Cutaneous larva migrans (creeping eruption) — Viva

Stem (read aloud to candidate)

A 30-year-old man returns from a 2-week beach holiday in the Caribbean. He presents to your dermatology clinic with a 5-day history of an intensely itchy, slowly advancing, serpiginous, erythematous tract on the sole of his right foot. He walked barefoot on the beach most days and sat on the sand. There are no systemic symptoms. Examine the lesion, list your differential diagnosis, and outline your management.

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Q1: Definition and clinical presentation (2 min)

What is cutaneous larva migrans, and how does it classically present?

Expected core points:

• Definition: intensely pruritic, serpiginous, creeping erythematous tract caused by the intraepidermal migration of animal hookworm larvae. Humans are an aberrant (dead-end) host because the larva cannot complete its natural life cycle.
• Incubation: typically a few days after skin contact with contaminated sand or soil.
• Hallmark: a slowly advancing (millimetres per day), raised, erythematous, serpiginous or linear tract on a contact site (feet, buttocks, abdomen, thighs).
• The leading edge is ahead of the visible inflammatory tract and may show a small vesicle.
• Usually 1–3 tracts; multiple tracts occur in a minority of patients.
• Pruritus is the dominant symptom and is often worse at night, sometimes preventing sleep.

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Bonus: identify CLM as among the most common dermatoses in returned travellers (13% of travel-acquired skin diagnoses in CanTravNet surveillance).^[7]

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Q2: Differential diagnosis (3 min)

Which conditions would you consider in the differential, and how would you distinguish them?

Expected core points (at least three):

• Larva currens (Strongyloides stercoralis) — rapid migration (centimetres per HOUR), recurrent in the same site, often perianal/buttock, with eosinophilia and abdominal symptoms. Strongyloides serology and stool O&P. Requires systemic ivermectin.
• Cutaneous gnathostomiasis (Gnathostoma spinigerum) — migratory subcutaneous swellings (not a thin tract), marked eosinophilia, history of raw freshwater fish in Asia or Mexico. Gnathostoma serology; albendazole per the local protocol if confirmed.
• Cutaneous myiasis (Dermatobia hominis, Cordylobia anthropophaga) — visible maggot in the centre of a furuncular lesion. Extract with forceps after occlusion.
• Tinea corporis — annular scaly plaque with central clearing; KOH positive for hyphae.
• Erythema chronicum migrans (Lyme disease) — large expanding annular erythema around a tick bite; doxycycline.
• Scabies — short burrows in webs of fingers and wrists; multiple contacts; microscopy for mites.

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Bonus: name the migration rate as the single most useful distinguishing bedside feature: larva currens migrates centimetres per hour (far faster than the slow CLM tract); gnathostomiasis causes intermittent swellings.^[5]

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Q3: Investigations (2 min)

What investigations would you arrange, and is a biopsy helpful?

Expected core points:

• Diagnosis is clinical — travel history plus the characteristic creeping serpiginous tract on a contact site. No routine laboratory test is required to start treatment.
• Biopsy is rarely helpful — the larva sits ahead of the visible tract and is rarely captured on biopsy. Histology, when performed, shows an epidermal tract with spongiosis, intraepidermal vesiculation, and a mixed inflammatory infiltrate with eosinophils; larval cross-sections are uncommon.
• Full blood count — peripheral eosinophilia is uncommon in simple CLM; significant eosinophilia should prompt investigation for other helminths (Strongyloides serology, stool O&P × 3, Toxocara serology, schistosomiasis serology if exposure fits).
• Strongyloides serology and stool O&P if the tract is unusually rapid, recurrent, or perianal — to exclude larva currens.
• Gnathostoma serology if migratory subcutaneous swellings, marked eosinophilia, and raw-fish exposure.
• Dermoscopy (if available) can occasionally help locate the larva at the leading edge.

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Q4: Management (3 min)

Outline your stepwise approach to management.

Expected core points:

• First-line: oral ivermectin as a SINGLE dose — drug of choice (100% cure vs 46% for single-dose albendazole in the randomised comparison).^[1] See the local protocol for the exact dose; avoid in pregnancy, in small children, and with possible Loa loa co-infection (encephalopathy risk).
• Second-line: oral albendazole over several days — use when ivermectin is contraindicated, unavailable, or in patients with Loa loa co-infection (relapse after single-dose albendazole was common — about half the randomised patients).^[1] See the local protocol for dose and duration; caution in first-trimester pregnancy.
• Symptomatic: oral antihistamines (cetirizine 10 mg, loratadine 10 mg, hydroxyzine 25 mg at night) for pruritus. Topical corticosteroid (mild-to-moderate potency) for short-term relief of intense inflammation, but not over infected skin.
• Treat secondary bacterial infection if impetiginised or cellulitic: oral flucloxacillin (or erythromycin/clarithromycin if penicillin-allergic); check tetanus immunisation.
• Topical thiabendazole is historic, occasionally useful for very localised lesions when oral therapy is contraindicated.
• Cryotherapy of the leading edge is unreliable — the larva sits ahead of the visible tract, and the procedure often blisters normal skin without eradicating the parasite. Not recommended.
• Repeat the dose after 1–2 weeks if the tract has not stopped advancing or new tracts appear (a minority of patients).

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Q5: Complications and prognosis (2 min)

What are the main complications, and what is the typical prognosis?

Expected core points:

• Secondary bacterial infection is the most common complication: impetiginisation, folliculitis, cellulitis, erysipelas; rarely abscess or lymphangitis.
• Diagnostic delay and misdiagnosis (often weeks in primary care) — commonly mistaken for scabies, tinea, Lyme disease, or contact dermatitis; inappropriate topical steroids or antifungals allow the larva to continue migrating.
• Treatment failure with single-dose ivermectin (a minority) — second dose, switch to albendazole, or reconsider the diagnosis (larva currens, gnathostomiasis, myiasis).
• Löffler-like pulmonary eosinophilia in patients with concomitant helminth infection (Ascaris, Strongyloides), not CLM itself.
• Marked peripheral eosinophilia should prompt investigation for other helminths (Strongyloides, Toxocara, filaria, schistosomiasis).
• Prognosis is excellent with appropriate treatment: cure with ivermectin, symptomatic improvement within days, complete resolution within weeks; spontaneous resolution over weeks without treatment.
• No long-term sequelae unless secondary infection causes scarring; recurrence reflects re-exposure rather than treatment failure.

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Bonus questions (if time permits)

Q6: How would you adapt your management in pregnancy?

• Ivermectin is generally avoided in pregnancy (insufficient safety data).
• Albendazole is conventionally avoided in the first trimester (animal teratogenicity); the threshold for treatment in pregnancy is lower because the pruritus itself affects wellbeing.
• Topical thiabendazole is a useful alternative because systemic absorption is minimal.
• Decision should be individualised with obstetric and infectious-disease input.

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Q7: What public-health advice would you give this patient?

• Avoid barefoot walking on tropical beaches; wear sandals or water shoes.
• Use beach mats or towels when sitting or lying on sand.
• Deworm domestic pets; keep dogs and cats off beaches and children's sandboxes.
• Treat contaminated soil under raised houses (occupational CLM).

Q8: A traveller returns from West Africa with CLM and a possible Loa loa exposure. What would you do?

• Screen for Loa loa microfilaraemia with a daytime peripheral blood film before giving ivermectin.
• Ivermectin can precipitate encephalopathy in patients with high Loa loa microfilaraemia (>30,000 microfilariae/mL).
• If microfilaraemia is detected, consider albendazole (which does not kill Loa loa microfilariae rapidly) and refer to a tropical-disease specialist.
• Treat the CLM with albendazole as first-line in this scenario, per the local protocol for dose and duration.^[1]

References4ShowHide

1. [1]Caumes E, et al. A randomized trial of ivermectin versus albendazole for the treatment of cutaneous larva migrans Am J Trop Med Hyg, 1993.PMID 8250105
2. [4]Heukelbach J, et al. Epidemiological and clinical characteristics of hookworm-related cutaneous larva migrans Lancet Infect Dis, 2008.PMID 18471775
3. [5]Tian Y, et al. Larva Currens: Report of Seven Cases and Literature Review Am J Trop Med Hyg, 2023.PMID 36535252
4. [7]Stevens MS, et al. Dermatoses among returned Canadian travellers and immigrants: surveillance report based on CanTravNet data, 2009-2012 CMAJ Open, 2015.PMID 25844364