Cutaneous Larva Migrans

Pathogenesis and How the Larvae Invade

Causative Organisms and Life Cycle

• Main causes: Larvae of the dog and cat hookworm Ancylostoma braziliense (the most common cause) and the dog hookworm Ancylostoma caninum. Less common species include Uncinaria stenocephala and Bunostomum phlebotomum.
• How infection happens:
  • Hookworm eggs are passed in dog or cat feces into warm, moist soil or sand (beaches, gardens, construction sites).
  • The eggs hatch into rhabditiform larvae, which then develop into infective filariform (L3) larvae that can live freely in damp soil for several weeks.
  • When bare skin touches contaminated soil or sand, the L3 larvae release hyaluronidase and metalloproteases that break down the extracellular matrix, allowing them to slip into the epidermis or through hair follicles.

Anatomic Confinement and the Immune Response in the Skin

• The anatomic "trap": Unlike human hookworms (Ancylostoma duodenale or Necator americanus), animal hookworm larvae lack the receptors and enzymes needed to cross the basement membrane into dermal veins. They therefore stay confined to the spinous layer (stratum spinosum) and basal layer of the epidermis.
• Speed and direction of movement: The larvae crawl sideways at 2 mm to 2 cm a day, leaving behind a tunnel packed with inflammatory cells.
• Host immune response: Excretory/secretory (E/S) antigens from the larvae trigger delayed (type IV) and type I hypersensitivity in the skin. T helper 2 (Th2) cells release IL-4 and IL-5, drawing eosinophils to surround the tunnel. These release histamine and major basic protein (MBP), causing maddening itch and red, swollen edges.

Clinical Features

Classic Creeping Eruption:

• Onset: 1–5 days after exposure, a slightly itchy, pinhead-sized red papule appears at the entry site.
• Progression: Over a few days, the papule extends into a winding (serpiginous) or linear track, raised above the skin, bright pink or deep red, and 2–4 mm wide.
• Typical sites: The feet (between the toes, the top, and the sole), buttocks, thighs, hands, and back, which are the areas that touch damp sand or soil directly.
• Symptoms: Intense itching that worsens at night, causing sleeplessness and scratching that breaks the skin and leads to secondary bacterial infection (Staphylococcus aureus, Streptococcus pyogenes).

Hookworm Folliculitis Variant:

• Less common; occurs when many larvae enter the hair follicle openings at once (usually on the buttocks and thighs).
• Appearance: Dozens to hundreds of itchy, red-rimmed papules and pustules clustered around hair follicles, without obvious tracks. It is easily mistaken for staphylococcal or Malassezia folliculitis.

Vesicular / Bullous Variant (Bullous CLM): A very strong delayed hypersensitivity reaction to hookworm antigens produces tense, clear fluid-filled blisters along the path of the larva.

How We Diagnose CLM at Haute-Derma

Detailed History and Exposure Assessment: We ask about recent beach trips, lying or sitting on contaminated sand, gardening, walking barefoot, or contact with dogs or cats that are not regularly dewormed.

Advanced Dermoscopy (Dermoscopic Mapping):

• What we see: At the leading end of the tunnel, dermoscopy shows faint gray or light brown tubular structures (the body of the larva) alongside red congested bands and surrounding looped vessels.
• Finding the leading edge: The live larva usually sits 1–2 cm ahead of the end of the raised red track, in skin that looks normal but is where the larva is heading.

Supporting Blood and Laboratory Tests:

• Complete blood count (CBC): Eosinophils may be mildly to moderately raised (5–15%) when many larvae are present at once.
• Skin biopsy: Not recommended routinely, because the larva moves quickly and lies beyond the inflamed tunnel; the larva is found on histology in fewer than 20% of biopsies.

Treatment and Clinical Management at Haute-Derma

First-Line Systemic Antiparasitic Treatment

• Albendazole (preferred first choice):
  • Dose: 400 mg by mouth once daily for 3–5 consecutive days.
  • Clinical tip: Always take it right after a fatty meal (for example, whole milk, eggs, or cooking oil), which increases absorption into the bloodstream 4–5 times.
  • Clearance and cure rates are very high.
• Ivermectin (alternative option):
  • Dose: A single oral dose of 200 µg/kg on an empty stomach (2 hours before eating).
  • Extensive disease or multiple tracks: Repeat a second 200 µg/kg dose after 7 days.

Topical Treatment (for single lesions or young children)

• Albendazole 10% topical (or compounded thiabendazole 15% cream): Apply to the lesion and the surrounding normal skin within a 2 cm radius, 3 times a day for 10–14 days.

Treating Hypersensitivity Symptoms and Secondary Infection

• Itch relief: A second-generation H1 antihistamine (levocetirizine 5 mg or desloratadine 5 mg in the evening).
• Severe bullous inflammation: A short course (3–5 days) of a moderate- to high-potency topical corticosteroid (betamethasone dipropionate or clobetasol propionate) to reduce swelling and itch.
• Antibiotics for secondary infection: If scratching has led to pustules, yellow crusts, or painful swelling, add cephalexin 500 mg twice daily for 7 days.