Question

How does the transmission of the following diseases take place?

Ascariasis

Answer 1

Life cycle of Ascaris lumbricoides

The life cycle of Ascaris involves only one host, i.e. humans.

1. Ascaris is present in the gastrointestinal tract and faecal matter. Adult worms live in the lumen of the small intestine.
2. Ingestion of infective eggs takes place from contaminated vegetables and water is the primary route of infection.
3. A female worm may produce approximately 2, 00,000 eggs per day, which are passed with the feces.
4. Unfertilized eggs may be ingested but are not infective.
5. Fertile eggs develop into embryos and become infective after 18 days to several weeks depending on the environmental conditions (Optimum conditions: moist, warm, shaded soil).
6. After swallowing the infective eggs, the larvae hatch and are carried via. circulation to lymphatics and the lungs.
7. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the respiratory tract to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms.
8. Two-three months are required from the ingestion of the infective eggs to oviposition by the adult female. Adult worms can live for 1 to 2 years.
9. The eggs appear in stools after 60-70 days. In larval ascariasis, symptoms occur 4-16 days after infection.

Mode of transmission

1. Food and drinks contaminated with the eggs of these worms is the main mode of transmission.
2. Eggs hatch inside the intestine of the new host.
3. The larvae pass through various organs and settle as adults in the digestive system.