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”)

Roundworms can infest the human gut, where they live, feed and reproduce. They don’t often cause any symptoms, but are more likely to in large numbers.

A roundworm infection – also sometimes known as ascariasis or ascaris – is usually easy to treat.

Roundworms are parasites. They use the human body to stay alive, feed and reproduce.

A roundworm infection doesn’t usually cause any noticeable symptoms. People usually see their GP because they’ve seen a worm in their stools (faeces).

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. However, in England, these types of complications are rare.

Read more about the symptoms of a roundworm infection.

How infection occurs

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

It’s also possible for eggs to be transferred from your hands to your mouth after touching 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 there are inside your body, the worse your symptoms are likely to be.

Read more about the causes of a roundworm infection.

Diagnosing a roundworm infection

See your GP if you notice a roundworm in your faeces or you have unexplained asthma-like symptoms shortly after visiting a tropical or sub-tropical country.

A roundworm infection can be diagnosed by examining a small sample of faeces under a microscope. Infection is confirmed by the presence of eggs or a worm in the sample.

Roundworm is a relatively rare condition in the UK, so a stool sample will only be routinely taken if:

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

Treating a roundworm infection

Roundworm infections can usually be successfully treated with medication.

The three main medicines that are used to treat an infection are:

• mebendazole
• piperazine
• albendazole

Read more about these medicines in treating a roundworm infection.

Preventing a roundworm infection

Regularly washing your hands can help prevent the spread of a roundworm infection.

You should take additional precautions if you’re travelling to a part of the world where roundworm is common, such as only drinking bottled water and avoiding raw fruit and vegetables.

These are the same precautions that help prevent many other infections associated with poor sanitation.

Read more about preventing roundworm infections.

Bowels

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

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.

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:

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

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.

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

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:

• skin rash
• diarrhoea 
• flatulence (excessive wind)

Piperazine

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

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.

Pregnancy

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.