A roundworm infection begins when you swallow roundworm eggs.
Eggs can be present in food or drink, or in the soil in which food has grown.
Eating food 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 them.
Contaminated soil or stools can also contaminate the water, making it possible to develop a roundworm infection by drinking contaminated water.
When roundworm eggs are swallowed, they 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're swallowed. As the larvae are very small, you'll be unaware of this process.
After they're swallowed, the larvae will end up in the main part of your small intestine, where they'll mature into adult worms. Adult worms 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 60 to 70 days from the initial ingestion of eggs to the production of new ones.
Roundworm infections are most common in parts of the world where: