Visceral Larva Migrans

Epidemiology

  • Higher infection rates for children (especially boys and blacks), probably due to patterns of pica
  • Children are higher risk than adults for developing ocular or visceral forms of VLM

Etiology

  • Toxocara Canis (helminth: dog ascarid): dog infection (especially puppies) is common in temperate and tropical zones
    • ELISA for larval antigens show that 2.8% of dog population in USA is infected
  • Toxocara Cati (helminth: cat ascarid):

Physiology

  • Ingestion of soil contaminated by eggs (deposited by infected dogs or cats/ require weeks of incubation in soil) -> hatched larvae in intestine penetrate vessels -> travel to lungs -> travel to liver, brain, heart, muscle, eyes -> inflammatory response with necrosis, hemorrhage, granulomas
  • Infection may persist for up to 10 years in animal models
  • Life cycle is usually aborted at larval stage in adult dogs (but transplacental passage of larvae to puppies leads to fecal contamination of soil)

Diagnosis

  • Sputum GS/Cult+Sens:
  • Lung Bx: definitive diagnosis is finding of T. Canis larvae in tissue (but this is rarely possible)
    • May show granulomas with intact or fragmented larvae
  • CXR/Chest CT patterns (CXR is abnormal in 40% of cases):
    • Alveolar infiltrates (>30% of cases): typically bilateral small peribonchial infiltrates (which may be migratory) > subsegmental or segmental infiltrates
  • Albumin: globulin ratio: decreased
  • Total IgG and total /IgM: increased
  • Isohemagglutinin titer: increased anti-A (>1:400)/ increased anti-B (>1:200)
    • Seen more commonly in Toxocara Canis infection than in other nematode infections
  • Ab to Toxocara Canis: present in 28.8% of asthmatic children (compared to 6.4% of non-asthmatic children)
  • ELISA larval stage antigens: following absorption to remove cross-reacting roundworm antigens, test is specific
  • CBC: marked eosinophilia (usually >30%/ eosinophilia present in almost all cases)/ leukocytosis
  • Skin testing: not useful
  • Stool exam: not useful (since organism does not mature to reproductive stage in human)
  • Liver Bx: definitive diagnosis is finding of T. Canis larvae in tissue (but this is rarely possible)
    • May show granulomas with intact or fragmented larvae

Clinical

Lung Involvement

  • Asthma, Bronchiolitis, or Pneumonia-Like Presentation
    • Cough and wheezing (present in 20-85% of cases)

GI Involvement

  • Hepatosplenomegaly:

Other

  • Fatigue
  • Weight loss
  • Irritability
  • Skin rashes

Adult Endemic VLM (reported in France):

  • Eosinophilia
  • Abdominal pain
  • Weakness
  • Rash
  • Pruritus
  • Dyspnea
  • Hypergammaglobulinemia

Treatment

  • Diethylcarbamazine (2 mg/kg TID x 7-10 days) or thiabendazole (25 mg/kg BID x 5 days): preferred treatments
  • Steroids: usually used in combination with an anti-helminthic

References

  • xxx