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Diseases Transmitted by Pets: Toxocariasis

When common parasites of dogs and cats infect humans, the illness is called toxocariasis.

May 24, 2018 4 min read
Diseases Transmitted by Pets: Toxocariasis


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

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 can look like hives
  • enlarged lymph nodes ("swollen glands")

Toxocariasis also may affect the eyes, causing decreased vision, swelling around the eyes, or a cross-eyed appearance, and retinal damage if left untreated. Most cases go undiagnosed and do not cause any major problems. Some toxocariasis cases only have a positive diagnosis during a routine eye exam or an X-ray study done for some other medical reason.


Toxocariasis is an infection caused by the larvae of the parasitic worms (Toxocara canis and Toxocara cati), both usually living in the intestines of dogs and cats. Cats are normally the only hosts of Toxocara cati, and dogs are normally the only hosts of Toxocara canis. Eggs from the worms pass into the feces of dogs and cats, and can contaminate pet areas around the home where kids play.

Children, especially those who are 1 to 4 years old, who often put things in their mouths and don't often wash their hands, are at risk for swallowing the eggs. After entering the body, the eggs hatch into larvae, which penetrate the walls of the digestive tract where they 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 will not transmit from person to person, although humans are the "accidental hosts" of Toxocara; this is why it is apparent throughout the world rather than only in certain countries. Most cases of toxocariasis appear in people under the age of twenty.

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To help prevent kids from toxocariasis exposure, you can do the following:

  • keep children away from areas where dogs or cats play
  • wash your toddler's hands frequently
  • remind older kids to wash their hands often, especially after playing with a pet dog or cat
  • discourage toddlers from putting dirty hands in their mouth; this is a good idea even in a household without pets!
  • keep pets away from the kids' outdoor sandbox and cover the sandbox when it's not being used
  • take household pets to the veterinarian to be de-wormed, 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 require anti-parasitic drug treatment to kill the larvae. For severe lung toxocariasis, doctors sometimes also prescribe anti-inflammatory drugs.

A child with severe toxocariasis needs medicine as prescribed by your doctor. Prevent re-infection by de-worming 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 following symptoms of toxocariasis, including:

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

Toxocariasis will often resolve itself, because the Toxocara larvae cannot mature within human hosts. A corticosteroid prescription it the typical treatment in severe cases.



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