Intestinal roundworms, general characteristics:
Intestinal roundworm parasites are also known as intestinal nematodes, soil-transmitted helminths, soil-transmitted nematodes, and geohelminths. For the effects of these parasites on children (e.g., growth and mentalstunting, which occur even when symptoms such as abdominal pain are lacking), click here. For the number of people infected by these parasites, click here
Giant roundworms (Ascaris lumbricoides). So named because they are the largest intestinal roundworm parasite of humans, reaching up to 40 cm (15 inches!) in length. Parasite eggs mature in the soil and remain infective for years. Upon ingestion, the parasite eggs hatch in the small intestine into small larvae and invade into the bloodstream, where they eventually enter the lungs and then the airspace in the lungs. They return through swallowing into the small intestine, where each giant roundworm can live for 1-2 years. An adult female parasite can produce tremendous amounts of parasitic eggs, up to 240,000/day, which then re-enter the soil via stool, completing the life cycle. The time from initial infection to egg production is 2-3 months. Apart from effects on children’s development and health, other symptoms include coughing and burning sensation during lung phase, mild diarrhea, abdominal pain, and, occasionally, blockage of the intestine or of the biliary tract. These complications can sometimes be quite serious, requiring surgery. The picture shown here is of a similar Ascaris species that lives in pigs and that is use for research, Ascaris suum.
Hookworms (Necator americanus, Ancylostoma duodenale, and less common species such as Ancylostoma ceylanicum). These parasites live in the small intestine, wherein they bury their heads through the intestine into the bloodstream and ingest blood. The amount of blood they ingest can lead to anemia and hence are considered the worst of the intestinal roundworms. Adult hookworms are 1 cm (~0.5 inch) long. The larvae (baby worms) live in the soil waiting to come in contact with human skin. They penetrate the skin, migrate through the blood system and enter the lungs. From there, the larvae penetrate into the airway and induce a coughing reflex, which results in their being swallowed into the small intestine. In the small intestine the hookworms mature in adults. A female hookworm can produce tens of thousands of eggs per day, which exit the body via the stool. Once in the soil, the eggs hatch and develop into infectious larvae. Ancylostoma hookworms can alter enter the intestine via direct ingestion of larvae. Overt symptoms include itching at the site of penetration, abdominal pain, diarrhea, weakness, and shortness of breath. Adult hookworms can live in the human intestine from 1 to 10 years. The time from skin penetration to production of eggs is ~6-8 weeks or longer. Putting shoes on children does not seem to protect them from hookworm infections, perhaps because more than a child’s feet can come in contact with contaminated soil (reference 1). The picture shown here is of the hookworm species Ancylostoma ceylanicum, which can infect humans and is one of the main parasites we work with at Wormfree World Institute.
Whipworms (Trichuris trichiura). Adult parasites reside in the large intestine (colon, cecum) with their anterior heads buried into the intestinal lining, each adult releasing thousands of eggs per day. Infection begins by ingestion of whipworm eggs, which hatch as larvae in the small intestine that then mature and migrate into the large intestine. The complete life cycle (ingestion of eggs to maturation into adults that produce eggs in the colon and release them in stool) is ~3 months. Adult whipworms are 3-5 cm long (~1-2 inches) and can live for years in the human body. Overt symptoms can include abdominal pain, anorexia, and bloody diarrhea. A severe complication associated with heavy whipworm infections is rectal prolapse, in which the walls of the rectum protrude out the anus. Whipworm infections are particularly difficult to treat. The picture shown here is Trichuris muris, mouse whipworm, a close relative of human whipworm and a parasite researched at Wormfree World Institute.
Threadworms (Stongyloides stercoralis). A different and important intestinal roundworm parasite that is able to autoinfect and is potentially deadly to humans. This parasite is not currently the target of Mass Drug Administration.
Hotez, Ann. N.Y. Acad. Sci., 2008, 1136:38-44.Humphries et al., Am. J. Trop. Med. Hyg., 2011, 84:792-800.