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Ascaris

From Wikipedia, the free encyclopedia
This article is about the worm. For the infection caused by this worm, see Ascariasis. For the singular of Ascaris, see Ascari (disambiguation).

Ascaris
Adult female
Life cycle inside and outside of the human body of one fairly well described helminth: Ascaris lumbricoides
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Ascaridida
Family: Ascarididae
Genus: Ascaris
Linnaeus, 1758
Species

Ascaris is a nematode genus of parasitic worms known as the "small intestinal roundworms".[1] One species, Ascaris lumbricoides, affects humans and causes the disease ascariasis. Another species, Ascaris suum, typically infects pigs. Other ascarid genera infect other animals, such as Parascaris equorum, the equine roundworm, and Toxocara and Toxascaris, which infect dogs and cats.

Their eggs are deposited in feces and soil. Plants with the eggs on them infect any organism that consumes them.[2] A. lumbricoides is the largest intestinal roundworm and is the most common helminth infection of humans worldwide. Infestation can cause morbidity by compromising nutritional status,[3] affecting cognitive processes,[4] inducing tissue reactions such as granuloma to larval stages, and by causing intestinal obstruction, which can be fatal.

Morphology

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Ascaris cross section
Esophagus of an Ascaris worm
  • Adult: cylindrical shape, creamy white or pinkish in color
  • Male: average 15–30 centimetres (5.9–11.8 in); more slender than the female
  • Female: average 20–35 centimetres (7.9–13.8 in)

The body is long, cylindrical, and fusiform (pointed at both the ends). The body wall is composed of cuticle, epidermis and musculature. There is a pseudocoelom. Respiration is by simple diffusion. The nervous system consists of a nerve ring and many longitudinal nerve cords. Reproduction is exclusively sexual, and males are usually shorter than females.

Defense mechanism

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As part of the parasite defense strategy, Ascaris roundworms secrete a series of inhibitors to target digestive and immune-related host proteases, which include pepsin, trypsin, chymotrypsin/elastase, cathepsins, and metallocarboxypeptidases (MCPs). Ascaris species inhibit MCPs by releasing an enzyme known as Ascaris carboxypeptidase inhibitor (ACI). This enzyme binds to the active site of MCP and blocks the cleavage of its own proteins by the host MCP.[5] Similarly, they inhibit trypsin by releasing the protein Ascaris Trypsin Inhibitor (pdb 1ATA).[6]

History

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Ascaris has been present in humans for at least several thousand years, as evidenced by Ascaris eggs found in paleofeces and in the intestines of mummified humans.[7]

A. lumbricoides was originally called Lumbricus teres and was first described in detail by Edward Tyson in 1683.[8] The genus Ascaris was originally described as the genus for Ascaris lumbricoides by Carl Linnaeus in 1758.[9] The morphologically similar Ascaris suum was described from pigs by Johann August Ephraim Goeze in 1782.[9]

See also

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References

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  1. ^ Carter, Burton J. Bogitsh, Clint E. (2013). Human parasitology, Chapter 16: Intestinal nematodes (4th ed.). Amsterdam: Academic Press. p. 291. ISBN 978-0-12-415915-0. Retrieved 19 November 2015.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ "Parasites-Ascariasis". Centers for Disease Control and Prevention. Retrieved 30 May 2013.
  3. ^ Hall, Andrew; Hewitt, Gillian; Tuffrey, Veronica; de Silva, Nilanthi (April 2008). "A review and meta-analysis of the impact of intestinal worms on child growth and nutrition". Maternal & Child Nutrition. 4 (Suppl. 1): 118–236. doi:10.1111/j.1740-8709.2007.00127.x. PMC 6860651. PMID 18289159.
  4. ^ Jardim-Botelho, A; Raff, S; Rodrigues Rde, A; Hoffman, HJ; Diemert, DJ; Corrêa-Oliveira, R; Bethony, JM; Gazzinelli, MF (2008). "Hookworm, Ascaris lumbricoides infection and polyparasitism associated with poor cognitive performance in Brazilian schoolchildren". Tropical Medicine and International Health. 13 (8): 994–1004. doi:10.1111/j.1365-3156.2008.02103.x. PMID 18627581. S2CID 27755528.
  5. ^ Sanglas, Laura; Aviles, Francesc X.; Huber, Robert; Gomis-Rüth, F. Xavier; Arolas, Joan L. (2009). "Mammalian metallopeptidase inhibition at the defense barrier of Ascaris parasite". Proceedings of the National Academy of Sciences. 106 (6): 1743–1747. Bibcode:2009PNAS..106.1743S. doi:10.1073/pnas.0812623106. PMC 2644108. PMID 19179285.
  6. ^ Grasberger, Bruce L; Clore, G.Marius; Gronenborn, Angela M (1994). "High-resolution structure of Ascaris trypsin inhibitor in solution: direct evidence for a pH-induced conformational transition in the reactive site". Structure. 2 (7): 669–678. doi:10.1016/s0969-2126(00)00067-8. PMID 7922043.
  7. ^ Leles D, Gardner SL, Reinhard K, Iniguez A, Araujo A (2012). "Are Ascaris lumbricoides and Ascaris suum a single species?". Parasites & Vectors. 5 (42): 42. doi:10.1186/1756-3305-5-42. PMC 3293767. PMID 22348306.
  8. ^ Despommier DD, Griffin DO, Gwadz RW, Hotez PJ, Knirsch CA (2017). Parasitic Diseases (6 ed.). Parasites Without Borders. ISBN 978-0-9978400-1-8.
  9. ^ a b Leles D, Gardner SL, Reinhard K, Iniguez A, Araujo A (2012). "Are Ascaris lumbricoides and Ascaris suum a single species?". Parasites & Vectors. 5 (42): 42. doi:10.1186/1756-3305-5-42. PMC 3293767. PMID 22348306.
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