Toxocariasis is a rare infection caused by roundworm parasites (Toxocara). It is spread from animals to humans via their infected faeces.

The roundworm parasites live in the digestive system of dogs, foxes and cats. The worms range from 4cm to 12cm in length (1.5-5 inches).

The worms produce eggs, which are released in the faeces of infected animals and contaminate soil.

If someone accidently eats small particles of contaminated soil, they may develop toxocariasis. See Toxocariasis - causes for more information.

Types of toxocariasis

The symptoms of toxocariasis can vary depending on where in the body the infection occurs. There are three main types of toxocariasis:

• covert toxocariasis
• visceral larva migrans
• ocular larva migrans

Covert toxocariasis

Covert toxocariasis is the most common and mildest form of toxocariasis. Symptoms of covert toxocariasis include abdominal pain, a cough and headache.

Visceral larva migrans

Visceral larva migrans develops when large numbers of parasites spread through different organs of the body, such as the lungs, liver and heart.

The main symptoms of visceral larva migrans are fever, abdominal pain and shortness of breath.

Ocular larva migrans

Ocular larva migrans is the least common but potentially most serious type of toxocariasis. The condition can develop if the roundworm parasites move into the eyes.

The main symptoms of ocular larva migrans are blurred or cloudy vision and irritation of the eyes. Left untreated, ocular larva migrans can result in permanent vision loss, although only one eye is usually affected.

How common is toxocariasis?

Toxocariasis is an uncommon condition in this country. It is hard to estimate exactly how many cases of toxocariasis occur every year as the covert toxocariasis and visceral larva migrans forms of the condition often are misdiagnosed (or undiagnosed).

One researcher estimates that there are around 50 -100 cases of the ocular form of the condition each year in the UK.

However, many people have toxocara antibodies in their blood, which indicates that they have been exposed to the parasites.

Toxocariasis usually affects children aged between one and four years old. However, cases have been reported in people of all ages.

Young children are particularly at risk of getting toxicariasis because their play habits make them more likely to come into contact with contaminated soil, and many young children have a habit of eating soil.

Outlook

Treatment involves taking medication to kill the parasites. Most people will quickly make a full recovery and won't experience any long-term complications. See Toxocariasis - treatment for more information.

Due to advances in treatment, the potential risk of blindness is now a very rare complication of toxocariasis.

The symptoms of toxocariasis can vary depending on where in the body the infection occurs.

Most of the symptoms are caused by people having an allergic reaction to the larvae. In many cases, people are infected by the parasites but don't have any symptoms.

Covert toxocariasis is the most common and mildest form of the disease.

 Symptoms include:

• cough
• difficulty sleeping
• stomach pain
• headaches
• swollen lymph glands

Children with covert toxocariasis may also show a change in their usual behaviour, such as appearing unusually irritable.

Symptoms of visceral larva migrans

Depending on what parts (or organs) of the body are infected with parasites, visceral larva migrans can cause a wide range of possible symptoms. These may include:

• fatigue
• loss of appetite
• weight loss
• high temperature of 38ºC (100.4ºF) or above
• coughing
• breathing difficulties
• stomach pain
• headaches
• skin rashes
• swollen lymph glands
• seizures (fits)

Ocular larva migrans

Symptoms of ocular larva migrans include:

• blurred or cloudy vision that usually only affects one eye
• a very red and painful affected eye
• sensitivity to light 

Left untreated, it may result in permanent vision loss in the affected eye, although this is unlikely to happen.

Most cases of toxocariasis develop when someone handles contaminated soil and then transfers roundworm eggs into their mouth.

Soil becomes contaminated when an animal infected with the parasite (usually a dog, fox or cat) passes faeces that contain roundworm eggs into soil or sand. The eggs are produced in large numbers by the roundworm parasites that live in the animal's intestines.

The eggs have a tough outer shell and can survive for up to five years in sand or soil.

Once the eggs are inside the human body, they move into the person's bowel before hatching and releasing parasite larvae (the earliest stage of development). The larvae can travel to all parts of the body, but since humans aren't the normal host, the larvae don't develop into adults or invade the intestine.

See your GP if you have symptoms of toxocariasis.

A blood test can be taken to diagnose the infection.

If the parasites are present in your body, your immune system will produce a specific type of antibody that can be detected in your blood.

Antibodies

Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.

All three types of toxocariasis can be treated with a medication called an anthelminthic.

The most effective anthelminthic is albendazole, which is usually taken twice a day for five days. An alternative is mebendazole, which has to be taken for three to four weeks.

These medicines stop the parasites from being able to use glucose as food. Without a food source, the parasites will die.

The medicines don't usually cause side effects, although some people may have headaches at the start of their treatment.

Visceral larva migrans

In cases of visceral larva migrans that cause particularly severe breathing difficulties, admission to hospital may be required in order to support your breathing while the infection is treated.

In addition to anthelminthics, steriod medications are usually given to suppress the allergic reactions associated with heavy infections. 

Ocular larva migrans

In cases of ocular larva migrans, additional treatment may be required to prevent damage to the eye. For example, steroid medications can reduce eye inflammation and irritation.

In a number of cases, laser treatment is required to kill any parasites in the eye.

A type of treatment known as laser photocoagulation can be used to kill the parasites. Treatment is usually available on an outpatient basis, which means you won't have to stay in hospital overnight.

Drops are put into your eyes to numb the surface. A special contact lens is placed on your eye to hold your lids open and to focus the laser beam on to your retina. A laser is then used to burn away any parasites in your eyes.

Laser photocoagulation isn't usually painful, although you may feel an occasional sharp pricking sensation when certain areas of your retina are being treated.

Following treatment, your vision may be blurred. However, it should return to normal after a few hours.

Some people who've had laser photocoagulation experience some loss of peripheral vision (side vision) and night vision.

Inflammation

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Retina

The retina is the nerve tissue lining the back of the eye, which senses light and colour and sends it to the brain as electrical impulses.

Tissue

Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.

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 years 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.

Faeces

Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.