Toxocariasis is a rare infection caused by roundworm parasites. It's spread from animals to humans through contact with infected faeces.

Roundworm parasites are most commonly found in cats, dogs and foxes, and usually affect young children.

This is because children are more likely to come into contact with contaminated soil when they play and put their hands in their mouths.

However, cases have been reported in people of all ages.

Signs and symptoms

For most people, an infection with these roundworm larvae causes no symptoms and the parasites die within a few months.

However, some people experience mild symptoms, such as:

  • a cough
  • a high temperature (fever) of 38C (100.4F) or above
  • headaches
  • stomach pain

In rare cases, the roundworm larvae infect organs such as the liver, lungs, eyes or brain and cause severe symptoms, such as:

  • fatigue
  • loss of appetite or weight loss
  • skin rashes
  • wheezing or breathing difficulties
  • seizures (fits)
  • blurred or cloudy vision, usually only affecting one eye
  • a very red and painful eye

When to see your GP

See your GP as soon as possible if you think you or your child have symptoms that may be caused by toxocariasis.

If one of your eyes is affected by toxocariasis, there's a risk of permanent vision loss. However, prompt treatment can reduce the chances of this happening.

A blood test can usually detect toxocariasis, although you may need an eye examination to look for parasites if your eyes are affected.

Why it happens

The roundworm parasites responsible for toxocariasis (called Toxocara) live in the digestive system of dogs, cats and foxes. The worms produce eggs, which are released in the faeces of infected animals and contaminate soil.

The eggs only become infectious after 10-21 days, so there's no immediate danger from fresh animal faeces. However, once the eggs are passed into sand or soil, they can survive for many months.

Humans can become infected if contaminated soil gets into their mouth. Once the eggs are inside the human body, they move into the bowel before hatching and releasing larvae (the earliest stage of development). These larvae can travel to most parts of the body.

However, as humans aren't the normal host for these larvae, they can't develop beyond this stage to produce eggs. This means that the infection can't spread between humans.

Reducing your risk

The best way to reduce the chances of developing toxocariasis is to practise good hygiene.

For example, washing hands with soap and warm water after handling pets or coming into contact with sand or soil.

If you have a pet cat or dog, they should be regularly de-wormed and their faeces should be disposed of immediately.

How it's treated

If you have no symptoms, or only mild symptoms, treatment isn't usually necessary.

However, you'll need medication if you have a severe infection affecting your organs. A type of medication called an anthelmintic is used to kill the parasites.

If your eye is affected by toxocariasis, anthelmintics aren't used, but steroid medication (corticosteroids) may be required to suppress inflammation. Surgery may also be needed – for example, if you develop retinal detachment.

Most people make a full recovery and don't experience any long-term complications. However, there's a risk of permanent vision loss if one of the eyes is affected.

How common is toxocariasis?

Toxocariasis is rare in the UK, although it's hard to determine exactly how many cases occur every year, as the condition is often misdiagnosed or undiagnosed. Many people are likely to have been exposed to the parasites without knowing it.

In general, toxocariasis is more common in children and young adults.


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For most people, treatment for toxocariasis isn't needed, as the condition often improves on its own.

Treatment is usually only needed in severe cases, where the infection causes organ damage.

Medication is the main treatment in these cases. You can usually be treated at home, but you may need to be admitted to hospital if your symptoms are particularly severe.


A type of medication called an anthelmintic is the main treatment for severe cases of toxocariasis. These medicines kill the parasite larvae responsible for the infection.

Albendazole is most often used and mebendazole is an alternative.

These medicines don't usually cause side effects, although some people may experience headaches or stomach pain.

In addition to anthelmintics, steroid medications (corticosteroids) are often given to reduce any inflammation caused by a severe infection.

Steroid medication is used instead of anthelmintics for toxocariasis affecting the eye.


Surgery may be recommended in severe cases of toxocariasis where one of your eyes is infected.

The main types of surgery used include:

  • vitrectomy – where the jelly-like substance that fills the inside of the eye is removed and replaced with a gas or liquid substitute
  • laser photocoagulation – where a laser is used to kill the parasites in the eye

Both these techniques can be carried out using local anaesthetic eye drops to numb your eye and the surrounding area.

Like all surgical procedures, these techniques carry a risk of complications. For example, there's a risk of some degree of permanent vision loss (such as reduced side and night vision). However, the risk of total vision loss in the infected eye from toxocariasis usually outweighs the risk of surgical complications.

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Practising good hygiene can help prevent toxocariasis.

Some of the steps you can take are listed below.

  • Wash your hands well with soap and water after handling pets or coming into contact with soil or sand.
  • Teach children to always wash their hands after playing with dogs or cats, after playing outdoors and before eating.
  • Wash food that may have come into contact with soil.
  • Don't allow children to play in areas that are covered in dog or cat faeces.
  • Teach children that it's dangerous to eat dirt or soil.

Pet owners

Parents and children should be aware of the dangers associated with puppies, kittens and older dogs and cats.

Many puppies are infested with the roundworm parasites shortly after birth. Puppies and kittens require de-worming with anti-worm medicine. This should be given at two, three, four and eight weeks after birth, twice more between three and six months of age, and then on one final occasion. Pregnant bitches should be treated with the same medicine. See your vet for specific advice on how to treat your pet.

Clean your pet's living area at least once a week. Faeces should be either buried or bagged and disposed of in the dustbin.

Toxocara eggs can survive for many months in soil or sand, so all dog faeces should be collected and destroyed. Pets should be kept away from children's sandpits, which should be kept covered when not in use.

Some areas within public parks in the UK have been set aside as designated dog exercise areas. Dog owners should ensure that their dogs use these areas to minimise the risk of other park users getting a toxocariasis infection.

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Selected links

NHS Direct Wales links


External links

Health Protection Agency

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The information on this page has been adapted by NHS Wales from original content supplied by NHS Choices.
Last Updated: 29/07/2015 10:56:47