Trophozoite Explained

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.[1] The complementary form 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. [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]

Life cycle stages

Plasmodium falciparium

The causative organism of malaria is a protozoan, Plasmodium falciparium, that is carried by the female Anopheles 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]

The Malaria lifecycle is divided into two phases:

  1. Human: The infected female mosquito (usually Anopheles species) bites a human and injects sporozoites 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 into schizonts which enter into the blood of the individual (Erythrocytic Cycle). The schizonts mature and divide asexually to form thousands of merozoites[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 the gametocytes (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.d[12] [13]
  2. 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]

Balantidium coli

Balantidium coli is the causative agent of balantidiasis. In the apicomplexan life cycle the trophozoite undergoes schizogony (asexual reproduction) and develops into a schizont which contains merozoites.

Giardia

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.[15]

Notes and References

  1. Book: Yaeger RG . . Medical Microbiology --> . University of Texas Medical Branch at Galveston . Baron S . 1996 . 9780963117212 .
  2. Aguirre García M, Gutiérrez-Kobeh L, López Vancell R . Entamoeba histolytica: adhesins and lectins in the trophozoite surface . Molecules . 20 . 2 . 2802–2815 . February 2015 . 25671365 . 6272351 . 10.3390/molecules20022802 . free .
  3. López-Soto F, León-Sicairos N, Reyes-López M, Serrano-Luna J, Ordaz-Pichardo C, Piña-Vázquez C, Ortiz-Estrada G, de la Garza M . 6 . Use and endocytosis of iron-containing proteins by Entamoeba histolytica trophozoites . Infection, Genetics and Evolution . 9 . 6 . 1038–1050 . December 2009 . 19539057 . 10.1016/j.meegid.2009.05.018 . 2009InfGE...9.1038L .
  4. White NJ, Pukrittayakamee S, Hien TT, Faiz MA, Mokuolu OA, Dondorp AM . Malaria . Lancet . 383 . 9918 . 723–735 . February 2014 . 23953767 . 10.1016/s0140-6736(13)60024-0 .
  5. Book: Pan American Health Organization (PAHO) Regional Office of the World Health Organization (WHO) . 2018 . The Grants Register 2018 . 584 . London . Palgrave Macmillan UK. 10.1007/978-1-349-94186-5_904 . 978-1-137-59209-5 .
  6. Dhiman S . Are malaria elimination efforts on right track? An analysis of gains achieved and challenges ahead . Infectious Diseases of Poverty . 8 . 1 . 14 . February 2019 . 30760324 . 10.1186/s40249-019-0524-x . 6375178 . free .
  7. Walker NF, Nadjm B, Whitty CJ . February 2014 . Malaria . Medicine . en . 42 . 2 . 100–106 . 10.1016/j.mpmed.2013.11.011.
  8. Kooij TW, Matuschewski K . Triggers and tricks of Plasmodium sexual development . Current Opinion in Microbiology . 10 . 6 . 547–553 . December 2007 . 18006365 . 10.1016/j.mib.2007.09.015 .
  9. Mitchell CM, McLemore L, Westerberg K, Astronomo R, Smythe K, Gardella C, Mack M, Magaret A, Patton D, Agnew K, McElrath MJ, Hladik F, Eschenbach D . 6 . Long-term effect of depot medroxyprogesterone acetate on vaginal microbiota, epithelial thickness and HIV target cells . The Journal of Infectious Diseases . 210 . 4 . 651–655 . August 2014 . 24652495 . 10.1093/infdis/jiu176 . 4172039 .
  10. Billker O, Lindo V, Panico M, Etienne AE, Paxton T, Dell A, Rogers M, Sinden RE, Morris HR . 6 . Identification of xanthurenic acid as the putative inducer of malaria development in the mosquito . Nature . 392 . 6673 . 289–292 . March 1998 . 9521324 . 10.1038/32667 . 2584314 . 1998Natur.392..289B .
  11. Wipasa J, Elliott S, Xu H, Good MF . Immunity to asexual blood stage malaria and vaccine approaches . Immunology and Cell Biology . 80 . 5 . 401–414 . October 2002 . 12225376 . 10.1046/j.1440-1711.2002.01107.x . 24675596 . free .
  12. Rajagopalan PK . 2019-04-02 . Malaria Remains Unshaken and the Mighty Mosquito Remains Unbeaten . Journal of Communicable Diseases . 51 . 1 . 43–49 . 10.24321/0019.5138.201906 . 31 January 2024 . 134359453 . 0019-5138.
  13. Gazzinelli RT, Kalantari P, Fitzgerald KA, Golenbock DT . Innate sensing of malaria parasites . Nature Reviews. Immunology . 14 . 11 . 744–757 . November 2014 . 25324127 . 10.1038/nri3742 . 23050925 .
  14. 2016 . Malaria: Control, Elimination, and Eradication . Human Parasitic Diseases . 8 . 11–15 . 10.4137/hpd.s16590 . 1179-5700.
  15. Einarsson E, Ma'ayeh S, Svärd SG . An up-date on Giardia and giardiasis . Current Opinion in Microbiology . 34 . 47–52 . December 2016 . 27501461 . 10.1016/j.mib.2016.07.019 .

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