Cutaneous larva migrans is most commonly caused by which organism?

Explanation

## Correct Answer: B. Ancylostoma braziliense Cutaneous larva migrans (CLM) is a self-limited dermatological condition caused by percutaneous penetration of nematode larvae, most commonly **Ancylostoma braziliense**. This hookworm species is endemic in tropical and subtropical regions, particularly in sandy beaches and soil of Central and South America, Africa, and parts of Asia including India. The larvae of *A. braziliense* are uniquely adapted to penetrate human skin but cannot complete their life cycle in humans—they migrate through the dermis creating characteristic serpiginous (snake-like) tracks visible on the skin. The condition typically presents 1–2 weeks after exposure with intensely pruritic, raised, erythematous linear or curved tracks, often on the feet, buttocks, or lower extremities. Unlike other hookworms that can cause systemic disease (anemia, malnutrition), *A. braziliense* remains confined to the skin because the larvae cannot penetrate beyond the dermis to reach the lungs and intestines. The diagnosis is clinical, and treatment with topical or systemic anthelmintics (albendazole, ivermectin) is effective. In India, CLM is occasionally seen in travelers returning from endemic beaches or in coastal populations with poor sanitation. The key discriminator is that *A. braziliense* is the **only hookworm species that causes CLM as its primary manifestation**. ## Why the other options are wrong **A. Toxocara canis** — This causes **visceral larva migrans (VLM)**, not cutaneous larva migrans. *Toxocara* larvae migrate systemically through the lungs, liver, and other organs, causing fever, hepatomegaly, and eosinophilia. While *Toxocara* can rarely cause ocular larva migrans, it does not produce the characteristic serpiginous skin tracks of CLM. This is a common trap because both are larval migration syndromes. **C. Strongyloides stercolaris** — This causes **larva currens** (literally 'running larva'), a variant of cutaneous manifestation, but it is NOT the classic CLM. *Strongyloides* larvae migrate more rapidly and create urticarial tracks rather than the slow, serpiginous burrows of *A. braziliense*. Additionally, *Strongyloides* can cause systemic autoinfection and hyperinfection syndrome, making it pathophysiologically distinct from CLM. **D. Necator americanus** — This is a major human hookworm causing iron-deficiency anemia and protein malnutrition in endemic areas, but it does **not cause CLM**. *Necator* larvae penetrate skin and migrate to the lungs and intestines to establish infection; they do not remain in the dermis creating tracks. The larvae are adapted for human infection and complete their life cycle, unlike *A. braziliense*. ## High-Yield Facts - **Ancylostoma braziliense** is the most common cause of cutaneous larva migrans (CLM) worldwide, especially in tropical beaches. - CLM presents as **serpiginous, intensely pruritic tracks** in the dermis, typically on feet and buttocks, appearing 1–2 weeks after exposure. - **A. braziliense larvae cannot penetrate beyond the dermis** in humans, so CLM remains localized and self-limited (unlike systemic hookworm disease). - **Larva currens** (caused by *Strongyloides*) is faster-moving and urticarial, distinguishing it from the slow, linear burrows of CLM. - **Visceral larva migrans** (*Toxocara*) causes systemic organ involvement (hepatomegaly, fever, eosinophilia), not skin tracks. - Treatment: **albendazole 400 mg daily for 3–7 days** or **ivermectin 200 µg/kg** is effective; topical thiabendazole is an alternative. ## Mnemonics **CLM = Creeping Larva Migrans (A. braziliense)** **C**utaneous **L**arva **M**igrans = **A**ncylostoma **braziliense** (the only hookworm that stays in skin). Remember: *A. braziliense* = **A**borted in skin (cannot complete life cycle in humans). **Hookworm Skin Syndromes** **A. braziliense** → CLM (serpiginous tracks); **Strongyloides** → Larva currens (urticarial, fast); **Toxocara** → VLM (visceral organs). Use: When differentiating larval migration syndromes. ## NBE Trap NBE often pairs CLM with *Toxocara* (visceral larva migrans) because both are larval migration syndromes. The trap is confusing systemic organ involvement (VLM) with localized dermal tracks (CLM). The key discriminator is that *A. braziliense* is the **only species that causes CLM as its primary manifestation**. ## Clinical Pearl In India, CLM is occasionally seen in travelers returning from Goa, Kerala, or other coastal beaches, or in children playing in contaminated sandy soil near beaches. The intense pruritus often leads to secondary bacterial infection if scratched. Bedside diagnosis is clinical; no need for serology or biopsy. Reassure patients that CLM is self-limited and will resolve spontaneously in 4–6 weeks even without treatment, though anthelmintics accelerate healing. _Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 46 (Nematodes); Harrison's Principles of Internal Medicine Ch. 219 (Helminthic Infections)_