255.1 🎓 醫孞生版

255.1.0.1 📌 䞀頁重點

255.1.0.1.1 Scabies (Sarcoptes scabiei)
255.1.0.1.1.1 Background
  • Microscopic mite; female burrows into skin to lay eggs
  • Highly contagious
  • Worldwide; outbreaks in:
    • Long-term care facilities
    • Daycare
    • Crowded housing
    • Homeless populations
    • Households
255.1.0.1.1.2 Transmission
  • Skin-to-skin contact (prolonged ≥ 10-15 min typically)
  • Fomites less common
  • Sexual contact often
  • Person-to-person primary
255.1.0.1.1.3 Clinical
  • Severe pruritus (especially at night)
  • Most affected: finger webs, wrists, axillae, areola, umbilicus, genitalia (penis, scrotum, vulva), buttocks, ankles
  • Burrows (linear, 1-15 mm, gray-thread-like) — pathognomonic
  • Papules, vesicles
  • Pruritus often disproportional to lesions
255.1.0.1.1.4 Norwegian / Crusted Scabies
  • Massive infestation (millions of mites)
  • Immunocompromise (HIV/AIDS, transplant, elderly, intellectual disability)
  • Thick crusted plaques + scaling
  • Often less itchy
  • Highly infectious
  • ICU outbreaks documented
255.1.0.1.1.5 Diagnosis
  • Clinical (history + classic distribution + burrows)
  • Microscopy of scraping (mineral oil) — mite, eggs, fecal pellets
  • Dermoscopy (“hang-glider sign” — mite head)
  • PCR of scraping (emerging)
255.1.0.1.1.6 Treatment
  • Permethrin 5% cream (topical) — first-line; apply neck-to-toes overnight; repeat in 1 week
  • Ivermectin 200 µg/kg PO × 2 doses 1-2 weeks apart — preferred for crusted scabies + epidemics
  • Treat all household + close contacts simultaneously
  • Wash clothing + bedding hot water or seal in plastic bag 72 hr (mites die without skin)
  • Itching may persist weeks after treatment (post-treatment pruritus from dead mites + dermatitis)
  • Norwegian scabies: combined ivermectin + topical permethrin + keratolytic; multiple cycles
255.1.0.1.1.7 Other Treatments
  • Crotamiton (less effective)
  • Lindane (toxicity concerns; rarely used)
  • Sulfur 5-10% (pediatric, pregnancy alternative)
255.1.0.1.2 Lice (Pediculosis)
255.1.0.1.2.1 3 Types
  • Pediculus humanus capitis (head lice)
  • Pediculus humanus humanus (body lice — also vector for typhus, trench fever, relapsing fever)
  • Phthirus pubis (pubic / crab lice)
255.1.0.1.2.2 Head Lice
  • Children primarily (schools, daycare)
  • Itching at scalp + nape
  • Nits (eggs) attached to hair shafts (resistant to brushing)
  • Live lice on scalp
255.1.0.1.2.3 Body Lice
  • Crowded conditions, war, refugees, homeless
  • Body folds + clothing seams
  • Vector for: epidemic typhus (R. prowazekii — Ch 186), trench fever (B. quintana — Ch 164), relapsing fever (B. recurrentis — Ch 184)
255.1.0.1.2.4 Pubic Lice (“Crabs”)
  • Sexually transmitted typically
  • Pubic + perianal hair
  • Often co-infection with other STIs
  • Eyelash + eyebrow involvement possible (chemical neglect)
255.1.0.1.2.5 Treatment
  • Permethrin 1% lotion / cream (head lice; OTC) — first-line
  • Pyrethrin alternative
  • Malathion 0.5% lotion (resistant cases)
  • Ivermectin lotion (Sklice) — OTC topical
  • Ivermectin PO (200 µg/kg × 2 doses) for severe / resistant / refractory
  • Manual nit removal with nit comb
  • Wash bedding + clothing
  • Body lice: change clothing + treat with permethrin / pyrethrin
255.1.0.1.3 Bedbugs (Cimex lectularius)
255.1.0.1.3.1 Background
  • Small reddish-brown insect; nocturnal blood feeders
  • Recent global resurgence (2000s+)
  • Travel-associated
  • Hotels + crowded housing + shelters
255.1.0.1.3.2 Clinical
  • Linear / clustered pruritic papules (“breakfast, lunch, dinner” pattern — sequential bites)
  • Often on exposed skin (face, neck, arms)
  • Bite reactions vary
  • Not known disease vectors but psychological + social burden significant
255.1.0.1.3.3 Diagnosis
  • Clinical + bite pattern
  • Inspection of mattress / box spring / cracks
  • Pest control
255.1.0.1.3.4 Treatment
  • Topical anti-itch (calamine, low-potency steroid)
  • Antihistamine
  • Pest control + environmental measures (heat treatment, mattress encasement, professional)
  • No specific anti-bedbug medication for humans (treat environment)
255.1.0.1.4 Myiasis (Fly Larvae)
255.1.0.1.4.1 Forms
  • Tumbu fly (Cordylobia anthropophaga) — Africa; clothing line eggs → larvae burrow into skin
  • Bot fly (Dermatobia hominis) — Central + South America; mosquito vector deposits eggs
  • Wound myiasis — flies lay eggs in open wounds
  • Cutaneous myiasis: dermal nodule with breathing hole
255.1.0.1.4.2 Treatment
  • Manual extraction (occlude breathing hole with vaseline → larva emerges)
  • Surgical removal
  • Ivermectin for some (rare); topical / oral
  • Treat secondary infection
255.1.0.1.5 Other Ectoparasites
255.1.0.1.5.1 Chiggers (Trombiculid Mite Larvae)
  • Pruritic dermatitis from larvae attaching to skin
  • Field, grass, brush exposure
  • Self-limited; topical anti-itch
255.1.0.1.5.2 Fleas
  • Cat / dog fleas (Ctenocephalides) — bites; possible vector
  • Rat fleas (Xenopsylla) — plague vector (Ch 161)
  • Cat scratch / sand flea (Tunga penetrans): tropical; female burrows + lays eggs in toe / foot (“tungiasis”); extraction
  • Topical anti-itch + flea control
255.1.0.1.5.3 Ticks (See Ch 185, 186, 187, 188, 221, 222, 223, 224)
  • Lyme, Rocky Mountain Spotted Fever, Babesia, Ehrlichia, Anaplasma, Powassan, etc.
  • Prompt removal critical (within hours for some)
  • Fine tweezers, grasp at skin level, pull straight up
255.1.0.1.6 Insect-Borne Disease Summary
Vector Diseases
Mosquito (Aedes, Anopheles, Culex) Malaria, dengue, Zika, chikungunya, yellow fever, JE, WNV, lymphatic filariasis
Tick (Ixodes, Dermacentor, Amblyomma) Lyme, RMSF, Babesia, Ehrlichia, Anaplasma, Powassan, tularemia
Sandfly (Phlebotomus, Lutzomyia) Leishmaniasis
Tsetse fly (Glossina) African trypanosomiasis (sleeping sickness)
Triatomine bug (kissing bug) Chagas disease
Deer fly (Chrysops) Loiasis
Black fly (Simulium) Onchocerciasis (river blindness)
Body louse (Pediculus) Epidemic typhus, trench fever, louse-borne relapsing fever
Flea (Xenopsylla, others) Plague, murine typhus
Mite (Leptotrombidium chiggers) Scrub typhus