ESSENTIALS OF DIAGNOSIS
Transient cough, urticaria, pulmonary infiltrates, eosinophilia.
Nonspecific abdominal symptoms.
Eggs in stool; adult worms occasionally passed.
Ascaris lumbricoides is the most common of the intestinal helminths, causing about 800 million infections, 12 million acute cases, and 10,000 or more deaths annually. Prevalence is high wherever there is poor hygiene and sanitation or where human feces are used as fertilizer. Heavy infections are most common in children.
Infection follows ingestion of eggs in contaminated food. Larvae hatch in the small intestine, penetrate into the bloodstream, migrate to the lungs, and then travel via airways back to the GI tract, where they develop to adult worms, which can be up to 40 cm in length, and live for 1–2 years (eFigure 35–34).
Life cycle of Ascaris lumbricoides (the giant roundworm of humans). Adult worms
, live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces
. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks
, depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed
, the larvae hatch
, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs
. The larvae mature further in the lungs (10–14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed
. Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1–2 years. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)
Most persons with Ascaris infection are asymptomatic. In a small proportion of patients, symptoms develop during migration of worms through the lungs, with fever, nonproductive cough, chest pain, dyspnea, and eosinophilia, occasionally with eosinophilic pneumonia. Rarely, larvae lodge ectopically in the brain, kidney, eye, spinal cord, and other sites and may cause local symptoms.
Light intestinal infections usually produce no symptoms. With heavy infection, abdominal discomfort may be seen. Adult worms may also migrate and be coughed up, be vomited, or may emerge through the nose or anus. They may also migrate into the common bile duct, pancreatic duct, appendix, and other sites, which may lead to cholangitis, cholecystitis, pyogenic liver abscess, pancreatitis, obstructive jaundice, or appendicitis. With very heavy infestations, masses of worms may cause intestinal obstruction, volvulus, intussusception, or death. Although severe manifestations of infection are uncommon, the very high prevalence of ascariasis leads to large numbers of individuals, especially children, with important sequelae. Moderate to ...