Ascariasis - Ascariasis is an infection caused by the roundworm Ascaris lumbricoides. Infection occurs when an individual consumes food or drink contaminated with fecal matter that contains mature worm eggs. Adult worms can reside in the small intestine and produce eggs for a year or more.

Whipworm (trichuriasis) - A whipworm infection occurs when an individual consumes food or drink contaminated with fecal matter containing the roundworm Trichuris trichiura. After eggs are ingested, larvae hatch in the small intestine and mature in the large intestine.

Hookworm (ancylostomiasis) - A hookworm infection occurs when larvae of the roundworms Ancylostoma duodenale or Necator americanus penetrate human skin, making their way through the lungs to the small intestine, where they attach and mature into adults, laying more eggs. Children are particularly susceptible to this kind of infection. Once infected, children become weak and experience delayed growth patterns. These roundworms infect about 25% of the world's population.

Threadworm (strongyloidiasis) - Threadworm is an infection caused by the roundworm Strongyloides stercorali. This type of roundworm infects humans in the same way as Ancylostoma duodenale. About half of the population of some African countries has been infected with Strongyloides stercorali.

Pinworm (enterobiasis) - A pinworm infection occurs when an individual consumes food or drink contaminated with fecal matter containing the roundworm Enterobius vermicularis. After being ingested, eggs hatch in the small intestine and adult worms ultimately inhabit the large intestine. The pregnant female worms migrate to the anus and deposit large numbers of eggs in the skin around that area. Pinworm, which is commonly spread in day care centers, schools, and camps, affects as many as one-third of all American children.

Visceral larva migrans, or VLM (toxocariasis) - VLM is an infection caused by the roundworms Toxocara canis, Toxocara cati, or Baylisascaris procyonis. These parasites ordinarily infect dogs, cats, and raccoons, respectively, but a human can become infected by consuming soil contaminated by infected animal feces. While the larvae do not mature to adults in humans, they penetrate the intestinal wall and migrate to various parts of the body, particularly the lungs and liver.

Trichinosis (trichiniasis) - Trichinosis an infection caused by the roundworm Trichinella spiralis. These larvae live in pigs and other wild carnivores, such as bears, but humans can become infected with Trichinella spiralis when they eat such meat (particularly pork) that is undercooked. The larvae mature in small intestines and migrate to muscle cells where they can live for months or years.

Guinea worm disease (dracunculosis) - Humans can become infected with Guinea worm disease when they consume drinking water contaminated with the roundworm Dracunculus medinensis. Larvae penetrate the intestinal wall, where they mature and migrate to connective tissues. This type of roundworm infects 10 to 40 million people annually worldwide, primarily in the Indian subcontinent, West and Central Africa, and some Middle Eastern countries.

Lymphatic filariasis - A lymphatic filariasis infection occurs when an individual is bitten by a mosquito containing the roundworms Wucheria bancrofti, Brugia malayi, or Brugia timori. Over a period of 6 to 12 months, adult worms mature and live in human lymph vessels and nodes and can eventually circulate through the blood. About 90 million people worldwide have been infected with these roundworms.

River blindness (onchocerciasis) - River blindness is an infection caused by the roundworm Onchocerca volvulus. Onchocerciasis, which is spread by day-biting flies, is the leading cause of blindness worldwide, affecting about 20 million people, mostly in Africa.

Loiasis - Loiasis is an infection caused by the roundworm Loa loa. Like river blindness, loiasis is spread by day-biting flies. An estimated 3 to 13 million people in equatorial Africa have been infected with Loa loa.