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

Signs and Symptoms

Many kids won't have symptoms, but if they do, they can 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 the eyes, causing decreased vision, swelling around the eyes, or a cross-eyed appearance. Untreated toxocariasis can cause retinal damage and decreased vision.

Most cases go undiagnosed 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.


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 worms pass into the feces of dogs and cats and can contaminate pet areas around the home where kids 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

After entering the body, the eggs 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 the eggs. Toxocariasis cannot be spread from person to person.


To help prevent kids from being exposed to toxocariasis:

  • keep them away from areas where dogs or cats play
  • wash your toddler's hands frequently
  • reminding older kids to wash their hands often, especially after playing with a pet dog or cat
  • discouraging toddlers from putting dirty hands in their mouth
  • keeping pets away from the 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. Severe toxocariasis involving the lungs, eye, or other important organs may be treated with antiparasitic drugs to kill the larvae. For severe lung toxocariasis, doctors sometimes also prescribe anti-inflammatory drugs.

A child with severe toxocariasis should be given medicine as prescribed by your doctor. Prevent reinfection by deworming your pets and keeping kids away from areas where pets defecate (poop). Remind your kids to wash their hands often during the day, especially after playing with pets.

When to Call the Doctor

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

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

Reviewed by: Joel Klein, MD
Date reviewed: September 2011

Kids Health

Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

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