The life cycle of roundworms
A roundworm infection begins when you come into contact with food, water or soil that has been contaminated with ascaris (roundworm) eggs. For example, eating food that has been grown in contaminated soil can expose you to infection. You may also become infected if you touch contaminated soil with your hands and then eat without first washing your hands.
The eggs move into the first section of the small intestine, known as the duodenum.
After one to two weeks, the eggs will hatch into larvae and move through the wall of your intestine into your bloodstream, where they reach your lungs. The larvae will pass from your lungs into your throat, where they are swallowed. As the larvae are very small, you will be unaware of this process.
After they are swallowed, the larvae will end up in the main part of your small intestine, where they will mature into adult worms. These can live for up to two years. Female worms can lay up to 200,000 eggs a day. The eggs are released in your stools (faeces). It takes between 60 and 70 days from the initial ingestion of eggs to the production of new eggs.
Environmental risk factors
Roundworm infections are most common in parts of the world where:
- access to sanitation is either limited or non-existent
- there is overcrowding
- there are high poverty levels
- there is a high population of children under five years of age
- human stools (faeces) are commonly used as fertiliser (known as ‘night soil’)
Roundworm eggs can live in soil for several years, which means that people who come into contact with contaminated soil, or eat food that has been grown in contaminated soil, are at risk of developing a roundworm infection.
Contaminated soil or stools can also contaminate the water, making it possible to develop a roundworm infection by drinking contaminated water.
