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''Ascaris'' is a genus of parasitic nematode worms known as the "small intestinal roundworms", which is a type of parasitic worm. 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". Their eggs are deposited in feces and soil. Plants with the eggs on them infect any organism that consumes them. ''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,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 affecting cognitive processes, 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, 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

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. Similarly, they inhibit trypsin by releasing the protein Ascaris Trypsin Inhibitor (pdb 1ATA,https://www.rcsb.org/structure/1ATA 1ATB)High-resolution structure of Ascaris trypsin inhibitor in solution: direct evidence for a pH-induced conformational transition in the reactive site, Grasberger BL 1 , Clore GM , Gronenborn AM Structure 1 Jul 1994, 2(7):669-678/ref>

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.

History

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

Gallery

Image:Ascarisesophagus.jpg|Esophagus of an ''Ascaris'' worm Image:Ascariscs40x1.jpg|''Ascaris'' cross section 40× Image:Ascariscs40x3.jpg|''Ascaris'' cross section 40× Image:Ascariscs400x1.jpg|''Ascaris'' cross section 400×


See also


* List of parasites (human)


References


{{Taxonbar|from=Q310838 Category:Ascaridida Category:Parasites of equines