Ascaris

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

Ascaris is a genus of parasitic nematode worms known as the "small intestinal roundworms", which is a type of helminth (parasitic worm).[1] One species, Ascaris lumbricoides, affects humans and causes the disease ascariasis. Another species, Ascaris suum, typically infects pigs. Parascaris equorum, the equine roundworm, is also commonly called an "Ascarid".[2]

Their eggs are deposited in feces and soil. Plants with the eggs on them infect any organism that consumes them.[3] 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,[4] affecting cognitive processes,[5] inducing tissue reactions such as granuloma to larval stages, and by causing intestinal obstruction, which can be fatal.

Morphology

  • Adult: cylindrical shape, creamy white or pinkish in color
  • Male: average 15–30 cm (6-12 inches) and is more slender than female
  • Female: average 20–35 cm (8-14 inches) in length

The body is long, cylindrical, fusiform (pointed at both the ends), body wall is composed of cuticle, epidermis and musculature. Presence of a false body pseudocoelom not lined by epithelium. Digestive system is complete. Respiration by simple diffusion. Nervous system consists of a nerve ring and many longitudinal nerve cords. Only sexual reproduction. Sexes are separate with sexual dimorphism. Males are usually shorter than females.

Defense mechanism

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.[6]

Evolution

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]

History

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.[7] The morphologically similar Ascaris suum was described from pigs by Johann August Ephraim Goeze in 1782.[7]

See also

References

  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.
  2. ↑ "Parasites:Ascarids". eXtension. September 27, 2011. Retrieved 9 November 2014.
  3. ↑ "Parasites-Ascariasis". Centers for Disease Control and Prevention. Retrieved 30 May 2013.
  4. ↑ Hall, A., G. Hewitt, V. Tuffrey and N. de Silva (2008). A review and meta-analysis of the impact of intestinal worms on child growth and nutrition. Maternal and Child Nutrition, 4 (Suppl 1): 118-236
  5. ↑ Jardim-Botelho, A; Raff, S; Rodrigues Rde, A; Hoffman, HJ; Diemert, DJ; Corrêa-Oliveira, R; Bethony, JM; Gazzinelli, MF. "Hookworm, Ascaris lumbricoides infection and polyparasitism associated with poor cognitive performance in Brazilian schoolchildren". tropical medicine and international health. 13: 994–1004. doi:10.1111/j.1365-3156.2008.02103.x. PMID 18627581.
  6. ↑ Sanglas, Laura; Aviles, Francesc X.; Huber, Robert; Gomis-Ruth, F. Xavior; Arolas, Joan L. 2008. Mammalian metallopeptidase inhibition at the defense barrier of Ascaris parasite. University of Barcelona, Spain.
  7. 1 2 3 Leles D, Gardner SL, Reinhard K, Iniguez A, Araujo A (2012). "Are Ascaris lumbricoides and Ascaris suum a single species?". Parasites & Vectors. 5 (42). doi:10.1186/1756-3305-5-42.
  8. ↑ Despommier DD, Griffin DO, Gwadz RW, Hotez PJ, Knirsch CA (2017). Parasitic Diseases (6 ed.). ISBN 978-0-9978400-1-8.
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