If human faeces are not disposed of in a hygienic way, or if sewerage sludge is used as a garden fertiliser, children can swallow and get infected by roundworm eggs. Roundworm eggs can survive in soil for years. Playing or crawling in contaminated soil or eating raw vegetables that have not been washed may result in infection. High prevalence rates are common in communities with poor sanitation. This is a major public health problem in many parts of South Africa.

Roundworm eggs hatch in the child’s small bowel, and the newly hatched larvae then pass through the bowel wall into the bloodstream and are carried to the alveoli of the lungs. From here they make their way up the bronchi and trachea then get swallowed. In the small bowel the roundworm larvae mature into adult worms where they can live for 2 years.