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Page last reviewed: 13/07/2011

Roundworms are worms that can infest the human digestive tract, specifically the small intestine. As the Latin name for roundworms is Ascaris lumbricoides, a roundworm infection is also sometimes known as ascariasis.

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

When symptoms do occur, they include a high temperature and dry cough 4-16 days after swallowing the eggs. You may have mild abdominal pain, vomiting and diarrhoea later on. See Roundworm - symptoms for more information.

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

How infection occurs

A roundworm infection can occur if someone swallows 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 and do not wash their hands before eating.

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.

How common are roundworm infections?

Roundworm infections are one of the most common health conditions in the world. It is estimated that 1.4 billion people (a quarter of the world's population) currently have 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.

It is estimated that the global distribution of cases of roundworm is as follows:

  • 75% of cases are in Asia and Oceania.
  • 17% of cases are in Africa and the Middle East.
  • 8% of cases are in Central and South America and the Caribbean.

Ascaris eggs thrive in warm, moist soil. Children are more likely to develop a roundworm infection than adults because they are more likely to come into contact with contaminated soil when playing.

The ascaris parasite is not native to Ireland. This means that any cases of roundworm recorded in Ireland were contracted abroad, either by travellers or migrants coming to Ireland from parts of the world where roundworm is present.


In Ireland, the outlook for people who are treated for a roundworm infection is excellent. A range of very effective medications can be used to kill the roundworm.

If a very 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.

However, in Ireland these types of roundworm complications are very rare.

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

The global impact of roundworm

Roundworms are a serious health problem in parts of the developing world. Many poorer people do not have access to healthcare so a roundworm infection can quickly become serious.

Another problem is that a roundworm infection can affect a child’s ability to absorb essential nutrients, such as iron, from their diet, which can lead to malnutrition and delayed physical growth.

Despite there being very effective medications to treat roundworm, the condition is still a significant cause of death in poorer and under-resourced communities. Estimates of the numbers of deaths caused by roundworm vary significantly, possibly because it is difficult to get accurate clinical data from the poorer parts of the world. Figures range from 10,000 to 100,000 deaths a year, most of which are in children.

Page last reviewed: 13/07/2011

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

It is unclear why some people are particularly sensitive to the effects of roundworms while most people are unaffected. One theory is that most people have a natural immunity (resistance) to roundworms, which prevents the parasites from reproducing and moving through the body.

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.
  • Late-phase symptoms are caused by larvae moving back from the lungs to the intestine, where they begin to reproduce (see Roundworm - causes for more information about the life cycle of the roundworm).

Early-phase symptoms

The early-phase symptoms of a roundworm infection usually begin 4 to 16 days after swallowing the eggs. They include:

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

Late-phase symptoms

The late-phase symptoms usually develop six to eight weeks after the eggs have been swallowed. The severity of your symptoms will depend on the number of roundworms inside your body. A low number of worms is known as a 'light worm burden' and a high number of worms is known as a 'heavy worm burden'.

Signs and symptoms associated with a light worm burden include:

  • mild abdominal (tummy) pain
  • nausea
  • vomiting
  • diarrhoea (you may also notice blood in your stools)

Signs and symptoms that are associated with a heavy worm burden include:

  • passing a worm in your vomit, stools or through one of your nostrils
  • severe abdominal pain
  • nausea
  • vomiting
  • feeling like you have a lump in your throat
  • unexplained weight loss

Blocked intestine

If your worm burden is particularly heavy, the worms can cause a blockage in your intestine. This is usually more common in children aged one to five years because their intestines are smaller and at greater risk of becoming blocked. Children between these ages account for 85% of cases of blocked intestine. 

The symptoms of blocked intestine include:

  • a severe, sharp abdominal pain
  • vomiting (the vomit may contain worms)
  • high temperature (fever) of 38C (100.4F) or above
  • diarrhoea

Page last reviewed: 13/07/2011

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.

Page last reviewed: 13/07/2011

A roundworm infection can be diagnosed by taking a small stool sample for examination under a microscope to see whether there are any eggs in the sample, or by identifying the worm itself.

In Ireland, roundworm is a relatively rare condition, so a stool sample will only be routinely taken if:

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

Page last reviewed: 13/07/2011

There are three main medicines used to treat roundworm infections. They 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 being able to make use of 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 a tablet of mebendazole 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 3-11 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 (abdominal pain caused by trapped wind)
  • 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.


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

However, there may be some circumstances where the benefits of treatment outweigh the potential risk, for example if you develop a blocked intestine or experience significant internal bleeding.

In such circumstances, mebendazole is thought to be the safest medication to use during pregnancy, although ideally treatment should be delayed until the second trimester (weeks 13 to 28 of pregnancy) or the third trimester (week 29 until birth). Using mebendazole during the first three months of pregnancy is thought to carry the highest risk of birth defects (although the risk is still thought to be low).

Page last reviewed: 13/07/2011

Infection control

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

  • after using the toilet
  • after changing a nappy
  • 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 the Health A-Z topic about Travel health

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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