Ectoparasitic Infestations

Scabies - Itchy Mite Mayhem

• Agent: Sarcoptes scabiei var. hominis. Lifecycle: Mite burrows, lays eggs, mature in ~2 wks.
• Transmission: Prolonged skin-to-skin contact; fomites (esp. crusted scabies).
• Clinical Features:
  • ⭐ Hallmark: Intense nocturnal pruritus.
  • Burrows: Serpiginous lines. 📌 Key Sites: Finger webs, wrists, axillae, elbows, genitals, beltline, areolae.
  • Lesions: Papules, vesicles; nodules (genitals, axillae).
  • Special Forms:
    • Crusted (Norwegian): Immunocompromised; hyperkeratotic, highly contagious, minimal itch.
    • Infants: Face, scalp, palms, soles often involved.
• Diagnosis:
  • Clinical (nocturnal itch, contacts).
  • Microscopy (skin scraping): Mites, eggs, scybala.
  • Burrow Ink Test.
• Treatment:
  • DOC: Permethrin 5% cream (neck-down, 8-14h, repeat 1 wk).
  • Oral Ivermectin (200 mcg/kg, repeat 1-2 wks): For crusted, widespread, outbreaks.
  • Alternatives: Benzyl benzoate (10-25%), Crotamiton (10%). ⚠️ Lindane (1%) - neurotoxic.
  • Management: Treat contacts. Hot wash/seal fomites (72h). Pruritus may persist 2-4 wks.

⭐ Nocturnal pruritus is a hallmark symptom of scabies. Awaiting image generation for "Scabies burrows on interdigital skin or Sarcoptes scabiei mite microscopy"...

Pediculosis - Lousy Lice Lowdown

Parasitic infestations caused by lice. Three types:

• Pediculus humanus capitis (head louse)
• Pediculus humanus corporis (body louse)
• Pthirus pubis (crab louse, pubic louse)

Transmission: Primarily direct contact; fomites (e.g., hats, bedding, clothing).

1. Pediculosis Capitis (Head Lice)

• Clinical: Intense pruritus (esp. occiput, post-auricular), visible nits (eggs cemented to hair shafts), adult lice, excoriations, secondary bacterial infection (impetigo).
• Diagnosis: Visualization of live lice or viable nits (<1 cm from scalp).
• Treatment: Topical pediculicides (Permethrin 1% lotion - first line; Malathion 0.5%; Ivermectin lotion). Oral Ivermectin for resistant cases. Wet combing. Retreat in 7-10 days.

2. Pediculosis Corporis (Body Lice)

• Clinical: Associated with poor hygiene/homelessness. Lice live and lay eggs in seams of clothing, visit body to feed. Pruritus, linear excoriations (shoulders, trunk), post-inflammatory hyperpigmentation.
• Complications: Vector for Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (louse-borne relapsing fever), Bartonella quintana (trench fever).
• Treatment: Improve personal hygiene, frequent change and laundering of clothing/bedding at high temperatures (>55°C), iron seams. Pediculicide application to body usually not needed if hygiene measures are thorough.

⭐ Body lice (Pediculosis corporis) are significant vectors for diseases like epidemic typhus, trench fever, and relapsing fever.

3. Pediculosis Pubis (Pthiriasis/Crab Lice)

• Clinical: Intense pruritus in pubic and anogenital areas. Nits and adult lice at base of pubic hairs. Maculae ceruleae (sky-blue or slate-grey macules, 0.5-1 cm, at feeding sites).
• Sites: Pubic hair, axillary hair, chest hair, beards, eyebrows, eyelashes (pediculosis ciliaris).
• Transmission: Usually sexual contact.
• Treatment: Topical Permethrin 1% cream rinse or pyrethrins with piperonyl butoxide. Malathion 0.5% lotion. Treat sexual partners. For eyelashes: ophthalmic-grade petrolatum ointment BID for 8-10 days; mechanical removal. Consider STI screening.

Other Infestations - Creepy Crawler Cameos

• Myiasis: Tissue infestation by fly larvae (maggots).

  • Types: Furuncular (boil-like, common), wound, cavitary.
  • Causative Flies: E.g., Dermatobia hominis (human botfly), Cordylobia anthropophaga (tumbu fly).
  • Clinical: Painful, itchy, erythematous nodule with a central pore (punctum); sensation of movement.
  • Management: Occlusion (e.g., petroleum jelly) to induce hypoxia, then gentle surgical extraction of larva.

• Tungiasis (Sand Flea Disease): Infestation by burrowing female sand flea Tunga penetrans.

  • Clinical: Intensely itchy, painful papule/nodule, often on feet (periungual), evolves to whitish patch with a central black dot (flea's abdomen/eggs).

    ⭐ In tungiasis, the female flea burrows head-first into the skin, often leaving its posterior end visible as a black dot.

  • Complications: Severe inflammation, pain, secondary bacterial infections, ulceration, auto-amputation of digits.
  • Treatment: Sterile surgical extraction of intact flea, wound care, tetanus prophylaxis (if indicated).

High‑Yield Points - ⚡ Biggest Takeaways

• Scabies: Sarcoptes scabiei; intense nocturnal pruritus, burrows. DOC: Permethrin 5%. Ivermectin for crusted/severe.
• Pediculosis Capitis: P. humanus capitis; scalp itch, nits on hair. Treat: Permethrin 1%.
• Pediculosis Corporis: P. humanus corporis; poor hygiene, lice in clothing, disease vector.
• Pediculosis Pubis: Phthirus pubis; pubic itch, STI, maculae ceruleae.
• Diagnosis: Clinical; microscopy confirms mites, lice, or nits.
• Management: Treat close contacts simultaneously; fomite disinfection (hot wash).