Ascaris is a genus of parasitic nematode worms known as the "Small intestinal roundworms". One species, A. suum, typically infects pigs, while another, A. lumbricoides, affects humans, typically people living in sub-tropical and tropical areas with poor sanitation. Their eggs are deposited in feces and soil. Plants with the eggs on them will infect any organism that consumes them.  A. lumbricoides is the largest intestinal roundworm and is the most common helminth infection of humans worldwide, a disease known as ascariasis. 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.
- small intestine
- Bloody sputum
- Low-grade fever
- Vomiting worms
- Passing of worm in stool
- Gallstone formation
- Liver abscesses
- Pulmonary eosinophilia
- Abdominal X-ray
- Complete blood count
- Stool ova and parasite exam
A.lumbricoides is known as Ascaris pneumonitis. In the lung it causes hemorrhage, inflammation, and bacterial infection. It also causes allergy in areas with seasonal transmission. This typically occurs at 6–15 days after initial exposure.
The intestinal phase causes malnourishment, intestinal blockage, verminous intoxication. A.lumbricoides will move around in the body in response to chemotherapy or fever. Typically occurs at 6 to 8 weeks after initial exposure.
Early diagnosis can be performed by examination of stool for the worm eggs. The spread or infection of A.lumbricoides can be controlled by proper disposal of feces and proper washing of food. Control of helminthiasis is based on drug treatment, improved sanitation and health education.
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 inhibits 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 (Sanglas et al., 2008)
Infections with A.lumbricoides are easily treated with a number of single dose anthelmintic drugs, which ensures compliance:
- pyrantel pamoate or embonate given as a single oral dose of 10 mg/kg body weight; 
- levamisole given as a single oral dose of 2.5 mg/kg body weight;
- mebendazole given as a single oral dose of 500 mg for all individuals older than 1 years or 100 mg twice daily for 3 days;
- albendazole given as a single oral dose of 400 mg for all individuals older than 2 year and 200 mg for a child aged 12 - 24 months.
The drugs levamisole and pyrantel and its derivatives act by paralysing worms so that they are expelled from the gut by the normal action of peristalsis. The benzimidazole drugs albendazole and mebendazole interfere with the assembly of microtubules in mitochondria and block the uptake of glucose so that the worms are killed and pass out of the gut in the stools. Neither albendazole nor mebendazole are well absorbed from the gut, but any absorbed drug is rapidly metabolised in the liver and is excreted in the urine. 
The World Health Organization recommends mass treatment of all children once a year in areas where more than 20% of children are infected and mass treatment twice a year where more than 50% of children are infected.  The cost-effectiveness of the lower threshold has been questioned. 
Many parasitic disease specialists are seeing increased incidence and recurrence of roundworm in the U.S. and are thereby increasingly recommending follow up courses of medication to treat internal eggs which have not yet hatched, in addition to the initial treatment period as above. This consists of sporadic treatment with albendazole or similar for a period of three days each month for up to five months after the initial treatment period.
When worms are present in large numbers they may block the intestine or the bile or pancreatic ducts, which may require surgery to remove the worms.
- "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
- World Health Organization (2008) WHO Model Formulary. Geneva: World Health Organization. http://apps.who.int/medicinedocs/documents/s16879e/s16879e.pdf
- World Health Organization (1995) WHO Model Prescribing Information. Drugs used in Parasitic Diseases. Second edition. Geneva: World Health Organization.
- World Health Organization (2006). Preventive chemotherapy in human helminthiasis. Geneva: World Health Organization.
- Hall, A., S. Horton and N. de Silva (2009). The costs and cost-effectiveness of mass treatment for intestinal nematode worm infections using different treatment thresholds. PLoS Neglected Tropical Diseases, 3 (3): e402. http://www.plosntds.org/article/info%3Adoi%2F10.1371%2Fjournal.pntd.0000402
- 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.