What Is Toxocariasis?

Toxocariasis (tox-oh-keh-RYE-eh-sis) is a human infection caused by a type of worm that can live in the intestines of dogs and cats. It is most common in young children and pet owners, but anyone can get it.

What Causes Toxocariasis?

Eggs from the dog worm Toxocara canis or the cat worm Toxocara cati pass into their feces (poop). The eggs can last a long time in the soil of yards, parks, and playgrounds. People can swallow these eggs if there's contaminated dirt on their food or hands. This happens more in kids, who don't always wash their hands well or often enough, and who like to put their hands in their mouths.

Rarely, people can get infected by eating undercooked meat that contains Toxocara larvae (baby worms).

What Happens in Toxocariasis?

Swallowed eggs pass into the intestines, where they hatch into larvae. The larvae go through the intestinal wall and enter the bloodstream. Then, they travel to other body parts, such as the liver, lungs, heart, brain, or muscles.

The larvae don't grow into intestinal worms in humans as they do in dogs or cats. But they can live for months or even years in a human, and can damage whatever organ they have infected.

What Are the Signs & Symptoms of Toxocariasis?

Many people with toxocariasis don't have any symptoms. If symptoms do happen, they can range from mild to severe.

Symptoms depend on what part of the body is affected, and can include:

  • fever
  • coughing or wheezing
  • belly pain
  • an enlarged liver
  • loss of appetite
  • a rash that sometimes looks like hives
  • enlarged lymph nodes ("swollen glands")
  • vision problems. The eye can be red and painful, the eyes can look crossed, or vision can get blurred or cloudy. If not treated, it can lead to blindness in the affected eye.

How Is Toxocariasis Diagnosed?

Because kids don't always have symptoms, many cases of toxocariasis aren't diagnosed. If symptoms happen, doctors will do an exam and order blood tests and, sometimes, other tests.

How Is Toxocariasis Treated?

A child with mild symptoms might not need treatment because the infection will go away on its own when the larvae die. Kids with symptoms that affect the lungs, eye, or other important organs may be treated with anti-parasite drugs that will kill the larvae.

Doctors sometimes also give steroids to ease inflammation in the damaged organs. They also might refer a child to a specialist (like an ophthalmologist if the eye is involved).

Can Toxocariasis Be Prevented?

To help protect your kids from exposure to the eggs or larvae that cause toxocariasis:

  • Take your pets to the veterinarian to be dewormed, especially puppies younger than 6 months old.
  • Clean and disinfect your pet's living area often and wash your hands well after. 
  • Everyone in the family should wash their hands well after playing with pets or other animals, after playing outside, and before touching or eating food.
  • Teach young children not to put dirty hands in their mouth and not to eat dirt or soil.
  • Keep kids away from areas with pet and animal poop.
  • If you have a sandbox, keep pets away from it and cover it when it's not in use.
  • Wash, peel, or cook all fruits and vegetables before eating them.
  • Cook meat well before eating it.
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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.