Cutaneous Larva Migrans (CLM)
Published on September 19, 2026
Risk Factors
Recent travel to tropical or subtropical regions; walking barefoot on sandy beaches or soil; children playing in sandboxes; contact with soil contaminated by dog or cat feces; occupational exposure (plumbers, gardeners, farmers, construction workers in endemic areas)
Etiology
Larvae of animal hookworms, most commonly Ancylostoma braziliense (from dogs and cats). Other species include A. caninum, A. ceylanicum, and Uncinaria stenocephala. Humans are accidental dead-end hosts.
Presentation
Intensely pruritic, slowly migrating, raised, erythematous serpiginous (snake-like) track on the skin, most commonly on the feet, buttocks, or hands. Track advances approximately 1 to 2 cm per day.
Classic Exam
Elevated, erythematous, serpiginous or linear track with an advancing border; surrounding skin may show vesicles, excoriations from scratching, or signs of secondary bacterial infection
Diagnostics
Clinical diagnosis. No biopsy or serology required. Peripheral eosinophilia may be present but is not diagnostic. Dermoscopy may reveal the larval body at the leading edge.
Management
Ivermectin 200 mcg/kg orally as a single dose (preferred) OR Albendazole 400 mg orally daily for 3 days. Topical thiabendazole for very limited disease. Antihistamines for symptom relief.
Keywords
"Serpiginous track," "creeping eruption," "barefoot on the beach," "sandy soil," "pruritic migrating track," "tropical travel," "dead-end host"
01Pathophysiology
Cutaneous larva migrans (CLM) begins when filariform (infective, third-stage) larvae of animal hookworms are deposited into warm, moist, sandy soil through the feces of infected dogs or cats. The larvae can survive in the environment for weeks under favorable conditions.
When a human walks barefoot or lies on contaminated ground, the larvae actively penetrate intact skin using proteolytic enzymes. The key concept here is that humans are accidental, dead-end hosts. Unlike in the definitive animal host, the larvae in humans cannot penetrate the epidermal basement membrane to reach the dermis, enter the bloodstream, and complete their normal life cycle through the lungs and gut. They are effectively trapped within the epidermis.
Because the larvae are confined to the superficial layers of skin, they migrate laterally through the epidermis at a rate of about 1 to 2 cm per day, leaving behind a trail of mechanical tissue destruction and an inflammatory response. This migration is what creates the characteristic serpiginous (snake-like), raised, erythematous track visible on examination. The intense pruritus is driven by a localized type I and type IV hypersensitivity reaction to larval secretions and excretory products.
An important point for exam questions is that the larva is always located a few centimeters ahead of the visible track. The track you see represents the inflammatory reaction trailing behind the larva, not the larva's current position. This fact is why biopsy of the track itself almost never captures the organism and why cryotherapy applied to the visible end of the track is ineffective.
The disease is self-limited. Because the larvae cannot complete their life cycle in humans, they will eventually die within weeks to months even without treatment. However, treatment is strongly recommended to shorten the duration, relieve pruritus, and prevent secondary bacterial infection from excoriation.
02Classification and Clinical Manifestation
Classic serpiginous track
Location
Feet (most common), buttocks, hands, knees
Description
Raised, erythematous, pruritic, snake-like linear track that advances daily. The hallmark presentation.
Hookworm folliculitis
Location
Buttocks, trunk
Description
Papulovesicular or pustular eruption centered on hair follicles. Occurs when larvae invade follicular structures. Often confused with bacterial folliculitis or scabies.
Vesiculobullous form
Location
Any site of penetration
Description
Vesicles or bullae form along or near the track, reflecting a more vigorous inflammatory response. Can be mistaken for allergic contact dermatitis.
Secondary impetiginization
Location
Over excoriated tracks
Description
Superimposed bacterial infection (usually Staphylococcus aureus or Streptococcus pyogenes) due to scratching. Presents with crusting, erythema, warmth, and purulent discharge.
Form | Location | Description |
|---|---|---|
Classic serpiginous track | Feet (most common), buttocks, hands, knees | Raised, erythematous, pruritic, snake-like linear track that advances daily. The hallmark presentation. |
Hookworm folliculitis | Buttocks, trunk | Papulovesicular or pustular eruption centered on hair follicles. Occurs when larvae invade follicular structures. Often confused with bacterial folliculitis or scabies. |
Vesiculobullous form | Any site of penetration | Vesicles or bullae form along or near the track, reflecting a more vigorous inflammatory response. Can be mistaken for allergic contact dermatitis. |
Secondary impetiginization | Over excoriated tracks | Superimposed bacterial infection (usually Staphylococcus aureus or Streptococcus pyogenes) due to scratching. Presents with crusting, erythema, warmth, and purulent discharge. |
The distribution of lesions depends on the area of skin that was in contact with contaminated soil. The feet and interdigital spaces are the most common site because of barefoot walking. The buttocks are involved in people who sat or lay on the beach. Hand involvement occurs in children who play in sandboxes.
03Diagnostic Workup
Clinical examination
Role
Best initial test AND gold standard
Expected Finding
Characteristic serpiginous, erythematous, pruritic track in a patient with appropriate exposure history
Dermoscopy
Role
Supportive (not required)
Expected Finding
May reveal a translucent, brownish larval body at the leading edge of the track
CBC with differential
Role
Supportive (not required)
Expected Finding
Peripheral eosinophilia may be present, but is neither sensitive nor needed for diagnosis
Skin biopsy
Role
Not recommended
Expected Finding
Typically shows nondiagnostic eosinophilic infiltrate; larvae are almost never captured because they reside ahead of the visible track
Serology / Stool studies
Role
Not indicated
Expected Finding
These are not useful because the larvae do not complete their life cycle in humans; there is no systemic infection and no gut involvement
Test | Role | Expected Finding |
|---|---|---|
Clinical examination | Best initial test AND gold standard | Characteristic serpiginous, erythematous, pruritic track in a patient with appropriate exposure history |
Dermoscopy | Supportive (not required) | May reveal a translucent, brownish larval body at the leading edge of the track |
CBC with differential | Supportive (not required) | Peripheral eosinophilia may be present, but is neither sensitive nor needed for diagnosis |
Skin biopsy | Not recommended | Typically shows nondiagnostic eosinophilic infiltrate; larvae are almost never captured because they reside ahead of the visible track |
Serology / Stool studies | Not indicated | These are not useful because the larvae do not complete their life cycle in humans; there is no systemic infection and no gut involvement |
CLM is one of the few diagnoses where the clinical picture alone is both the best initial test and the most accurate test. A vignette describing a patient who recently returned from a tropical beach vacation and presents with an intensely pruritic, slowly advancing serpiginous track on the foot is essentially pathognomonic.
Do not order a biopsy. This is a common trap. A biopsy will show a perivascular eosinophilic infiltrate and possibly a tunnel in the epidermis, but the larva is virtually never found in the specimen because it has already migrated beyond the biopsy site. Ordering a biopsy wastes time and does not change management.
Stool ova and parasite exams are irrelevant here. Unlike Strongyloides stercoralis or Necator americanus (human hookworms), the animal hookworm larvae in CLM never reach the gastrointestinal tract in humans. If you see stool studies offered as an answer choice, it is a distractor.
04Management and Treatment
First-line (oral)
Agent
Ivermectin
Dose and Regimen
200 mcg/kg orally, single dose
Notes
Preferred for its efficacy and convenience. Cure rates exceed 95%.
Alternative (oral)
Agent
Albendazole
Dose and Regimen
400 mg orally once daily for 3 days
Notes
Used when ivermectin is unavailable. Single-dose albendazole has lower cure rates, so 3-day course is recommended.
Topical (localized disease)
Agent
Thiabendazole 10 to 15% cream/ointment
Dose and Regimen
Applied topically 2 to 3 times daily for 5 to 7 days over the track and 2 cm beyond the leading edge
Notes
Reserved for very limited or single-track disease. Less reliable than systemic therapy.
Symptomatic
Agent
Antihistamines (e.g., cetirizine, diphenhydramine)
Dose and Regimen
Standard doses
Notes
For pruritus relief. Do not address the underlying infection.
Secondary infection
Agent
Oral antibiotics (e.g., cephalexin, dicloxacillin)
Dose and Regimen
Standard doses for skin infection
Notes
Only if secondary bacterial infection has developed from excoriation.
Setting | Agent | Dose and Regimen | Notes |
|---|---|---|---|
First-line (oral) | Ivermectin | 200 mcg/kg orally, single dose | Preferred for its efficacy and convenience. Cure rates exceed 95%. |
Alternative (oral) | Albendazole | 400 mg orally once daily for 3 days | Used when ivermectin is unavailable. Single-dose albendazole has lower cure rates, so 3-day course is recommended. |
Topical (localized disease) | Thiabendazole 10 to 15% cream/ointment | Applied topically 2 to 3 times daily for 5 to 7 days over the track and 2 cm beyond the leading edge | Reserved for very limited or single-track disease. Less reliable than systemic therapy. |
Symptomatic | Antihistamines (e.g., cetirizine, diphenhydramine) | Standard doses | For pruritus relief. Do not address the underlying infection. |
Secondary infection | Oral antibiotics (e.g., cephalexin, dicloxacillin) | Standard doses for skin infection | Only if secondary bacterial infection has developed from excoriation. |
The next best step for a patient presenting with a classic serpiginous track and relevant travel history is to initiate treatment with oral ivermectin at 200 mcg/kg as a single dose. This is the preferred first-line agent due to its high efficacy, simple dosing, and excellent tolerability. No diagnostic workup needs to precede treatment.
If ivermectin is not available, albendazole at 400 mg daily for 3 days is the alternative. Note that a single dose of albendazole (sometimes offered as an answer choice) has significantly lower cure rates compared to the 3-day course. If an exam vignette asks about "most appropriate treatment" and offers both single-dose albendazole and 3-day albendazole, always choose the 3-day regimen.
For very localized disease with a single short track, topical thiabendazole can be considered, but systemic therapy is preferred in most clinical scenarios because the larva may have migrated beyond the visible track.
Contraindications and cautions:
Ivermectin should be avoided in pregnant women and in children weighing less than 15 kg due to insufficient safety data. In these populations, albendazole is the preferred alternative, although albendazole is also Category C in pregnancy and should be used only when the benefit outweighs the risk (generally deferred until after the first trimester if possible).
Cryotherapy is not recommended. It is ineffective because the larva is located ahead of the visible track, and applying liquid nitrogen to the end of the track causes painful tissue destruction without killing the organism. If cryotherapy appears as a treatment option on a question, it is a distractor.
The disease will self-resolve within 2 to 8 weeks without treatment because the larva dies in a dead-end host, but treatment is always recommended to relieve symptoms and prevent complications.
05Differential Diagnosis and Distractors
Larva currens (Strongyloides stercoralis)
Why It Is Similar
Also presents as a migrating, pruritic, linear skin eruption caused by a helminth larva
Key Discriminator
Larva currens moves much faster (5 to 10 cm per hour vs. 1 to 2 cm per day), is typically perianal or truncal (not on feet), and carries risk of disseminated hyperinfection in immunosuppressed patients. Look for autoinfection cycle and systemic symptoms.
Allergic contact dermatitis (e.g., phytophotodermatitis)
Why It Is Similar
Can produce linear, erythematous, pruritic lesions after outdoor exposure
Key Discriminator
Contact dermatitis is static and does not migrate. The history will point to plant or chemical exposure rather than sandy soil. No advancing track.
Tinea corporis
Why It Is Similar
Ring-shaped or serpiginous erythematous lesion, pruritic
Key Discriminator
Tinea is annular with central clearing, not a linear migrating track. KOH preparation is positive for fungal hyphae. No travel history required.
Scabies
Why It Is Similar
Intensely pruritic skin lesions with burrows
Key Discriminator
Scabies burrows are short (a few millimeters), favor interdigital web spaces and wrists, and are associated with nocturnal pruritus. Mineral oil prep shows mites, eggs, or scybala.
Myiasis (fly larva)
Why It Is Similar
Parasitic larva in the skin after tropical travel
Key Discriminator
Myiasis typically presents as a furuncle-like nodule (boil) with a central pore, not a serpiginous track. The larva is stationary within the nodule.
Loiasis (Loa loa)
Why It Is Similar
Migrating subcutaneous swellings after travel to endemic areas (West/Central Africa)
Key Discriminator
Loa loa causes Calabar swellings (transient, deep subcutaneous edema), not superficial serpiginous tracks. Adult worm may be seen migrating across the conjunctiva. Blood smear shows microfilariae with diurnal periodicity.
Differential | Why It Is Similar | Key Discriminator |
|---|---|---|
Larva currens (Strongyloides stercoralis) | Also presents as a migrating, pruritic, linear skin eruption caused by a helminth larva | Larva currens moves much faster (5 to 10 cm per hour vs. 1 to 2 cm per day), is typically perianal or truncal (not on feet), and carries risk of disseminated hyperinfection in immunosuppressed patients. Look for autoinfection cycle and systemic symptoms. |
Allergic contact dermatitis (e.g., phytophotodermatitis) | Can produce linear, erythematous, pruritic lesions after outdoor exposure | Contact dermatitis is static and does not migrate. The history will point to plant or chemical exposure rather than sandy soil. No advancing track. |
Tinea corporis | Ring-shaped or serpiginous erythematous lesion, pruritic | Tinea is annular with central clearing, not a linear migrating track. KOH preparation is positive for fungal hyphae. No travel history required. |
Scabies | Intensely pruritic skin lesions with burrows | Scabies burrows are short (a few millimeters), favor interdigital web spaces and wrists, and are associated with nocturnal pruritus. Mineral oil prep shows mites, eggs, or scybala. |
Myiasis (fly larva) | Parasitic larva in the skin after tropical travel | Myiasis typically presents as a furuncle-like nodule (boil) with a central pore, not a serpiginous track. The larva is stationary within the nodule. |
Loiasis (Loa loa) | Migrating subcutaneous swellings after travel to endemic areas (West/Central Africa) | Loa loa causes Calabar swellings (transient, deep subcutaneous edema), not superficial serpiginous tracks. Adult worm may be seen migrating across the conjunctiva. Blood smear shows microfilariae with diurnal periodicity. |
06Traps and High-Yield Pearls
The most common way students get questions on CLM wrong involves two pitfalls. First, they order unnecessary workup. When a vignette describes a textbook serpiginous track in a returning tropical traveler, the correct answer is to treat empirically with ivermectin, not to order a biopsy, stool studies, or serology. CLM is a clinical diagnosis. Any answer choice suggesting a biopsy is designed to trap students who default to tissue confirmation for every dermatologic condition.
Second, students frequently confuse CLM with larva currens caused by Strongyloides stercoralis. The discriminating feature is the speed and location of migration. CLM moves slowly (1 to 2 cm per day) and favors the feet. Larva currens races across the skin (up to 10 cm per hour), is perianal or truncal, and is clinically significant because Strongyloides can cause fatal disseminated hyperinfection in immunocompromised patients, particularly those on corticosteroids.
Another common trap is selecting cryotherapy as treatment. Cryotherapy is ineffective and harmful, and it appears as a distractor designed to catch students who do not understand that the larva is ahead of the visible track.
The core competency being tested is pattern recognition of a classic dermatologic presentation in the context of travel medicine, combined with the ability to avoid over-investigation and select appropriate antiparasitic therapy. If you see "serpiginous," "creeping," "barefoot," and "beach" in the same stem, the answer is cutaneous larva migrans, and the treatment is ivermectin.