Ascaris is a genus of parasitic nematode worms known as the "small intestinal roundworms". One species, A. lumbricoides, affects humans and causes the disease ascariasis. Another species, A. suum, typically infects pigs. 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, affecting cognitive processes, inducing tissue reactions such as granuloma to larval stages, and by causing intestinal obstruction, which can be fatal.
- Adult: cylindrical shape, creamy white or pinkish in color
- Male: average 15–30 cm and is more slender than female
- Female: average 20–35 cm in length
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. 
- "Parasites-Ascariasis". Centers for Disease Control and Prevention. Retrieved 30 May 2013.
- 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
- (Sanglas et al., 2008)
- 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.