π Stepwise Approach to Arthropod Infestations
π Key Principles β Nelson Chapter 709
β’ Scabies (Sarcoptes scabiei): Intense pruritus (worse at night), burrows (finger webs, wrists, axillae, genitalia), papules, vesicles, nodules. Infants: palms, soles, scalp. Treatment: Permethrin 5% cream (first-line) β apply neck down, wash off 8-14h; repeat in 1 week. Ivermectin (200 ΞΌg/kg) for crusted or resistant. Treat all contacts.
β’ Norwegian (crusted) scabies: Hyperinfestation in immunocompromised, Down syndrome, elderly. Thick crusts, scales. Highly contagious. Treat with permethrin + oral ivermectin.
⒠Head lice (Pediculus humanus capitis): Pruritic scalp, nits on hair shafts (occipital, retroauricular). Treatment: Permethrin 1% crème rinse, pyrethrins, malathion 0.5%, ivermectin lotion, benzyl alcohol, spinosad. Comb nits, wash bedding in hot water.
β’ Body lice (Pediculus humanus corporis): Homelessness, poor hygiene. Pruritus, excoriations, hyperpigmentation ("vagabond's skin"). Lice and nits in clothing seams. Treat by improving hygiene and laundering clothes.
β’ Pubic lice (Phthirus pubis): Sexually transmitted. Pruritus, nits on pubic/axillary/eyelash hair. Pyrethrins or permethrin. Treat sexual partners.
β’ Bed bugs, fleas, mosquitoes: Papular urticaria, grouped lesions (3-4 in line). Diagnosis clinical. Symptomatic treatment: antihistamines, corticosteroids. Eradicate source.
β’ Seabather's eruption: Thimble jellyfish larvae. Pruritic dermatitis under swimsuit. Topical corticosteroids, antihistamines.