Intestinal Roundworm
Rev 09/06/2025
Ref: Roberts and Janovy, 2009; Wikipedia
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Occurs worlwide with infections most copmmon in tropical and subtropical regions.
Considered the most common parasitic worm in humans. An estimated 807 million-1.2 billion people are infected with Ascaris lumbricoides worldwide.(CDC, Lasket, 2008).
People living in tropical and subtropical countries are at greater risk of infection, largely due to living conditions, lack of access to unconteminated water and poor sanitation.
Infection by Ascaris lumbricoides is known as ascariasis.
Human
Intestinal roundworm
Adult hookworms (Ancylostoma duodenale and Necator americanus) parasitize the upper part of the human small intestine, whereas Ascaris lumbricoides parasitize the entire small intestine and adult Trichuris trichiura live in the large intestine, especially the caecum.
The parasites can live for several years in the human gastrointestinal tract. After mating, each adult female produces thousands of eggs per day which leave the body in the feces.
Ecophysiological Parameters:
Ascaris lumbricoides infects humans via the fecal-oral route.
Eggs released by adult females are shed in feces. Unfertilized eggs, often observed in fecal samples, never become infective. Fertilized eggs embryonate and become infectious after 18 days to several weeks in soil, depending on the environmental conditions
Infection occurs when a human swallows water or food contaminated with embryonated eggs. In the duodenum, a rhabditiform larvae hatch from the ingested eggs.
Larvae penetrate intestinal mucosa and submucosa and enter capillaries or lymphatic channels. They pass through the heart and enter the pulmonary circulation and break through the walls of pulmonary capillaries to enter alveoli of the lungs. From the alveoli, larvae migrate through the bronchioles to the trachea.
Once in the trachea, the worms are coughed up into the pharynx and then swallowed again. They pass through the stomach and into the small intestine where they mature to adults.
After mating, aadult females begin producing fertilized eggs within 60�65 days after being singested. Females produce as many as 200,000 eggs per day for 12�18 months. Fertilized eggs become infectious after two weeks in soil; they can persist in soil for 10 years or more.
Refs: CDC, Murray et al., 2005; Read and Sharping, 1995, Wikipedia
Contact with soil contaminated with eggs or larvae of nematode parasites is a common form of transmission that results in human infection. The nematodes can live for years as adults in the human intestinal tract. Soil becomes contaminated by fecal material of infected humans and other animal hosts.
More than a billion people are infected with at least one species. The most important nematode infections of the human gastrointestinal tract are the intestinal roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworm (Necator americanus or Ancylostoma duodenale).
It is common for a single individual, especially a child living in a less developed country, to be chronically infected with all three of the nematode parasites, which results in malnutrition, stunted growth stunting, retarded intellectual development, and cognitive and educational deficiencies.
Bethony, J., Brooker, S., Albonico, M., Geiger, S.M., Loukas, A., Diemert, D., Hotez, P.J. 2006. Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm. The Lancet 9521:1521-1532.
Centers for Disease Control (CDC) 2018. Parasites - Ascariasis. (14 February 2018). Retrieved from www.cdc.gov/parasites/ascariasis/biology.html
Lasker, A. 2008. eMeedicine: Ascaris lumbricoides
Murray, P.R.; Rosenthal, K.S.; Pfaller, M.A.2005 Medical Microbiology, Fifth Edition. United States: Elsevier Mosby,
Read, A. F.; Sharping, A. 1995. The evolution of tissue migration by parasitic nematode larvae. Parasitology. 111:359-371
Roberts, L.S.; Janovy, J. Jr. 2009. Foundations of Parasitology, Eighth Edition. United States: McGraw-Hill.
Wikipedia, accessed Septmber, 2025
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