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Toxocariasis is an infection caused by the ingestion of larvae of the dog roundworm Toxocara canis or the cat roundworm Toxocara cati. The soil of parks and playgrounds is commonly contaminated with the eggs of T canis, and infection may cause human disease that involves the liver, heart, lung, muscle, eye, and brain.

Three syndromes of Toxocara infection are generally recognized.

• In children, covert toxocariasis is a mild, subclinical, febrile illness. Symptoms can include cough, difficulty sleeping, abdominal pain, headaches, and behavioral problems. Examination may reveal hepatomegaly, lymphadenitis, and/or wheezing.
• Visceral larva migrans is caused by the migration of larvae through the internal organs of humans and the resulting inflammatory reaction. A constellation of symptoms develops, including fatigue, anorexia, weight loss, pneumonia, fever, cough, bronchospasm, abdominal pain, headaches, rashes, and, occasionally, seizures. Examination may reveal hepatomegaly, lymphadenitis, and/or wheezing. Occasionally, pleural effusions develop. Chronic urticaria has been described. Severe cases can lead to myocarditis or respiratory failure.
• Ocular larva migrans, which is caused by migration of larva into the posterior segment of the eye, tends to occur in older children and young adults. Patients may present with decreased vision, red eye, or leukokoria (white appearance of the pupil). Granulomas and chorioretinitis can be observed in the retina, especially at the macula. Unilateral visual loss, retinal fibrosis, retinoblastoma, and retinal detachment occur. Serum antibodies to Toxocara are often absent or present in low titers.