Main » Infectious diseases » Soil-mediated Helminthiases » Ascariasis
Photo 1. Ascaris lumbricoide larvae migrating in lung. Eggs passed in the faeces mature in the soil and are ingested together with contaminated food. Indiscriminate defaecation and the consequent distribution of eggs on the soil ensure the continuity of transmission of ascariasis. The prevalence of this worm in the community is a good indication of the standard of personal hygiene and sanitation. The eggs can survive even in a cold climate, and the infection is therefore global in distribution.
The eggs hatch in the human duodenum. The rhabditiform larvae penetrate the mucosa to enter the blood stream, and hence reach the lungs. Here they grow through two larval moults then, like hookworms, they break through into the bronchioles, make their way to the pharynx and are swallowed. The figure shows a section of larva in a bronchiole. This stage is associated with eosinophilia, and pneumonitis may accompany heavy infestations.
Photo 2. Head of adult. This scanning electron micrograph shows the typical head structures. (X 110)
Photo 3. Adult Ascaris. They mature into adult roundworms in the small intestine. The adult males are about 15 to 30 cm long, and females 20 to 35 cm.
Photo 4. A. lumbricoides seen in X-ray. The adults may be seen as filling defects in patients having barium meals for investigation of intestinal symptoms.
Photo 5. Obstruction due to roundworms. Heavy infections, especially in children, may lead to intestinal obstruction. Volvulus is an additional complication in this intestine from a two-year-old child.
Photo 6. Adult roundworms migrating in liver. The adult worms have a marked tendency to penetrate any available hole in their vicinity and may escape through abdominal fistulae following operations such as appendicectomy. They may also block such organs as the common bile duct, and the appendix itself.
Photo 7. Massive Ascaris infection in child. A large bolus of roundworms expelled following anthelminthic treatment.
Photo 8. Ascaris lumbricoides life cycle.
Ascaris lumbricoides adult worms live in the small intestine (A) where they lay large numbers of eggs (B) that are passed out with the faeces. In the soil they can readily contaminate vegetables, for example when nightsoil (C) is used as fertiliser. The larvae develop inside the eggs (D) which are swallowed when they are present in uncooked food (D). The eggs enter the jejunum where the larvae hatch, penetrate the mucosa, and are carried through the hepatic circulation to the heart and lungs (G). There they grow, moulting twice before escaping from the capillaries into the alveoli. They again enter the stomach (H) via the trachea and oesophagus, and thence pass to the small intestine where they grow to adulthood.
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