Ascariasis (roundworm)

About roundworm

Roundworm is a type of parasite. A parasite is something that grows, feeds off and lives on, or in you (the host). Roundworm is well adapted to living in the human body. You can become infected with roundworm if you swallow roundworm eggs in contaminated water, food or soil. The worms are white in colour, have a similar appearance to an earthworm and can grow to 35cm long. Roundworm eggs are too small for you to see.

Roundworm is the most common type of worm infection worldwide – it's thought to affect up to a third of the world's population. Anyone can become infected, but it mostly affects children between the ages of two and 10.

Roundworm infection is most common in Africa, Central and South-East Asia, and Central and South America – worldwide, around a billion people are thought to be infected. It’s rare in the UK – only about 12 people a year get it, and those people have often recently travelled to tropical or subtropical countries where sanitation and hygiene are poor.

Symptoms of roundworm

A roundworm infection doesn't usually cause any symptoms. However, if you do get symptoms, you may:

  • cough and wheeze
  • have difficulty breathing
  • have a fever
  • have abdominal (tummy) pain
  • feel sick or vomit
  • lose your appetite
  • have diarrhoea

These symptoms aren't always caused by roundworm but if you have visited a tropical country in the past one to two years and your symptoms last for more than 10 to 14 days, see your GP.

Generally, the more worms you're infected with, the worse your symptoms are likely to be.

Babies can get other symptoms of roundworm, such as colic (inconsolable crying with bouts of fussiness and irritability).

Complications of roundworm

If you get severely infected, you may get complications of roundworm. These can include the following.

  • If you have hundreds, or even thousands of adult worms living inside you, the worms may block your small bowel completely, cause pain in your abdomen and make you vomit. Depending on how severe your condition is, you may need an operation to clear the blockage.
  • Roundworms can also enter and block the bile duct from your liver, which can cause jaundice. This makes your skin and the whites of your eyes yellow. The worms may also block your pancreatic duct and cause inflammation in your pancreas (pancreatitis). This can cause pain around the upper part of your abdomen and back.
  • Children with severe roundworm may have vitamin A and vitamin C deficiencies and become malnourished, grow more slowly and find it hard to put on weight.

Worldwide, roundworm infection can cause anaemia, malnutrition and delayed intellectual development in children on a large scale.

Causes of roundworm

You can become infected with roundworm if you come into contact with water, food or soil that is contaminated with A. lumbricoides eggs. The eggs are particularly suited to the warm, moist soil of tropical and subtropical countries, and can live in this soil for several years. The eggs in the soil can then transfer to fruit and vegetables.

If you swallow A. lumbricoides eggs, they pass from your stomach and into your small bowel. Here, they hatch and develop into larvae. The larvae then travel through the wall of your bowel and enter your bloodstream. After one to seven days, the larvae reach your lungs. From here, they travel up your windpipe (trachea) to the back of your throat. You then swallow the larvae, which pass through your stomach and into your small bowel, where they develop into adult worms. The adult female worms produce eggs that pass out of your body in your faeces.

Diagnosis of roundworm

Your GP will ask about your symptoms and examine you. He or she will also ask you about your medical history. Let your GP know where you have travelled to in the past couple of years as this will help with their diagnosis.

If you have been to an area where roundworm is common within the last one to two years, your GP may ask you to give a sample of faeces (stool sample), which will be sent to a laboratory for testing. Roundworm is diagnosed by the presence of A. lumbricoides eggs or worms in your faeces.

If there is a chance your small bowel may be blocked by the worms, your GP will refer you to a hospital where you may have other tests, such as a chest or abdominal X-ray.

Treatment of roundworm


Your GP may prescribe medicines to treat roundworm. These work best against adult worms. Medicines for roundworm include:

  • mebendazole – you take this as a tablet, either as a single dose or as a smaller twice-a-day dose for three days
  • levamisole – this is an alternative tablet to mebendazole, which you take in a single dose
  • piperazine – this medicine comes as a sachet of powder that you stir into milk or water

Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

Hospital treatment

If the roundworm infection is very severe and your intestines become blocked, you may need to go to hospital. Your doctor will try to clear the blockage using liquid paraffin and the drug piperazine, which will kill the worms. You may also be given fluids through a tube into your veins to keep you hydrated. If the treatment doesn't work, you may need surgery to clear the blockage, but generally, this is only necessary for people in the developing world – nobody has needed to have surgery in the UK in recent years.

Prevention of roundworm

There are a number of precautions you can take to help reduce your risk of getting roundworm if you're planning to travel to, or live or work in, an affected area. It’s important to:

  • drink only bottled or boiled water
  • always wash your hands after coming into contact with soil
  • thoroughly wash, peel or cook fruit and vegetables to remove any contaminated soil
  • only eat freshly prepared food (preferably hot food) that has been cooked thoroughly

If you have a roundworm infection, always wash your hands after going to the toilet and before preparing food to help prevent spreading roundworm to other people.

Can I catch roundworm from my cat or dog?


No, but similar worms and parasites can be passed on from these animals.


Ascaris lumbricoides, the worm that causes roundworm, has evolved to live inside humans, but not in cats and dogs. However, roundworms similar to A. lumbricoides do live in cats and dogs.

An illness known as toxocariasis, for example, can be caused by dog roundworm larvae travelling through your body. This can cause fever, coughing and wheezing, or liver problems depending on where the larvae travel. Toxocariasis can cause more serious problems if the larvae reach your eyes or brain. If you do get infected, there are medicines available to kill the larvae.

Because of the risk of the animal form of roundworm infection, it's important to de-worm your pets regularly and to clean up their waste – always wash your hands thoroughly after you do so.

Can I spread roundworm directly to other people?


Yes, but indirectly.


Roundworm can't be spread directly from person to person, for example, through touch. It can only be spread through accidentally eating A. lumbricoides eggs from infected human faeces, or from contaminated food.

Going to the toilet outside and using human manure to fertilise crops are common ways that roundworm is spread, particularly in developing countries. Always dispose of nappies properly and wash your hands after using the toilet.

Are there any side-effects of the medicines for roundworm?


Yes. All medicines have the potential to cause side-effects, but most people don't have any or only have minor side-effects.


If you have roundworm and need treatment, you're unlikely to have any side-effects from the medicines.

Some people who take piperazine may feel sick, vomit or have diarrhoea. Also, people who take mebendazole may have abdominal (tummy) pain and less commonly, diarrhoea. Other more serious side-effects are rare (only one to 10 in 10,000 people get them).

Always ask your doctor for advice and read the patient information leaflet that comes with your medicine.