Toxocara Species

Diagnosis

Indications for Testing

  • Appropriate exposure and symptoms
  • Clinical diagnosis may be hampered by the inability to distinguish among parasitic infections
    • Baylisascaris procyonis, Fasciola hepatica, and Ascaris lumbricoides can also cause visceral larval migrans

Laboratory Testing

  • Toxocariasis antibody detection (CDC)
  • Nonspecific
    • CBC will demonstrate eosinophilia in 30% of the cases
  • Serology
    • IgG antibody testing indicates previous infection
      • Single titer testing cannot distinguish between past and current infection

Histology

  • Tissue biopsy of involved site may demonstrate larvae (diagnostic)

Differential Diagnosis

Clinical Background

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.

Epidemiology

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

Organism

  • 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
    • 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

Treatment

  • Treatment is required for myocardial, central nervous system, and pulmonary involvement

Prevention 

  • Deworming dogs and cats
  • Prohibiting dog excreta in parks and playground
  • Preventing pica in children

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Assess presence of eosinophilia

   
Toxocara Antibody IgG by ELISA 0099090
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Diagnose and confirm T. canis infection

Toxocara antibody titers in populations without clinical symptoms of visceral larval migrans vary dramatically; elevated titers alone cannot definitively establish diagnosis

Because antibody response varies depending on worm burden and location, a negative result does not necessarily rule out toxocariasis infection

If results equivocal, repeat testing in 10-14 days