Trophozoite

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

 

Malaria Lifecycle

Plasmodium falciparium

The causative organism of malaria is a protozoan, Plasmodium falciparium, that is carried by the female Anopheles mosquit.^[4] Malaria is recorded as the most common disease in Sub-Saharan Africa and some Asian countries with the highest number of death.^[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]

 

Life cycle of Balantidium coli

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 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]

References

1. Yaeger RG (1996). Baron S (ed.). Protozoa: Structure, Classification, Growth, and Development. University of Texas Medical Branch at Galveston. ISBN 9780963117212.
2. Aguirre García M, Gutiérrez-Kobeh L, López Vancell R (February 2015). "Entamoeba histolytica: adhesins and lectins in the trophozoite surface". Molecules. 20 (2): 2802–2815. doi:10.3390/molecules20022802. PMC 6272351. PMID 25671365.
3. 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. doi:10.1016/j.meegid.2009.05.018. PMID 19539057.
4. White NJ, Pukrittayakamee S, Hien TT, Faiz MA, Mokuolu OA, Dondorp AM (February 2014). "Malaria". Lancet. 383 (9918): 723–735. doi:10.1016/s0140-6736(13)60024-0. PMID 23953767.
5. "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. ISBN 978-1-137-59209-5.
6. Dhiman S (February 2019). "Are malaria elimination efforts on right track? An analysis of gains achieved and challenges ahead". Infectious Diseases of Poverty. 8 (1): 14. doi:10.1186/s40249-019-0524-x. PMC 6375178. PMID 30760324.
7. Walker NF, Nadjm B, Whitty CJ (February 2014). "Malaria". Medicine. 42 (2): 100–106. doi:10.1016/j.mpmed.2013.11.011.
8. 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. PMID 18006365.
9. Mitchell CM, McLemore L, Westerberg K, Astronomo R, Smythe K, Gardella C, et al. (August 2014). "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. doi:10.1093/infdis/jiu176. PMC 4172039. PMID 24652495.
10. 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. PMID 9521324. S2CID 2584314.
11. Wipasa J, Elliott S, Xu H, Good MF (October 2002). "Immunity to asexual blood stage malaria and vaccine approaches". Immunology and Cell Biology. 80 (5): 401–414. doi:10.1046/j.1440-1711.2002.01107.x. PMID 12225376. S2CID 24675596.
12. 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 31 January 2024). ISSN 0019-5138. S2CID 134359453.{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link)
13. 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. PMID 25324127. S2CID 23050925.
14. "Malaria: Control, Elimination, and Eradication". Human Parasitic Diseases. 8: 11–15. 2016. doi:10.4137/hpd.s16590. ISSN 1179-5700.
15. 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. PMID 27501461.