Introduction 

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:

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.

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.

Read more about preventing toxocariasis.

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.

Read more about treating toxocariasis.

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.

Page last reviewed: 10/06/2015

Next review due: 10/06/2017