Scabies, Bedbug, and Body Lice Infestations
SUMMARY:
Scabies, bedbugs, and body lice are all common ectoparasitic diseases that cause similar dermatologic reactions of pruritis and rash. In most cases, a careful history and physical exam can differentiate the three from one another to ensure appropriate therapy. Scabicides are first-line treatment for patients with scabies and their close contacts. All ectoparasitic infestations must be eradicated with decontamination measures to prevent persistent disease and spread.
Table of Contents
KEY POINTS:
Scabies
Pathophysiology
- Caused by an infestation of the mite Sarcoptes scabiei var hominis
- Mites live in the human epidermis and cause a delayed skin hypersensitivity reaction 4-6 weeks after eggs hatch
- Transmission typically requires 15-20 minutes of direct skin-to-skin contact
- Transmission risk is increased in overcrowded shared living spaces, such as shelters, child-care centers, carceral settings, and long-term care facilities
Clinical Presentation
- Classically presents with pruritic, curvilinear lesions ending in an erosion or vesicle on the webbing of fingers and toes, volar wrists, ankles, axillae, buttocks, male genitalia, and areolae.
- Severely pruritic, often leading to excoriations | lichenifications | superinfection with bacteria such as Staphylococcus aureus
- These findings can mimic other dermatologic disease, such as eczema or urticaria
Diagnosis
- Mites are microscopic and not visible to the naked eye at any point in their life cycle
- Skin scraping for microscopy can be performed by putting a drop of mineral oil on a sterile surgical blade and scraping the skin
- 2020 International Alliance for the Control of Scabies consensus criteria for scabies diagnosis:
- Confirmed diagnosis requires microscopic evidence of mites | eggs | feces
- Clinical diagnosis:
- Burrows or typical lesions in male genital area or typical lesions in typical distributions and 2 positive historical findings (itch |positive contact history)
- Suspected diagnosis:
- Typical lesions in a typical distribution and 1 historical feature or atypical lesions/atypical distribution and 2 historical features
- In the case of clinical or suspected scabies, treatment is reasonable if other differential diagnoses are less likely than scabies
Treatment
- Topical permethrin 5% cream is the most effective treatment for scabies.
- Can be used for patients 2 months of age and older
- Common adverse effects include skin irritation and itching, which may limit use.
- Oral Ivermectin used if topical therapy administration not feasible due to lack of privacy or skin irritation
- Other treatments include crotamiton 10% cream or lotion | spinosad 0.9% topical suspension
- Treat clothes and linens by washing in hot water or enclosing in a plastic bag for at least 72 hours to avoid fomite transmission
- All close contacts of patients with scabies should be treated even if asymptomatic
Bedbugs
Pathophysiology
- Caused by infestation of insects in the Cimicacidae family
- Insects take blood meals from humans throughout the insect life cycle
- Blood meals lead to skin reactions
- Thrive in warm, dark environments e.g. mattresses| furniture | flooring | walls
- Visible to the naked eye
- Often infest areas with high turnover | hotels | motels | hostels | shelters
Clinical Presentation & Diagnosis
- Pruritic, erythematous papules on exposed areas
- New lesions on awakening (bedbugs are nocturnal
Treatment
- Primary treatment is to eradicate the infestation with professional treatment
- Skin reactions typically resolve on their own after 1 week
- Midpotency topical corticosteroids can be used for symptom control
Body Lice
Pathophysiology
- Caused by infestation of the body lice in individuals who are unable to maintain personal hygiene, such as persons experiencing homelessness | displacement | mental illness
- Live on clothing and visible to the naked eye
- Take blood meals from humans leading to hypersensitivity reaction | pruritis
Clinical Presentation
- Erythematous macules | papules| plaques with associated excoriations and occasional hyperpigmentation or lichenification
- Typically located where clothing seams touch the skin: waistline | medial and lateral legs | upper back
- Secondary bacterial infections have been demonstrated in some populations
Treatment
- First-line treatment is eradication of the infestation with regular bathing and laundering
- Oral ivermectin or topical permethrin can be considered for individuals who are unable to maintain regular hygiene, though their effectiveness is limited
- Mid-potency topical corticosteroids e.g. triamcinolone 0.1% can be used for symptom control if needed
