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Toxocariasis

 

Toxocariasis is an uncommon infection caused by parasites that are known as toxocara canis (from dogs) and toxocara cati (from cats). Theyare more commonly known as roundworms.

Toxocariasis is a zoonotic condition. Zoonotic conditions are spread from animals to humans.

The toxocara parasites live in the digestive system of dogs and foxes and cats. Parasite eggs can be released in the faeces of infected animals and contaminate soil. If someone accidently ingests small particles of contaminated soil, they may develop toxocariasis.

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 toxocara canis parasites move into the eyes.

The main symptoms of ocular larva migrans are disturbed 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 a rare condition, with an average of 10 cases occurring each year in England. As the disease is not notifiable in Ireland, we do not have any clear indication as to the number of cases here. However, it is likely to be as uncommon in Ireland as it is in England.

Toxocariasis usually affects children who are between one and four years old. However, cases of toxocariasis 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. Many young children also have a habit of eating soil.

Outlook

With treatment, the outlook for toxocariasis is very good. Treatment involves taking medication designed to kill the parasites. Most people will quickly make a full recovery and will not experience any long-term complications.

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

Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Faeces
Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.
Stomach
The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.
Swelling
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.
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.

Toxocariasis is spread in the faeces (stools) of infected dogs and cats. To prevent the spread of the infection, dog-owners should always dispose of dog and cat faeces in a responsible way. 

Covert toxocariasis

The symptoms of covert toxocariasis include:

  • cough
  • difficulty sleeping
  • abdominal pain,
  • headaches
  • swollen lymph nodes (glands)

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

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 (fever) of 38C (100.4F) or above
  • coughing
  • breathing difficulties
  • abdominal pain
  • headaches,
  • skin rashes
  • swollen lymph nodes
  • seizures (fits), which are less common

Ocular larva migrans

Symptoms of ocular larva migrans include:

  • A disturbance (or reduction) in vision, such as blurred or cloudy vision that usually only affects one eye.
  • A very red and painful affected eye.
  • Light sensitivity (photophobia).
Allergic
An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.
Fever
A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37°C (98.6°F).
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.
Liver
The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.
Lungs
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
Lymph nodes
Lymph nodes are small oval tissues that remove unwanted bacteria and particles from the body. Part of the immune system.
Pain
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
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.    
Wheezing
Wheezing is the whistling sound made during breathing when the airways are blocked or compressed. 
 

The life cycle of toxocara canis

To better understand the causes of toxocariasis, it is useful to learn a little more about the life cycle of the toxocara parasites.

Adult parasites live in the small intestines of dogs and puppies (as well as a number of other mammals, such as foxes and cats). They range from 4-12cm in length (1.5-5 inches).

The adult parasites are capable of producing a large number of eggs. The eggs are passed out in the infected animal's stools (faeces).

The eggs have a tough outer shell and are able to survive for up to five years once they have been passed into the outside world.

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

Once the eggs are inside the human body, they move into the intestine before hatching and releasing parasite larvae (insects in their earliest stage of development). The larvae are capable of travelling to all parts of the body.

Most of the symptoms of toxocariasis are caused by people having an allergic reaction to the larvae. In many cases, people are infected by the parasites but do not experience any symptoms.

Abscesses
An abscess is a lump containing pus, which is made by the body during infection.
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.

 

Useful Links

A blood test can be used to diagnose toxocariasis. If you have the parasites 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.
Biopsy
A biopsy is a test that involves taking a small sample of tissue from the body so it can be examined.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Enzyme
Enzymes are proteins that speed-up and control chemical reactions, such as digestion, in the body.
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.
Liver
The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.

All three types of toxocariasis can be treated with a medication called mebendazole. Mebendazole stops the parasites from being able to use glucose as food. Without a food source, the parasites will die.

Most people are required to take a four-week course of mebendazole. Mebendazole does not usually cause side effects although some people may experience headaches at the start of their treatment.

Visceral larva migrans

In cases of visceral larva migrans that are causing particularly severe breathing difficulties, admission to hospital may be required so that your breathing can be supported while the infection is being treated.

Ocular larva migrans

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

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

A type of treatment that is known as laser photocoagulation can be used to kill the parasites. Treatment is usually available on an out-patient basis, which means that you will not 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 is not 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 have had laser photocoagulation experience some loss of peripheral vision (side vision) and night vision. One study found that more than 50% of people who were treated noticed some difficulty with their night vision, and 25% noticed some loss of their peripheral 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.

Useful Links

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 is 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 Toxocara worms before birth and both 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 years in soil or sand, so all dog and cat faeces should be collected and destroyed. Pets should be kept away from children's sandpits, which should be kept covered when they are not in use.

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

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.