Paper I
Question
Larva migrans
Answer
Larva migrans: a clinical syndrome caused by the migration of larvae of animal (non-human) parasitic nematodes through human tissue, where the human is an accidental, dead-end host (the larvae cannot complete their life cycle/mature in humans).
Types:
- Cutaneous larva migrans (“creeping eruption”) — caused most commonly by the larvae of animal hookworms, particularly Ancylostoma braziliense (dog/cat hookworm); larvae penetrate exposed skin (commonly the feet, from walking on contaminated sand/soil) and migrate through the epidermis, producing an intensely pruritic, serpiginous, raised, erythematous tunnel-like track that advances a few millimetres to centimetres per day, since the larvae lack the collagenase needed to penetrate the basement membrane and invade deeper tissue.
- Visceral larva migrans — caused most commonly by the larvae of Toxocara canis (dog roundworm) or Toxocara cati (cat roundworm); ingested eggs hatch in the human intestine, and larvae migrate through the viscera (liver, lungs, eyes, CNS), causing eosinophilic granulomatous reactions, hepatomegaly, pulmonary symptoms (cough, wheeze), and, notably, ocular involvement (ocular larva migrans, which can mimic retinoblastoma).
Diagnosis: largely clinical for cutaneous larva migrans (characteristic serpiginous track); for visceral larva migrans — marked peripheral eosinophilia, elevated total IgE, and serology (ELISA for Toxocara excretory-secretory antigen).
Treatment: Albendazole or Ivermectin (for cutaneous larva migrans); Albendazole or Diethylcarbamazine with corticosteroid cover for visceral larva migrans (to control the inflammatory response to dying larvae).