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

• Pulmonary symptoms
  • Asthma
  • Other helminthic infections
  • Eosinophilic pneumonia
  • Churg-Strauss syndrome
  • Allergic bronchopulmonary aspergillosis
• Ocular
  • Granulomatous diseases such as M. tuberculosis, sarcoidosis
• Dermatologic symptoms
  • Dermatitis
  • Hot tub folliculitis
  • Skin infections – bacterial
  • Schistosomal dermatitis
  • Other helminthic diseases – strongyloides, loiasis

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 
    • Hepatosplenomegaly
    • Hypergammaglobulinemia
    • Fever
    • Pneumonitis
      • Wheezing, dyspnea
      • May manifest as transient migratory infiltrates on chest x-ray
    • Neurological disorders
      • Neurologic disease
        • Very uncommon
        • May manifest with headache, myelitis, eosinophilic meningitis/encephalitis, seizures
• 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