DR5.1,DR6.1 | Ectoparasitic Infestations — Graded Quiz

Correct. Crusted scabies carries millions of mites; topical scabicide monotherapy is frequently insufficient due to poor penetration of thick hyperkeratotic crust. Combination oral ivermectin (repeated dosing at Days 1, 2, 8, 9, and 15 in severe cases) plus topical permethrin 5% is the standard approach. All contacts and healthcare workers must be treated simultaneously due to extreme contagiousness.

Crusted (Norwegian) scabies in immunocompromised patients requires combination treatment (oral ivermectin + topical permethrin) due to the massive mite burden. Standard topical monotherapy is insufficient. Strict contact precautions and simultaneous treatment of all contacts are mandatory.

Correct answer is B. Crusted scabies requires combination therapy (ivermectin + permethrin) not topical monotherapy. The nurses have already been exposed and must be treated immediately — not after developing burrows.

Correct. Sarcoptes scabiei survives off-host for only 24-36 hours under normal conditions. Therefore, washing clothing and bedlinen at ≥50°C or using a hot dryer, plus sealing non-washable items (e.g., soft toys, coats) in plastic bags for 72 hours, is sufficient. Items need not be dry-cleaned; the 72-hour sealing method is practical and effective. Routine room fumigation or acaricide spraying is not recommended or evidence-based.

Environmental decontamination for scabies: Sarcoptes mites survive off-host for up to 24-36 hours (not weeks). Washing clothing/bedlinen in hot water ≥50°C (or sealing non-washable items for 72 hours) is effective. Routine room fumigation is not required.

Correct answer is B. Hot-water washing (≥50°C) of bedlinen/clothing and sealing non-washable items for 72 hours is the evidence-based environmental measure. Mites survive only 24-36 hours off-host, so room fumigation is not needed.

Correct. Nodular scabies results from granulomatous hypersensitivity to mite antigens (dead mite parts, faecal pellets) persisting in dermal nodules. Characteristic sites are axillae, groins, and genitalia. The absence of new burrows and confirmed adequate treatment of all contacts confirms successful eradication of live mites. Management is potent topical corticosteroids or intralesional triamcinolone, not re-treatment with scabicide.

Nodular scabies is a post-scabetic hypersensitivity reaction (granulomatous inflammation) occurring at sites of prior heavy infestation (axillae, groin, genitalia). Nodes can persist months after successful treatment. No live mites are found. Management is intralesional or potent topical corticosteroids, NOT re-treatment.

Correct answer is B. Nodular scabies = persistent hypersensitivity granulomas after successful treatment. No new burrows + all contacts treated = not reinfestation. Lindane is especially contraindicated in a 3-year-old.

Correct. In pediculosis corporis, the lice and their eggs are found in clothing seams, not on the skin. Therefore, the definitive treatment is treating or discarding the clothing and bedding (hot washing, dry cleaning, or sealing), combined with improvement of personal hygiene. Topical application of pediculicide to the skin is not the primary treatment, as this misses the reservoir. Systemic antibiotic (doxycycline) for Rickettsia is indicated only if typhus is clinically suspected — not routinely.

Pediculosis corporis: lice live in clothing seams, not on skin. Treatment is delousing/discarding clothing and improving personal hygiene — NOT a topical pediculicide applied to skin. The skin itself needs only symptomatic treatment.

Correct answer is B. P. corporis lives in clothing, so treating the clothing (not just the skin) is the definitive approach. Applying permethrin to scalp or full-body skin addresses the wrong reservoir.

Correct. Phthirus pubis is transmitted by close sexual contact. All sexual contacts within the past month must be treated simultaneously with the index case, whether or not they have symptoms. Waiting for symptoms risks reinfestation. Additionally, the adolescent should be offered screening for other STDs, and privacy/confidentiality in counselling is essential.

Pediculosis pubis is an STD. All sexual contacts within the preceding month should be treated simultaneously with the index case, regardless of whether they are symptomatic, to prevent reinfestation. The incubation period with no symptoms can be 1-4 weeks.

Correct answer is B. Sexual contacts within the preceding month must be treated simultaneously — asymptomatic contacts can harbour lice in the pre-sensitisation phase and will reinfest the index case if not treated.

Correct. Oral ivermectin is dosed at 200 mcg/kg (not 400). Food (particularly fatty food) significantly enhances oral bioavailability. A second dose 2 weeks later is recommended to kill mites that have hatched from eggs after the first dose (ivermectin has limited ovicidal activity). Ivermectin is NOT recommended in pregnancy (FDA Category C), children <15 kg, or patients with CNS disorders.

Oral ivermectin for scabies: dose 200 mcg/kg (NOT 400), ideally with food (fatty meal increases absorption). A second dose after 2 weeks is recommended because ivermectin kills live mites but has limited ovicidal activity. Contraindicated in pregnancy.

Correct answer is B. The dose is 200 mcg/kg (not 400). Food improves absorption. A repeat dose at 2 weeks is needed due to limited ovicidal activity. It is NOT safe in pregnancy.

Correct. The presence of live lice on wet-combing is the definitive confirmation of active infestation. Hair grows approximately 1 cm/month; nits found >1 cm from the scalp were likely laid more than 1 month ago and may represent dead nits from a previously treated or resolved infestation. Nits alone (without live lice) are not sufficient to confirm active infestation requiring treatment.

Active pediculosis capitis is confirmed by live lice. Nits present >1 cm from scalp are likely non-viable (old or post-treatment). Nits <1 cm from scalp are more likely viable. Live louse = definitive active infestation.

Correct answer is B. Live lice on wet-combing is the gold standard for confirming active, current infestation. The distance of nits from the scalp is a supplementary clue — nits >1 cm are likely old/non-viable.

Correct. Nit casings (empty shells) remain firmly cemented to hair shafts after successful treatment because the adhesive glue is not dissolved by pediculicides. As hair grows (~1 cm/month), these casings are progressively displaced distally. At 3 weeks they would be approximately 3 cm from the scalp — consistent with non-viable residual casings. No live lice on wet-combing is reassuring evidence of treatment success. Re-treatment is not indicated on the basis of nit shells alone.

Empty nit casings (nit shells) remain glued to hair shafts after successful treatment. They do not fall off spontaneously. Hair grows ~1 cm/month, so nits seen at 3 weeks are likely >3 cm from scalp — old, non-viable. No live lice on wet-combing = treatment success.

Correct answer is B. Residual nit casings are normal after successful treatment — they remain glued to hair and grow out with it. No live lice on wet-combing confirms treatment success.

Correct. When permethrin 1% fails (clinical resistance), the two main second-line alternatives are: (1) malathion 0.5% lotion — an organophosphate pediculicide with a different mechanism (irreversible cholinesterase inhibition); and (2) oral ivermectin 200 mcg/kg repeated at 7-10 days (to catch newly hatched nymphs). Both have evidence for efficacy against permethrin-resistant strains. Lindane is avoided in children due to neurotoxicity.

For permethrin-resistant pediculosis capitis, second-line options include malathion 0.5% (organophosphate, different mechanism) or oral ivermectin (especially for widespread/resistant cases). Lindane is not recommended in children. Benzyl benzoate undiluted is irritant.

Correct answer is B. Malathion 0.5% or oral ivermectin are the appropriate second-line choices. Lindane is contraindicated in children. Higher-concentration permethrin does not overcome pyrethrin-resistance mechanisms.

Correct. Evidence-based community management focuses on: (1) treating confirmed cases (permethrin 1% × 2 doses); (2) screening and treating household contacts and close classmates with live lice; (3) health education on transmission prevention (avoiding head-to-head contact, not sharing combs, brushes, hats). School closure is not recommended by major guidelines and creates unnecessary stigma. Mass prophylactic treatment exposes uninvested children to drug risk without benefit.

Community management of pediculosis capitis: treat confirmed cases + screen/treat contacts. School exclusion policies vary — most evidence does NOT support 'no-nit' policies or school closure. Education on prevention (no head-to-head contact, no sharing combs/hats) is key. Mass prophylactic treatment is not recommended.

Correct answer is B. Evidence-based approach: treat confirmed cases with permethrin 1% (2-dose), screen contacts, educate on prevention. School closure and mass prophylaxis are not recommended.