Question
Cutaneous larva migrans
Answer
Cutaneous larva migrans (CLM), colloquially known as “creeping eruption,” is a self-limiting parasitic skin infestation caused by the migration of animal hookworm larvae through the human epidermis — most commonly Ancylostoma braziliense (the dog/cat hookworm) — humans being an accidental, dead-end host in whom the larvae cannot complete their normal life cycle (unlike in the natural dog/cat host, where they would penetrate to reach the intestine and mature into adult worms).
Transmission: larvae hatch from eggs passed in dog/cat faeces onto soil/sand (classically warm, moist, sandy environments — beaches, playgrounds contaminated by animal faeces); infective third-stage filariform larvae in the soil penetrate exposed human skin (typically bare feet or other skin in direct soil/sand contact).
Clinical features: since humans are an aberrant/dead-end host, the larvae lack the enzymes needed to penetrate the dermis and enter the bloodstream (as they would in the natural host), and instead remain confined to the epidermis, migrating slowly (a few millimetres to centimetres per day) — producing a characteristic serpiginous (snake-like), intensely pruritic, raised, erythematous, thread-like track on the skin that advances visibly over days, most commonly on the feet, buttocks, or other areas of skin exposed to contaminated soil/sand.
Natural course: since the larvae cannot complete their life cycle in the aberrant human host, the infestation is ultimately self-limiting, with larvae dying and the lesion resolving spontaneously over weeks to a few months even without treatment, though the intense itching prompts most patients to seek treatment for symptomatic relief and to shorten the disease course.
Diagnosis: primarily clinical, based on the highly characteristic serpiginous, migrating track and a relevant history of exposure to contaminated soil/sand (e.g., a tropical beach holiday); biopsy is rarely needed and often fails to demonstrate the larva, since it is typically located slightly ahead of the visible track.
Treatment: oral albendazole or ivermectin (systemic therapy is generally preferred over topical therapy for reliable cure); topical thiabendazole is an alternative for localized lesions.
Prevention: avoiding walking barefoot on potentially contaminated soil/sand (particularly beaches frequented by stray dogs/cats), and deworming of pet animals.