Background

Several roundworm parasites found in domestic animals can infect humans. Parasites are usually found in the larval stages in human tissues and provoke the clinical condition referred to as larva migrans. Toxocara species, the ascarid of dogs and cats, is most commonly associated with larva migrans. Classic visceral larva migrans (VLM) typically occurs in preschool-aged children with a history of eating dirt. Children can present with severe infection and can suffer from seizures, myocarditis, and encephalitis. Death has also been reported in some cases.

Pathophysiology

Children contract Toxocara infections by ingesting embryonated eggs. The larvae hatch in the small intestine, invade the mucosa, and enter the portal system. The liver traps some larvae, but other larvae proceed to the lungs and the circulatory system, where they can disseminate to virtually every organ. In particular, the larvae often deposit in the liver, lungs, eye, heart, and brain. However, the parasite cannot complete its life cycle in humans. Larvae persist in tissues, provoking a granulomatous reaction and eventually dying. As a result, abscesses or granulomas form. Clinical manifestations depend on the tissue damage caused by the invading larvae and the associated immune-mediated inflammatory response.

See the image below.

Diagram of the Toxocara canis life cycle image. Courtesy of the Centers for Disease Control and Prevention.

Frequency

United States

The seroprevalence of Toxocara infection in children varies from 2-10%.

International

Although most reported cases occur in the United States, international incidence is likely similar or slightly higher.

Mortality/Morbidity

Death is rare. Long-term morbidity is present with ocular larva migrans (ie, loss of vision in the affected eye) but not usually with visceral larva migrans. Chronic eosinophilic pneumonia, myocarditis, and Henoch-Schönlein purpura have been associated with visceral larva migrans.

Race

Infection rates are higher among blacks and Hispanics, likely because of greater exposure to the parasite.

Sex

Visceral larva migrans has no sex predilection.

Age

Infection primarily occurs in children aged 1-4 years but can occur at any age.

Clinical Presentation

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