Ascaris lumbricoides, also known as the giant intestinal roundworm, is a parasitic nematode (roundworm) that causes human ascariasis, which is an infection caused by this roundworm in humans. The adult worm can grow up to 40 cm (16 in) in length and 2 cm (0.8 in) in width, making it one of the largest parasites that infect humans.
Humans contract ascariasis by ingesting food or soil contaminated by its eggs. When eggs reach into the intestines, they hatch into larvae. Next, larva migrate to the lungs through blood circulation, where they mature into adult worms, get expectorated and swallowed, eventually returning into the intestines. In the intestines, adult worms mate and produce more eggs, and the cycle starts again. Symptoms depend on whether the worm is in its intestinal or pulmonary phase. They may include dry cough, difficulty in breathing, abdominal pain, diarrhea, and vomiting. Ascaris lumbricoides is diagnosed through a stool sample analysis.