Estimates suggest that one quarter of the world's population is infected with the intestinal roundworm Ascaris lumbricoides. The vast majority of infected people are asymptomatic. Patients who are newly infected may have pulmonary symptoms (e.g. cough, wheezing) and eosinophilia due to larval migration through the lungs. Later, abdominal symptoms may develop because of the mechanical effects of the relatively large adult worm. Patients in this later stage do not demonstrate eosinophilia. The adult A lumbricoides is a large, cream-colored worm. Adult males are 6-12 inches (15-30cm) in length, and adult females are 8-14 inches (20-35cm) in length. Adult worms can live in the small intestine for 6 months or longer.
The roundworm life cycle begins when eggs from adult female worms living in the intestine are passed out with feces. These eggs then contaminate the soil and, and in warm moist conditions, will develop to the stage where they can become infective. These eggs are then swallowed, for example on fruits or vegetables that have been watered with water containing contaminated soil. Once they are in the intestine (specifically, the duodenum), the eggs hatch into larvae which penetrate the wall of the intestine and enter blood or lymph vessels and end up in the lungs. There they continue to grow and develop, before moving to the throat, to be swallowed back down to the intestine. Here the worms grow and develop to maturity and start producing eggs.
Children, because of their habits (e.g. directly or indirectly consuming soil), are more commonly and more heavily infected than adults. Males are more likely to be infected because boys, it is believed, eat more dirt than girls do.
Early (4-16 days after egg ingestion) symptoms of the tissue-migratory phase include fever, cough, wheezing. Late (6-8 weeks after ingestion) GI symptoms resulting from mechanical irritation include vague abdominal complaints (i.e. cramping, nausea, vomiting); small bowel obstruction (mostly in children); pancreatitis (secondary to worm migration); cholecystitis (secondary to worm migration); appendicitis (less common, secondary to worm migration).
Physical signs include passage of adult worm(s) from mouth or anus; wheezing (early infection); mild abdominal tenderness (established infection).
Types of roundworm called Strongyoides and Ascaris lumbricoides can cause increased intestinal permeability.