Infectious DiseasesTier 1Disease (DEADMAN)

Common skin infections - parasitic infections, such as head lice and scabies

Description

Head lice (pediculosis capitis) - Pediculus humanus capitis, scalp/hair infestation
Scabies - Sarcoptes scabiei mite burrowing into the epidermis, causing an intensely pruritic hypersensitivity reaction
Crusted (Norwegian) scabies - hyperinfestation variant in the immunosuppressed - highly contagious and a distinct clinical entity

Head lice - common in school-age children, spreads by direct head-to-head contact; does not reflect poor hygiene
Scabies - occurs in all socioeconomic groups; outbreaks common in institutional settings (aged care, remote communities, correctional facilities)
Disproportionately high burden in some remote Aboriginal and Torres Strait Islander communities, linked to overcrowding and driving a downstream burden of post-streptococcal disease via secondary skin infection

Head lice

Direct transmission via head-to-head contact (fomite transmission - combs, hats - much less significant than commonly believed)

Scabies

Direct, prolonged skin-to-skin contact required for transmission (casual contact insufficient) - mite burrows into stratum corneum, lays eggs
Delayed-type hypersensitivity reaction to mite/faeces/eggs drives the intense pruritus, typically 2-6 weeks after primary infestation (faster, within days, on re-infestation due to pre-existing sensitisation)
Crusted scabies: massive mite burden (thousands to millions) due to impaired host immune/hypersensitivity response - immunosuppression, cognitive impairment/reduced ability to scratch, malnutrition

Head lice

Direct visualisation of live lice or viable (near-scalp) nits on wet-combing or examination - distant nits alone (>1cm from scalp) may represent old/hatched cases, not necessarily active infestation

Scabies

Clinical: intense pruritus, worse at night, affecting finger web spaces, wrists, axillae, genitalia, periumbilical area (classic distribution), sparing the face/scalp in adults
Burrows - thin, grey, thread-like lines - pathognomonic when visible but often obscured by excoriation
Dermoscopy ('delta-wing jet' sign) or skin scraping with microscopy confirms mite/eggs/faeces if diagnosis uncertain
Crusted scabies: thick, hyperkeratotic, crusted plaques, may be minimally pruritic despite enormous mite burden - easily missed/misdiagnosed as eczema or psoriasis - a major public health miss given contagiousness

Head lice

Topical pediculicide (e.g. permethrin, or dimeticone as a physical/suffocation-based alternative) applied per product instructions, repeated after 7 days to kill newly hatched lice
Wet-combing as an adjunct/alternative
Treat all affected household/close contacts simultaneously; environmental measures (washing bedding/hats) have a supportive but minor role
No exclusion from school required once treatment started (varies by local policy)

Scabies

Topical permethrin 5% cream - first-line, applied neck-to-toe (whole body in infants/elderly - include face/scalp), left on 8-14 hours, repeated after 7 days
Oral ivermectin - alternative/adjunct, particularly useful for outbreak settings, crusted scabies, or where topical application is impractical; not used in pregnancy, breastfeeding, or children <15kg
Treat all household/close contacts simultaneously regardless of symptoms - essential to prevent re-infestation, given the delayed symptom onset
Wash bedding/clothing used in the preceding few days in hot water; items that cannot be washed can be sealed for 72 hours
Pruritus can persist for 2-4 weeks after successful treatment (post-scabetic dermatitis) - does not necessarily mean treatment failure

Crusted scabies - outbreak-control emergency

Combination therapy: multiple doses of oral ivermectin (e.g. day 1, 2, 8, 9, 15 per severity) plus topical permethrin applied more frequently (e.g. daily to alternate days) and keratolytic agents to reduce crust burden
Strict contact precautions and isolation during treatment - far more contagious than classic scabies
Screen and treat all contacts and the environment aggressively given outbreak potential; public health involvement in institutional settings

Secondary bacterial infection

Treat impetiginised scabies lesions with appropriate antibiotics (see Cellulitis/impetigo note) - important because of downstream post-streptococcal glomerulonephritis risk in high-burden settings

Overcrowded/institutional living - aged care, remote communities, correctional facilities (scabies outbreaks)
Immunosuppression, cognitive/functional impairment - crusted scabies
Secondary bacterial skin infection (impetigo) -> post-streptococcal glomerulonephritis in high-burden settings
School-age children - head lice

Head lice - benign, resolves with treatment; recurrence common with ongoing close contact exposure
Scabies - resolves with appropriate treatment of the patient and contacts; treatment failure usually reflects missed contacts/re-exposure or incomplete application, not resistance
Crusted scabies - major reservoir for institutional/community outbreaks if unrecognised; associated with significant morbidity and, in severe neglected cases, secondary sepsis from extensive skin breakdown
Post-scabetic pruritus can persist for weeks and is often mistakenly treated as ongoing infestation, leading to unnecessary repeat treatment

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