Activated, feeding stage in the life cycle of certain protozoa
Atrophozoite (G.trope, nourishment +zoon, animal) is the activated, feeding stage in the life cycle of certainprotozoa such asmalaria-causingPlasmodium falciparum and those of theGiardia group.[1] The complementary form of the trophozoite state is the thick-walledcyst 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.[2] 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.[3]
The causative organism ofmalaria is a protozoan,Plasmodium falciparium, that is carried by the femaleAnopheles mosquito.[4] Malaria is recorded as the most common disease in Sub-Saharan Africa, and some Asian countries with the highest number of deaths.[5] Studies have shown the increased prevalence of this disease since 2015.[6] This protozoan has several other subspecies, with some causing diseases in humans with over 91,000 death in 2021 from malaria (Plasmodium falciparium) alone, which is a 77% increase from 2020 as reported by the World Health Organization (WHO).[7]
Human: The infected female mosquito (usually Anopheles species) bites a human and injectssporozoites into the bloodstream during a bloodmeal.[8] The sporozoites travel to the liver where they invade liver cells (hepatocytes) in the Exo-erythrocytic Cycle.[9] The sporozoites in the infected liver cells ruptures intoschizonts which enter into the blood of the individual (Erythrocytic Cycle). The schizonts mature and divide asexually to form thousands ofmerozoites[10] in the early trophozoite phase, which cause the malaria symptoms in humans. These mature and go through sexual reproduction, known as gametogenesis to produce thegametocytes (occurring in male and female forms)[11] in the late trophozoite phase in the bloodstream that are picked up by other mosquitoes during blood meals.[12][13]
Mosquito: The gametocytes, flagellated microgametocytes (males) and the unflagellated megagametocytes (females) are ingested during bloodmeal by mosquitoes, which then enter into the cyst phase, sporozoites, and undergo a series of asexual reproduction. After a span of 10-18 days, the sporozoite moves to the mosquito's salivary gland. In a subsequent blood meal on another human, anticoagulant saliva is injected along with the sporozoites, which then migrate to the liver, initiating a new cycle.[14]
The trophozoite life stage ofGiardia colonizes and proliferates in the small intestine. Trophozoites develop during the course of the infection into cysts which is the infectious life stage.[15]
^López-Soto F, León-Sicairos N, Reyes-López M, Serrano-Luna J, Ordaz-Pichardo C, Piña-Vázquez C, et al. (December 2009). "Use and endocytosis of iron-containing proteins by Entamoeba histolytica trophozoites".Infection, Genetics and Evolution.9 (6):1038–1050.Bibcode:2009InfGE...9.1038L.doi:10.1016/j.meegid.2009.05.018.PMID19539057.
^"Pan American Health Organization (PAHO) Regional Office of the World Health Organization (WHO)".The Grants Register 2018. London: Palgrave Macmillan UK. 2018. p. 584.doi:10.1007/978-1-349-94186-5_904.ISBN978-1-137-59209-5.
^Kooij TW, Matuschewski K (December 2007). "Triggers and tricks of Plasmodium sexual development".Current Opinion in Microbiology.10 (6):547–553.doi:10.1016/j.mib.2007.09.015.PMID18006365.
^Billker O, Lindo V, Panico M, Etienne AE, Paxton T, Dell A, et al. (March 1998). "Identification of xanthurenic acid as the putative inducer of malaria development in the mosquito".Nature.392 (6673):289–292.Bibcode:1998Natur.392..289B.doi:10.1038/32667.PMID9521324.S2CID2584314.
^Rajagopalan PK (2019-04-02). "Malaria Remains Unshaken and the Mighty Mosquito Remains Unbeaten".Journal of Communicable Diseases.51 (1):43–49.doi:10.24321/0019.5138.201906 (inactive 1 November 2024).ISSN0019-5138.S2CID134359453.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
^Gazzinelli RT, Kalantari P, Fitzgerald KA, Golenbock DT (November 2014). "Innate sensing of malaria parasites".Nature Reviews. Immunology.14 (11):744–757.doi:10.1038/nri3742.PMID25324127.S2CID23050925.
^Einarsson E, Ma'ayeh S, Svärd SG (December 2016). "An up-date on Giardia and giardiasis".Current Opinion in Microbiology.34:47–52.doi:10.1016/j.mib.2016.07.019.PMID27501461.
