What is the best treatment approach for a patient with a body lice infestation, previously treated with permethrin, who did not treat their belongings and sleeps at a shelter, should I repeat permethrin or trial ivermectin with treating all clothing and belongings?

Treatment Approach for Body Lice with Treatment Failure

Switch to oral ivermectin (200 μg/kg, repeated in 2 weeks) AND simultaneously implement comprehensive environmental decontamination of all clothing and bedding, as repeating permethrin alone will likely fail without addressing the untreated fomites that are causing reinfection. 1

Why Ivermectin Over Repeating Permethrin

The primary issue here is not treatment failure but reinfection from untreated belongings. However, given the shelter setting and documented permethrin resistance patterns, switching to ivermectin offers several advantages:

• Oral ivermectin eliminates the need for proper topical application, which is particularly challenging in shelter settings where bathing facilities may be limited 2
• Ivermectin demonstrated dramatic efficacy in homeless populations with body lice, reducing lice burden from 1,898 to 6 lice over 14 days in a shelter cohort 2
• The two-dose regimen (days 1 and 8-14) addresses ivermectin's limited ovicidal activity, ensuring newly hatched nymphs are killed 1
• Ivermectin should be taken with food to increase bioavailability and epidermal penetration 1, 3

Critical Environmental Measures (Non-Negotiable)

Environmental decontamination is absolutely essential and was the primary reason for treatment failure:

• Machine-wash and machine-dry all clothing and bedding using the hot cycle, or dry-clean them 1
• Alternatively, remove items from body contact for at least 72 hours, as body lice cannot survive off the host beyond this period 1
• Coordinate with shelter staff to ensure the patient has access to clean clothing and bedding immediately after treatment 4
• Fumigation of living areas is NOT necessary 1

Treatment Protocol

Day 1:

• Administer ivermectin 200 μg/kg orally with food 1, 3
• Provide clean clothing and bedding immediately
• Decontaminate all current clothing/bedding

Day 8-14:

• Repeat ivermectin 200 μg/kg orally with food 1, 2
• Verify environmental measures were maintained

Day 15:

• Follow-up evaluation to confirm eradication 1

Why Not Repeat Permethrin

Repeating permethrin without environmental measures will fail again:

• Body lice live primarily on clothing, not on the body, traveling to skin only for blood meals 4, 5
• Permethrin resistance is increasingly widespread, though specific resistance patterns vary geographically 1
• Topical application requires proper bathing facilities and technique, which may be limited in shelter settings 5
• The patient already failed permethrin once, suggesting either resistance, improper application, or reinfection from fomites 1

Common Pitfalls to Avoid

Do not treat the patient without simultaneously addressing environmental decontamination - this is the most common cause of apparent "treatment failure" 1, 4

Do not assume treatment failure is due to resistance alone - untreated clothing/bedding is likely the primary issue here 4

Do not use lindane - it has significant neurotoxicity risk and should only be used when other therapies fail or cannot be tolerated 1

Do not expect immediate symptom resolution - pruritus may persist for up to 2 weeks after successful eradication due to hypersensitivity reactions 6

Special Considerations for Shelter Settings

Coordinate with shelter staff to ensure:

• Access to laundry facilities or provision of clean clothing 4
• At least once-weekly bathing opportunities 4
• Screening of other shelter residents who may be infested 4

Body lice prevalence ranges from 4.1% to 35% among persons experiencing homelessness, making this a common issue requiring systematic approaches 4