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For further information, see CMDT Part 35-29: Toxocariasis

Key Features

Essentials of Diagnosis

  • Principally seen in young children

  • Most infections are asymptomatic

  • Liver and lungs most commonly involved organs

  • CNS infection is rare

  • Ocular larva migrans is distinct syndrome that occurs in children older than is typical for visceral larva migrans

General Considerations

  • Caused by the dog roundworm Toxocara canis or by the cat roundworm Toxocara cati

  • Rarely, Baylisascaris procyonis, a roundworm of raccoons, causes visceral larva migrans in humans

  • Humans are infected after ingestion of eggs in material contaminated by dog or other feces

  • With T canis, 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

Clinical Findings

Symptoms and Signs

  • Most infections are asymptomatic

  • Cough, fever, wheezing

  • Hepatomegaly, splenomegaly

  • Lymphadenopathy

  • Pulmonary infiltrates

  • Eosinophilia

  • Involvement of the CNS can occur rarely, leading to eosinophilic meningitis and other abnormalities

  • Ocular larva migrans presents with

    • Visual deficits

    • Pain

    • Retinal mass, which can be confused with retinoblastoma

  • Manifestations of B procyonis infection, although rare, are typically similar but more severe than those with T canis

Differential Diagnosis

  • Acute HIV infection

  • Infectious mononucleosis

  • Lymphoma

  • Malaria

  • Ascariasis

  • Chagas disease

  • Retinoblastoma


Laboratory Tests

  • Blood tests may show eosinophilia in patient with hepatomegaly or other signs of disease

  • Serologic tests may be helpful

  • ELISA against a group of excreted antigens has shown good sensitivity and specificity

  • Molecular assays can identify specific pathogens

Diagnostic Procedures

  • Diagnosis is confirmed by identification of larvae in a biopsy of infected tissue, usually performed when other diseases are suspected



  • Most patients recover without specific therapy

  • Antihelminthics or corticosteroids may be considered in severe cases

  • Although no drugs have been proved to be effective, the following have been used

    • Albendazole

    • Mebendazole

    • Diethylcarbamazine

    • Ivermectin

  • Albendazole (400 mg twice daily for 5 days) has been recommended as treatment of choice



  • Disease in humans is best prevented by periodic treatment of puppies, kittens, and nursing dog and cat mothers, starting at 2 weeks postpartum, repeating at weekly intervals for 3 weeks and then every 6 months

  • Prevent defecation by dogs and cats in areas where children play


  • Symptoms of the acute infection may persist for months but generally clear within 1–2 years

  • The ultimate outcome is usually good, but ...

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