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What are roundworms?

Roundworms are worms that can infest the human digestive tract, specifically the small intestine.

A roundworm infection is also sometimes known as ascariasis or acaris.

Roundworms are parasites. This means that they use the human body to stay alive, feed and reproduce.

In most people, a roundworm infection does not cause any noticeable symptoms. People most commonly see their doctor because they have seen a worm in their faeces (stools).

Roundworms are the only worms found in human faeces that are roughly the size of an earth worm.

Less commonly symptoms can include a high temperature and dry cough 4-16 days after swallowing the eggs. If a large number of eggs have been ingested, or if the worms move from the small intestine to other parts of the body, they can cause serious complications such as a bowel obstruction.


symptoms of roundworm
for more information.

How infection occurs

A roundworm infection can occur if someone swallows the microscopic ascaris eggs in contaminated food or water.

It is also possible for someone to transfer eggs from their hands to their mouth if they touch contaminated soil.

After the eggs mature into adult worms, the worms produce more eggs. The eggs are released from the body through the bowel and can then infect other humans.

The more roundworms inside your body, the worse your symptoms are likely to be.


causes of roundworm infection
for more information.

Who is affected?

Roundworm infections are one of the most common health conditions in the world - around a quarter of the world’s population currently has a roundworm infection.

Roundworm infections are most widespread in tropical and sub-tropical areas, particularly in parts of the world that are overcrowded and have poor sanitation.

If you notice a roundworm in your faeces or have unexplained asthma-like symptoms shortly after you have visited a tropical or sub-tropical country, see your doctor.

Roundworm can be diagnosed by examining a stool sample under a microscope, to see if there are any eggs in the sample.

Learn more in

diagnosis of roundworm infection


Roundworm infections can usually be successfully treated with medication. Learn more in

treatment of roundworm infection


Regular hand washing can help prevent the spread of roundworm infection.

If you are travelling to a part of the world where roundworm is common, you should take additional precautions, such as drinking only bottled water and avoiding raw fruits and vegetables. These are the same precautions that help prevent many other infections associated with poor sanitation.

Learn more in

preventing roundworm infections

The bowels are the part of the digestive system between the stomach and the anus that digest and absorb food and liquid.

Signs of roundworm

In most people, a roundworm infection does not cause any noticeable symptoms.

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

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

Early-phase symptoms

The early-phase symptoms of a roundworm infection affect only a small proportion of those affected and are rare in the UK. They usually begin four to 16 days after swallowing the eggs and last up to 3 weeks. They include:

  • high temperature (fever) of 38C (100.4F) or above
  • a dry cough
  • shortness of breath
  • wheezing

Late-phase symptoms

If there are a lot of mature worms in the intestine they can cause blockages. This will not 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 abdominal (tummy) pain
  • nausea
  • vomiting
  • diarrhoea (you may also notice blood in your stools)

(Most people have no symptoms).

Signs and symptoms associated with an intestinal blockage due to a large number of worms include:

  • severe abdominal pain
  • vomiting

Causes of roundworm

A roundworm infection begins when you swallow roundworm eggs.

Eggs can be contained 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 your hands.

Contaminated soil or stools can also contaminate the water, making it possible to develop a roundworm infection by drinking contaminated water

The progress of roundworm infection

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 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’)

How is roundworm diagnosed?

A roundworm infection can be diagnosed by looking at a small stool sample under a microscope.

Infection can be confirmed by the presence of eggs or a worm in the sample.

A stool sample may be taken if:

  • you experience non-specific gastrointestinal symptoms, such as vomiting or diarrhoea, and you have been abroad within the last two years to a region where roundworm is widespread, such as Africa or Asia
  • you pass a worm in a stool (faeces). The worms have a distinct appearance which standard laboratories can recognise
  • worms are detected during diagnostic tests

Treatment for roundworm

Roundworm infection 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 one year of age.

Mebendazole works by stopping the roundworms from 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.

The most common side effect of mebendazole is stomach pain. Less common side effects include:

  • skin rash
  • diarrhoea
  • flatulence (excessive wind)


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

Side effects of piperazine can include:

  • abdominal (tummy) pain
  • nausea
  • vomiting
  • colic
  • diarrhoea

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

If your child is younger 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 that the manufacturer of the medicine has not applied for a license for albendazole to be used to treat roundworm in the UK. However, the medicine has been extensively studied in countries where roundworm is common and has been shown to be safe and effective.


While there is no firm evidence that any of the medications above can cause birth defects, they are not usually recommended during pregnancy. Roundworms may occasionally cause troublesome symptoms, but they do not usually pose a threat to your unborn child.

Preventing roundworm

Good hand hygiene can help prevent the spread of roundworm. But if you're travelling to a place where roundworm is common, you should take extra precautions.

Infection control

To prevent the spread of a roundworm infection, always wash your hands thoroughly:

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

Travel advice

You will 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, in particular 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 or Nigeria
  • South and Central America and the Caribbean
  • the Middle East

If you are travelling to these parts of the world:

  • Only drink bottled or boiled water.
  • Do not eat raw fruit or vegetables.
  • Wash your hands thoroughly if you come into contact with soil.
  • Whenever possible, eat hot food that has been thoroughly cooked.

See travel health and food and water abroad for more information and advice.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.