Toxocara are common parasites of dogs and cats. When they infect humans, the illness is called toxocariasis (or visceral larva migrans). Toxocariasis usually affects children under age 10. Especially at risk are children who like to put things in their mouths, or those whose families have pet dogs or cats.

Signs and Symptoms

Symptoms may include fever, cough or wheezing, abdominal pain, enlarged liver or spleen, poor appetite, a rash that sometimes looks like hives, and enlarged lymph nodes ("swollen glands").

Toxocariasis also may affect a child's eyes, causing decreased vision, swelling around the eyes, or a cross-eyed appearance. Untreated toxocariasis can cause retinal damage and decreased vision.

Most children with toxocariasis have no symptoms or only mild symptoms, and most cases are never diagnosed and do not cause problems. Some toxocariasis cases are diagnosed during a routine eye exam or an X-ray study done for some other reason.

Transmission

Toxocariasis is an infection caused by the larvae of parasitic worms - Toxocara canis and Toxocara cati - that usually live in the intestines of dogs and cats. Eggs from the Toxocara worms pass into the stools of dogs and cats and can contaminate pet areas around the home where children play. The eggs can be swallowed by children, especially those who:

• are 1 to 4 years old
• often put things in their mouths
• don't often wash their hands

Once Toxocara eggs enter a child's body, they hatch into larvae that penetrate through walls of the digestive tract and may migrate to a child's liver, lungs, eyes, and elsewhere.

Experts in the United States estimate that about 20% of dogs pass Toxocara eggs into their stool. In Great Britain, 24% of soil samples taken from public parks contained Toxocara eggs. Toxocariasis cannot be spread from person to person.

Prevention

You can help prevent your child from being exposed to toxocariasis by:

• keeping your child away from areas where dogs or cats play
• washing your toddler's hands frequently
• reminding your older child to wash his or her hands often, especially after playing with a pet dog or cat
• discouraging your toddler from putting dirty hands in his or her mouth
• keeping pets away from your child's sandbox and covering the sandbox when it's not being used
• taking household pets to the veterinarian to be dewormed, especially puppies younger than 6 months old

Diagnosis and Treatment

A doctor can usually diagnose a case of toxocariasis by physical exam and blood tests. Doctors may not prescribe any medication to treat a child with mild symptoms of toxocariasis. Severe toxocariasis involving the lungs, eye, or other important organs may be treated with antiparasitic drugs to kill the Toxocara larvae. For severe lung toxocariasis, doctors sometimes also prescribe anti-inflammatory drugs.

If your child has severe toxocariasis, give him or her medicine as prescribed by your doctor. You can prevent your child from becoming reinfected by deworming your pets and by keeping your child away from areas where pets defecate (poop). Remind your child to wash his or her hands often during the day, especially after playing with pets.

When to Call Your Child's Doctor

Call your child's doctor if your child has any of the symptoms of toxocariasis, including:

• fever
• rash
• cough or wheezing
• abdominal pain
• poor appetite
• vision problems

It's especially important to be watchful for these signs if your child often plays with pet dogs or cats, visits public parks, plays in sandboxes, or likes to put things in his or her mouth.

Reviewed by: Joel Klein, MD
Date reviewed: August 2005