Young children can acquire the infection when they eat soil contaminated with animal stool (feces) that contain the roundworm eggs.
The infection may cause fever, cough or wheezing, and an enlarged liver, and in some people, 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.
(See also Overview of Parasitic Infections.)
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, but they can remain alive in the body for many months. The larvae require another host for maturation: dogs, cats, or other animals.
Toxocara eggs may be ingested by other mammals, such as rabbits or sheep. In these animals, the eggs hatch into larvae, which penetrate the wall of the intestine and travel to various tissues where they form cysts. Rarely, people are infected by eating raw or undercooked meat from these animals.
Toxocariasis symptoms may start within several weeks after eggs are ingested. They vary depending on the organ affected. Fever, cough or wheezing, and liver enlargement are the most common. Some people have a rash, spleen enlargement, or recurring pneumonia. They may lose their appetite.
When larvae infect the eye (usually only one eye), they typically cause no symptoms or very mild symptoms. However, the eyes may become inflamed, and vision may be impaired or lost.
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 of toxocariasis is confirmed by identifying Toxocara antibodies in the blood. (Antibodies are proteins produced by the immune system to help defend the body against attack, including that by parasites.)
Rarely, a sample of liver or other tissue is obtained and examined (biopsied) for evidence of larvae or inflammation resulting from their presence.
In most people with toxocariasis, the infection resolves on its own, and treatment is unnecessary. Albendazole or mebendazole plus corticosteroids is given when symptoms are severe or the eyes are infected. Eye specialists should be involved in the care of ocular larva migrans because of their expertise in the diagnosis and treatment of infections inside the eye. Even with appropriate care, most people have some loss of vision.
Occasionally, laser photocoagulation (application of an intense beam of light) is used to kill larvae in the eyes. Sometimes, doctors use cold probes (cryosurgery) or surgery.