35-29: Toxocariasis

The dog roundworm Toxocara canis, the cat roundworm Toxocara cati, and less commonly other helminths may cause visceral larva migrans. T canis is highly prevalent in dogs. Humans are infected after ingestion of eggs in material contaminated by dog or other feces. Infection is spread principally by puppies and lactating females, and the eggs must be on the ground for several weeks before they are infectious. After ingestion by humans, larvae migrate to various tissues but cannot complete their life cycle.

Visceral larva migrans is seen principally in young children. Most infections are asymptomatic. The most commonly involved organs are the liver and lungs. Presentations include cough, fever, wheezing, hepatomegaly, splenomegaly, lymphadenopathy, pulmonary infiltrates, and eosinophilia. Involvement of the CNS can occur rarely, leading to eosinophilic meningitis and other abnormalities. Ocular larva migrans is a distinct syndrome, usually in children older than is typical for visceral larva migrans. Children present with visual deficits, pain, and a retinal mass, which can be confused with retinoblastoma. Baylisascaris procyonis, a roundworm of raccoons, can rarely cause visceral larva migrans in humans, typically with similar, but more severe manifestations than T canis.

The diagnosis of visceral larva migrans is suggested by the finding of eosinophilia in a child with hepatomegaly or other signs of the disease, especially with a history of exposure to puppies. The diagnosis is confirmed by the identification of larvae in a biopsy of infected tissue, usually performed when other diseases are suspected. Serologic tests may be helpful; an ELISA against a group of excreted antigens has shown good sensitivity and specificity. Molecular assays can identify specific pathogens. Most patients recover without specific therapy, although symptoms may persist for months.

Treatment with antihelminthics or corticosteroids may be considered in severe cases. No drugs have been proven to be effective, but albendazole (400 mg orally twice daily for 5 days), mebendazole, diethylcarbamazine, and ivermectin have been used, and albendazole has been recommended as the treatment of choice.