The Organism
Adult Ascaris are large: Females are 20–50 centimeters long, and males are 15–30 centimeters long (Figure 1A).
Fig1. A. lumbricoides. A: Adult females are larger than the adult male worms (length of ruler = 16 centimeters). B: An Ascaris egg (55–75 μm) with characteristic bumps (mammilated). (Used with permission from Sullivan J: A Color Atlas of Parasitology, 8th ed. 2009.)
Humans acquire the infection after eggs are ingested; larvae hatch in the duodenum, penetrate through the mucosa, migrate in the circulatory system, lodge in lung capillaries, penetrate the alveoli, and migrate from the bronchioles to the trachea and pharynx; larvae are swallowed and return to the intestine and mature into adults. After mating, females can release 200,000 eggs per day, which are passed in the feces. Eggs are infective after about 1 month in the soil and are infectious for several months (Figure 1B).
Pathology and Pathogenesis
If present in high numbers, adult worms may cause mechanical obstruction of the bowel and bile and pancreatic ducts. Worms tend to migrate if drugs such as anesthetics or steroids are given, leading to bowel perforation and peritonitis, anal passage of worms, vomiting, and abdominal pain. Larvae migrating through lungs induce an inflammatory response (pneumonitis), especially after second infection, leading to bronchial spasm, mucus production, and Löeffler’s syndrome (cough, eosinophilia, and pulmonary infiltrates).
