow them to survive the wide variety of environments they are exposed to during their complex life cycle.^[1] Each stage in the life cycle of an apicomplexan organism is typified by a cellular variety with a distinct morphology and biochemistry.

Not all apicomplexa develop all the following cellular varieties and division methods. This presentation is intended as an outline of a hypothetical generalised apicomplexan organism.

Methods of asexual replication[edit]

Glossary of cell types[edit]

An ookinete (motile), a sporozoite (motile) and a merozoite (non-motile) of Plasmodium falciparum.

Infectious stages[edit]

A sporozoite (G. sporos, seed + zōon, animal) is the cell form that infects new hosts. In Plasmodium, for instance, the sporozoites are cells that develop in the mosquito's salivary glands, leave the mosquito during a blood meal, and enter liver cells (hepatocytes) where they multiply. Cells infected with sporozoites eventually burst, releasing merozoites into the bloodstream.^[7] Sporozoites are motile and they move by gliding.

A merozoite (G. meros, part [of a series], +zōon, animal) is the result of merogony that takes place within a host cell. In coccidiosis, merozoites form the first phase of the internal life cycle of coccidian. In the case of Plasmodium, merozoites infect red blood cells and then rapidly reproduce asexually. The red blood cell host is destroyed by this process, which releases many new merozoites that go on to find new blood-borne hosts. Merozoites are non-motile.

A gametocyte (G. gametēs, partner + kytos, hollow) is a name given to a parasite's gamete-forming cells. A male gametocyte divides to give many flagellated microgametes, whereas the female gametocyte differentiates to a macrogamete.^[8]

An ookinete (G. ōon, egg + kinētos, motile) is a fertilised zygote capable of moving spontaneously. It penetrates epithelial cells lining the midgut of mosquitos to form a thick-walled structure known as an oocyst under the mosquito's outer gut lining.^[9] Ookinetes are motile and they move by gliding.

A trophozoite (G. trophē, nourishment + zōon, animal) is the activated, intracellular feeding stage in the apicomplexan life cycle. After gorging itself on its host, the trophozoite undergoes schizogony and develops into a schizont, later releasing merozoites.

A bradyzoite (G. bradys, slow + zōon, animal) is a sessile, slow-growing form of zoonotic microorganisms such as Toxoplasma gondii, among others responsible for parasitic infections. In chronic (latent) toxoplasmosis, bradyzoite microscopically presents as clusters enclosed by an irregular crescent-shaped wall (a pseudocyst), in infected muscle and brain tissues.

A tachyzoite (G. tachys, fast + zōon, animal), contrasting with a bradyzoite, is a form typified by rapid growth and replication. Tachyzoites are motile forms of coccidians that form tissue cysts, such as Toxoplasma and Sarcocystis. Typically infecting cellular vacuoles, tachyzoites divide by endodyogeny and endopolygeny.

An oocyst (G. ōon, egg + kystis, bladder) is a hardy, thick-walled spore able to survive for lengthy periods outside a host. The zygote develops within the spore, which acts to protect it during transfer to new hosts. Organisms that create oocysts include Plasmodium, Cryptosporidium and Toxoplasma.

Lifecycle of the Babesia parasite
Lifecycle of the Eimeria parasite
Erythrocytic lifecycle of the Plasmodium parasite
Lifecycle of the Toxoplasma parasite

References[edit]

^ Jadwiga Grabda (1991). Marine fish parasitology: an outline. VCH. p. 8. ISBN 0-89573-823-6.
^ Yoshinori Tanada, Harry K. Kaya (1993). Insect pathology. Gulf Professional Publishing. ISBN 978-0-12-683255-6.
^ "Schizogony definition". MSN Encarta. Retrieved 2009-12-11.
^ Herwaldt et al.; Persing, DH; Précigout, EA; Goff, WL; Mathiesen, DA; Taylor, PW; Eberhard, ML; Gorenflot, AF (1 April 1996). "A Fatal Case of Babesiosis in Missouri: Identification of Another Piroplasm That Infects Humans". Annals of Internal Medicine 124 (7): 643–650. doi:10.1059/0003-4819-124-7-199604010-00004. PMID 8607592. Retrieved 2009-12-11.
^ Zhou et al.; Liu, Q.; Wongsrichanalai, C.; Suwonkerd, W.; Panart, K.; Prajakwong, S.; Pensiri, A.; Kimura, M. et al. (6 January 2002). "High prevalence of Plasmodium malariae and Plasmodium ovale in malaria patients along the Thai-Myanmar border, as revealed by acridine orange staining and PCR-based diagnoses". Tropical Medicine & International Health 3 (4): 304–312. doi:10.1046/j.1365-3156.1998.00223.x. Retrieved 2009-12-11. |displayauthors= suggested (help)
^ ^a ^b James Desmond Smyth, Derek Wakelin (1994). Introduction to animal parasitology (3 ed.). Cambridge University Press. pp. 101–102. ISBN 0-521-42811-4.
^ "Malaria - Life Cycle Of Plasmodium.swf". esnips. Archived from the original on 21 November 2009. Retrieved 2009-12-11.
^ Sinden, R. E.; Talman, A.; Marques, S. R.; Wass, M. N.; Sternberg, M. J. E. (2010). "The flagellum in malarial parasites". Current Opinion in Microbiology 13 (4): 491–500. doi:10.1016/j.mib.2010.05.016. PMID 20566299. edit
^ "Ookinete (Medical Dictionary)". Dictionary.com. Retrieved 2009-12-11.

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Japanese Journal

エゾヒグマ (Ursus arctos yesoensis) における Hepatozoon sp. 寄生について

久保正仁,千葉依里,飯渕るり子,坪田敏男,佐々木基樹,酒井洋樹,柳井徳磨
Japanese journal of zoo and wildlife medicine = 日本野生動物医学会誌 15(2), 111-113, 2010-09-01
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Rhoptry neck protein RON2 forms a complex with microneme protein AMA1 in Plasmodium falciparum merozoites.

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SURFIN4.1, a schizont-merozoite associated protein in the SURFIN family of Plasmodium falciparum.

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NAID 120001253654