Ascaris

Infection is spread by ingestion of fertile eggs from contaminated hands, food or water. Ascaris lumbricoides and Ascaris suum are the common pathogens. A.suum is transmitted from pigs. After ingestion of fertile eggs, they hatch in the small intestine and invade the mucosa. They travel via the portal and systemic circulation to the lungs. From there, they may ascend the bronchi, reach the throat and are swallowed or they may penetrate the alveoli. The adult worms live in the small intestine.

Infection may be asymptomatic. Heavy infections may present as abdominal pain and discomfort, intestinal obstruction and sometimes perforation, growth retardation and malnutrition in children especially vitamin A deficiency and protein energy malnutrition. Migrating adult worms can occlude the biliary tree, appendicitis or may be extruded out of the nasopharynx. Loeffler’s syndrome is caused by larvae migrating through the lung. It presents as fever, dry cough, dyspnea, eosinophilia and urticaria. Diagnosis is by demonstration of eggs in stool samples.

Unfertilized egg of A. lumbricoides in an unstained wet mount, 200x magnification.

Fertilized egg of A. lumbricoides in an unstained wet mount of stool.