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Roundworm Content Supplied by NHS Choices
Symptoms of a roundworm infection

In most cases, a roundworm infection doesn't cause any noticeable symptoms.

When symptoms occur, they usually follow a two-stage course, as described below:

  • Early-phase symptoms - these are caused by the larvae (newly-hatched worms) moving from the small intestine to the lungs. It's unclear why some people develop these symptoms while others don't. 
  • Late-phase symptoms - these are caused by adult worms living in the intestine. The worms can't reproduce inside you. There will only be as many worms as the eggs you first ingested (see causes of roundworm infection for more details about the life cycle of the roundworm).

Early-phase symptoms

The early-phase symptoms of a roundworm infection only affect a small proportion of people and are rare in the UK.

Symptoms usually begin 4-16 days after swallowing the eggs and last up to three weeks. They include:

Late-phase symptoms

The late-phase symptoms of a roundworm infection are even rarer in the UK, particularly in adults. If there are a lot of mature worms in the intestine, they can cause blockages. This won't occur before six weeks after the eggs have been swallowed.

Signs and symptoms associated with mature worms include:

  • passing a worm in your faeces
  • mild stomach (abdominal) pain
  • nausea and vomiting
  • diarrhoea (you may also notice blood in your stools)

However, most people have no symptoms.

If your intestines are blocked due to a large number of worms, you will probably experience vomiting and severe abdominal pain.

Causes of a roundworm infection

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. 

How a roundworm infection progresses

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.

Environmental risk factors

Roundworm infections are most common in parts of the world where:

  • access to sanitation is either limited or non-existent
  • there's overcrowding
  • there are high levels of poverty
  • there's a high population of children under five years of age
  • human faeces are commonly used as fertiliser (known as "night soil")
Treating a roundworm infection

Roundworm infections can be successfully treated using one of a number of medicines.

The three main medicines are:

  • mebendazole
  • piperazine
  • albendazole

These are described below.


Mebendazole is recommended for treating roundworm infections in adults and children over the age of one.

It works by stopping the roundworms using glucose (sugar). Without glucose, the cells of the roundworms lose their energy supply and quickly die.

A three-day course of mebendazole is usually recommended. This involves taking one tablet twice a day.

Stomach pain is the most common side effect of mebendazole. Less common side effects include:


Piperazine is recommended for babies aged 3-11 months. It's available as a powder that you dissolve in water. Most children only require a single dose.

Side effects of piperazine can include:

  • stomach (abdominal) pain
  • nausea and vomiting 
  • colic (excessive, frequent crying) 
  • diarrhoea

These side effects should pass quickly once the medicine works its way out of the body.

If your child is less than three months of age, delaying treatment until they reach three months may be recommended.


Albendazole is commonly used in tropical countries, but is currently unlicensed for use in the UK.

This means the medicine's manufacturer hasn't applied for a license for albendazole to be used to treat roundworm in the UK. However, it's been extensively studied in countries where roundworm is common, and has been shown to be safe and effective.


While there's no firm evidence to suggest that any of the medications above can cause birth defects, they're not usually recommended during pregnancy.

Roundworms can occasionally cause troublesome symptoms, but they don't usually pose a threat to your unborn child.

Preventing a roundworm infection

As well as treating roundworm infections with medication, the infection can be controlled by improving sanitation and health education.

Although treatments are usually effective, preventing roundworm infections that affect tropical countries is very challenging.

Infection control

Good hand hygiene can help prevent the spread of roundworm. Always wash your hands thoroughly:

  • after using the toilet
  • after changing a nappy
  • after touching soil
  • before preparing and eating food

Travel advice

You'll need to take extra precautions when travelling to parts of the world where roundworm is widespread, sanitation is poor and the climate is hot.

Places where roundworm is particularly widespread include:

  • Asia particularly China, India and the large islands of East Asia, such as Indonesia
  • sub-Saharan Africa (all the countries south of the Sahara Desert) such as Kenya and Nigeria
  • South and Central America, and the Caribbean
  • the Middle East

If you're travelling to these parts of the world, you should:

  • only drink bottled or boiled water
  • avoid eating raw fruit or vegetables
  • wash your hands thoroughly if you come into contact with soil
  • eat hot food that's been cooked thoroughly

Read more about travel health and food and water abroad.