Ascariasis is a disease caused by the infestation of parasitic nematodes, particularly of the genus Ascaris. Ascaris is a genus of parasitic nematodes. They belong to the family Ascarididae, Phylum Nematoda. It includes species of nematodes that infect the intestines of humans, [pig]]s, and horses. For instance, Ascaris lumbricoides is a parasitic gut dwelling nematode worm. It is regarded as the largest intestinal roundworm and infests human intestines. Another is the ascarid of pigs, particularly Ascaris suum. A. suum is a species of parasitic nematode usually found in domestic pigs and a few other animals. Human infestation can also occur, presumably as result of handling pig manure, and can lead to intestinal obstruction. Ascaris equorum is a large heavy-bodied ascarid nematode extremely common in the small intestine of horses and other equids. Larvae may develop in man or mice, but do not reach the adult stage.
Infestation with Ascaris lumbricoide may not lead to manifestation of symptoms. The lack of symptoms is associated with the small number of worms. But when the number of worms is high the symptoms may manifest such as malnutrition, allergies, intestinal blockage, shortness of breath, fever, diarrhea, and abdominal pain and swelling. Ascaricides are used for treating ascariasis.