Describe cutaneous and visceral larva migrans with their causes and management.

Cutaneous Larva Migrans

• Man is a dead-end host. The larva lacks the collagenase needed to penetrate the human basement membrane, so it is trapped in the epidermis and wanders aimlessly until it dies after weeks to months
• Acquired by skin contact with soil or sand contaminated by dog or cat faeces — classically on beaches, and on the feet, buttocks and back of those who sit or lie on contaminated ground
• Clinical features — an intensely itchy, serpiginous, raised, erythematous track advancing a few millimetres to a couple of centimetres per day, with vesiculation and secondary bacterial infection from scratching. The itch is often severe enough to prevent sleep
• The diagnosis is clinical; biopsy is unhelpful because the larva lies ahead of the visible track and is usually missed
• Treatment — ivermectin as a single dose, or albendazole for 3 days; topical thiabendazole for limited lesions. It is self-limiting but treatment relieves severe symptoms promptly
• Prevention — footwear, avoiding sitting directly on damp sand or soil, using a mat or towel, deworming pets and excluding dogs from beaches and playgrounds

Visceral Larva Migrans (toxocariasis)

• Caused by toxocara canis (dog) and T. Cati (cat), whose eggs are ingested from soil contaminated with animal faeces. Again man is an accidental dead-end host
• Affects young children with pica, and those in close contact with puppies; playgrounds and sandpits are a recognised source, and eggs survive in soil for years
• The larvae hatch, penetrate the gut and migrate through the tissues — liver, lung, muscle, eye and brain — but cannot mature, so they wander and eventually die, provoking eosinophilic granulomas
• Visceral larva migrans — fever, hepatomegaly, cough and wheeze, with marked and persistent eosinophilia (often above 30%), leucocytosis and hypergammaglobulinaemia. It is a recognised cause of prolonged unexplained eosinophilia in a child
• Ocular larva migrans — a single larva reaching the eye produces a retinal granuloma, usually in an older child with little or no eosinophilia, causing unilateral visual loss, strabismus or leukocoria. It is characteristically mistaken for retinoblastoma, and has led to unnecessary enucleation
• Covert toxocariasis — non-specific abdominal pain, cough and wheeze with eosinophilia; and an association with asthma and with epilepsy
• Diagnosis — serology by ELISA for Toxocara excretory-secretory antigen, since the larva never matures and NO eggs are ever passed — so stool examination is always negative. Ocular disease may need aqueous or vitreous antibody
• Treatment — albendazole with corticosteroids to contain the inflammation caused by dying larvae; ocular disease is managed with steroids, laser and vitrectomy, since killing a larva in the eye is itself damaging

Other Migrating Larvae and Applied Aspects

• Consider toxocariasis in a child with unexplained persistent eosinophilia, and ask about pica and about puppies; the stool will be negative and only serology will establish it
• Do not enucleate for suspected retinoblastoma without considering ocular toxocariasis; the distinction is made by serology, imaging and the clinical context, and the consequence of error is the loss of a healthy eye
• Deworm pets regularly, particularly puppies and kittens, which carry the heaviest burdens; and dispose of animal faeces properly
• Cover sandpits and exclude dogs from playgrounds; Toxocara eggs persist in soil for years and are the reason these measures exist
• The speed of the track distinguishes the two creeping eruptions — centimetres per day in cutaneous larva migrans, centimetres per hour in larva currens, and the latter demands treatment for Strongyloides
• These are all diseases of animal parasites in the wrong host, and the severity comes precisely from the larva being unable to complete its cycle — it wanders instead of settling, and the wandering is the disease