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Toxocariasis Content Supplied by NHS Choices

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.

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.

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 parasite larvae.

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.

If toxocariasis has affected the eye, steroid medication is used instead of anthelmintics. 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.

Preventing toxocariasis

Practising good hygiene can help prevent toxocariasis.

Some of the steps you can take are listed below:

  • Wash your hands well with soap and warm water after handling pets or coming into contact with sand or soil.
  • 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.
  • Try to avoid letting children play in areas where there's a lot of dog or cat faeces.
  • Teach children that it's dangerous to eat dirt or soil.

Read more information about food safety and how to prevent germs from spreading.

Advice for 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 from birth, as a pregnant dog can pass the parasites to her puppies before they're born.

All dogs and cats require regular de-worming with anti-worm medicine. See your vet for regular check-ups and for specific advice on how to treat your pet.

The parasite eggs responsible for toxocariasis can survive for many months in sand or soil, so all pet faeces should be collected and disposed of in the garbage. There's no immediate danger from fresh faeces, as the eggs only become infectious after a few weeks.

Pets should be kept away from children's sandpits, which should be covered when not in use.

Your pet's living area should be cleaned at least once a week.

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 toxocariasis.