Toxocariasis

Toxocariasis (TOK-so-ka-RY-a-sis) is an infection that occurs in people, and most commonly affects young children who come in contact with contaminated dirt. It is caused by parasitic roundworms found in the intestines of cats and dogs.

What Is Toxocariasis?

Toxocariasis comes in two forms: visceral larva migrans (VIS-er-ul LAR-vuh MY-granz) and cutaneous larva migrans. Visceral larva migrans is a syndrome that usually results from infection with certain worms. Many cats and dogs, especially kittens and puppies, have intestinal worms called Toxocara canis (in dogs) or Toxocara cati (in cats). The culprit in visceral larva migrans is usually Toxocara canis and sometimes Toxocara cati. In rare instances, a pig roundworm called Ascaris suum or a raccoon round-worm called Baylisascaris procyonis may cause visceral larva migrans. This syndrome occurs when eggs from one of these worms pass with the stools from infected cats and dogs and then contaminate the soil. When children play in these contaminated areas, the eggs can stick to their hands or toys, and the children may then put their hands or the toys in their mouths and swallow the eggs. Those children who eat dirt are especially at risk. Adults may become infected, too, especially if they eat unwashed, contaminated vegetables.

When the eggs enter the digestive system, they hatch. The larvae burrow through the intestinal wall and move to the liver, lung, and sometimes to other sites, including the central nervous system, heart, kidney, and eye. (When it affects the eye, the syndrome is sometimes called ocular [OK-yoo-lur] larva migrans.) The larvae may stay alive for many months and cause damage to tissues or organs. Because the larvae are cat or dog parasites, they do not complete their life cycle in humans, so the larvae do not grow into egg-producing adults in humans.

Cutaneous larva migrans, which sometimes goes by the name of ground itch or creeping eruption, results from infection with various roundworm species, especially Ancylostoma braziliense, which occurs in dogs and cats in North Åmerica (usually from the central United States and South) and South America; Ancylostoma caninum, which affects dogs in Australia; and Uncinaria stenocephala, which affects dogs in Europe. In addition, people occasionally, although rarely, get cutaneous larva migrans from round-worms that occur in other animals, such as cows, horses, sheep, and goats. People can become infected when the larvae of these worms burrow into the skin. For instance, the larvae may infect the buttocks of a child who is sitting in contaminated dirt, or they may infect the bare feet of a beach-goer who is walking upon contaminated sand. A few days to a few months after they have burrowed into the skin, the larvae start to move beneath the skin, traveling an inch or more per day. Their movements are evident in red lines that appear on the skin. The larvac eventually reach and enter the bloodstream. From there, they typically travel to the lungs.

What Are the Symptoms of Toxocariasis?

Most people with visceral larva migrans have no symptoms. Those that do have symptoms may experience one or more of the following: fever, cough or wheezing, abdominal pain, enlarged liver or spleen, loss of appetite and weight loss, rash, and enlarged lymph nodes. Some patients may experience seizures or behavioral disorders, and in rare instances, an individual may die from heart, lung, or nerve problems associated with the syndrome. When an infection affects the eye, it can cause decreased vision, swelling around the eyes, and a cross-eyed appearance.