Toxocara Species - Toxocariasis

Toxocariasis is caused by migration of the larvae from the roundworm Toxocara to organs and tissues. Toxocara larva migrans is the second most common helminthic infection in developed countries. Transmission is fecal-oral via the feces of infected dogs or cats. Parasites are not shed in the gastrointestinal tract, so diagnosis relies on serology or tissue examination.


Indications for Testing

  • Ocular involvement
    • Change in vision, eye inflammation or retinal damage in individual with potential for exposure to feces of infected dog or cat
  • Visceral involvement
    • Fever, fatigue, cough, wheezing in individual with potential for exposure to feces of infected dog or cat

Laboratory Testing

  • Toxocariasis antibody detection (CDC)
  • Nonspecific – CBC demonstrates eosinophilia in 30% of cases
  • Serology – IgG antibody testing
    • Indicates exposure
    • Cannot distinguish between past versus current infection
  • Clinical diagnosis may be hampered by inability to distinguish among parasitic infections that can also cause visceral larval migrans – Baylisascaris procyonis, Fasciola hepatica, and Ascaris lumbricoides


Biopsy and pathologist examination may provide definitive diagnosis.

Differential Diagnosis



  • Incidence – one of the most common parasitic infections worldwide
  • Age – usually children 
  • Transmission – ingestion of soil contaminated with embryonated Toxocara eggs


  • Toxocara species that infect humans are T. canis and T. cati
  • Ingested eggs hatch into larvae, travel across gut wall, and migrate to liver or lungs through lymphatic and circulatory systems
  • Larvae then spread from lungs to other organs, causing damage by their migration and induction of granulomatous lesions

Clinical Presentation

  • Visceral larval migrans (VLM)
    • Asymptomatic, with mild eosinophilia
    • Cutaneous symptoms common
      • Chronic prurigo, pruritus, and/or urticaria and eczema
      • Symptoms persist a year or more
    • Severe and potentially fatal symptoms 
  • Ocular larval migrans
    • Frequently asymptomatic
    • Acute eye lesions caused by penetration of larvae into eyes
    • Vision loss in affected eye
  • Neural larval migrans – fever, headache, seizures
  • Common larval migrans – similar to visceral larval migrans but less severe

ARUP Laboratory Tests

Aid in diagnosis of toxocariasis

If results equivocal, repeat testing in 10-14 days

Medical Experts



Marc Roger Couturier, PhD, D(ABMM)
Professor of Pathology (Clinical), University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories


Additional Resources