Toxocariasis (visceral larva migrans) is infection caused by larvae of the roundworms Toxocara canis or Toxocara cati.

• Young children can acquire the infection when they eat soil contaminated with animal feces that contain the roundworm eggs.
• Most often, the infection causes fever, cough or wheezing, and an enlarged liver, but it may cause vision problems.
• Doctors confirm the diagnosis by identifying antibodies to the roundworm in a sample of blood.
• Regularly deworming dogs and cats can help prevent the infection.
• Treatment is usually unnecessary but may include antiparasitic drugs and corticosteroids.

Toxocariasis occurs mainly in young children, who acquire Toxocara eggs by ingesting soil contaminated by the feces of dogs, cats, or other animals that carry the parasite. Sandboxes, where dogs and cats often defecate, pose a particular hazard for exposure to the eggs. Children frequently transfer the eggs from their hands to their mouth and may eat the contaminated sand. Occasionally, adults ingest eggs picked up from contaminated soil, other surfaces, or hands and become infected. Adults and children who have a craving for nonfoods, such as soil or clay (a condition called pica), are at particular risk. After the eggs are swallowed, larvae hatch in the intestine. The larvae penetrate the intestinal wall and spread through the bloodstream. Almost any tissue of the body may be affected, but the liver and lungs are most commonly involved. The larvae can remain alive for many months, causing damage by moving through tissues and stimulating inflammation. The larvae do not mature to adulthood in people. They require an intermediate host for maturation: dogs, cats, or other animals.

Symptoms and Diagnosis

Symptoms may start within several weeks after eggs are ingested. Fever, cough or wheezing, and liver enlargement are the most common. Some people have a skin rash, spleen enlargement, or recurring pneumonia. When larvae infect the eyes, inflammation and decreased vision may result.

A doctor may suspect toxocariasis in a person who has an enlarged liver, inflammation of the lungs, a fever, and high levels of eosinophils (a type of white blood cell). The diagnosis is confirmed by identifying Toxocara antibodies in the blood. Rarely, a sample of liver or other tissue is obtained and examined (biopsied) for evidence of larvae or inflammation resulting from their presence.

Prevention and Treatment

Prevention involves deworming dogs and cats regularly. Covering sandboxes when not in use prevents animals from defecating in them. Pica and clay eating should be discouraged.

In most people with toxocariasis, the infection resolves on its own, and treatment is unnecessary. Albendazole or mebendazole plus corticosteroids are given when symptoms are severe or the eyes are infected. Occasionally, laser photocoagulation (application of an intense beam of light) is used to kill larvae in the eyes.

Last full review/revision March 2007 by Richard D. Pearson, MD