Treatment of Bacterial Infections Caused by Ectoparasites
Ectoparasites such as scabies and lice can be associated with secondary bacterial infections, which should be treated with appropriate antibiotics targeting the most common pathogens—typically Staphylococcus aureus and Streptococcus pyogenes—while simultaneously treating the underlying ectoparasitic infestation.
Primary Management: Treat the Ectoparasite First
The cornerstone of managing bacterial complications from ectoparasites is eradicating the ectoparasite itself, as this removes the source of skin breakdown and bacterial entry 1.
Scabies Treatment
- Permethrin 5% cream applied to entire body from neck down, left on for 8-14 hours, then washed off 2
- Alternative: Ivermectin 200 μg/kg orally as a single dose for cases where topical therapy fails or in institutional outbreaks 1, 2
- Permethrin currently has the best efficacy versus safety profile compared to older agents like lindane 2
Lice Treatment
- Permethrin 1% cream rinse or pyrethrum extract applied to affected areas 3, 2
- Alternative: Ivermectin 200 μg/kg orally for resistant cases 2
- Treatment failures often result from inadequate application time, insufficient coverage, or treating wet hair rather than dry hair 3
Secondary Bacterial Infection Management
When to Suspect Bacterial Superinfection
- Presence of pustules, crusting, weeping lesions, or honey-colored discharge 1
- Fever, regional lymphadenopathy, or cellulitis extending beyond the primary infestation sites 1
- Worsening symptoms despite appropriate ectoparasite treatment 1
Antibiotic Selection for Skin and Soft Tissue Infections
For mild to moderate infections:
- First-line: Cephalexin, dicloxacillin, or other anti-staphylococcal penicillins targeting methicillin-sensitive S. aureus (MSSA) 1
- If MRSA suspected or confirmed: Add vancomycin, daptomycin, linezolid, or ceftaroline 1
- Vancomycin should target serum trough concentrations of 15-20 µg/mL in severe infections 1
For severe infections or immunocompromised patients:
- Broad-spectrum coverage with vancomycin PLUS an anti-pseudomonal beta-lactam (piperacillin/tazobactam, ceftazidime, or carbapenem) 1
- This regimen covers both gram-positive organisms (including MRSA) and gram-negative bacilli that may complicate severe infestations 1
Special Considerations
Crusted (Norwegian) scabies with bacterial superinfection:
- These heavily infested patients are at high risk for severe bacterial complications 1
- Requires aggressive treatment with both systemic ivermectin and topical permethrin, plus appropriate antibiotics for documented bacterial infection 1
- Consider empiric vancomycin if patient is debilitated or immunocompromised 1
Duration of antibiotic therapy:
- Uncomplicated skin infections: 7-10 days 1
- Cellulitis or deeper infections: 10-14 days or until clinical resolution 1
Critical Pitfalls to Avoid
- Do not treat ectoparasites with antibiotics alone—the infestation will persist and bacterial infections will recur 1
- Avoid using lindane due to neurotoxicity concerns; it is no longer recommended in most guidelines 3, 2
- Do not apply permethrin to wet hair as this dilutes the medication and reduces efficacy 3
- Screen and treat household contacts and close contacts to prevent re-infestation, which perpetuates the cycle of skin breakdown and bacterial entry 4
- Differentiate true bacterial infection from inflammatory reactions to the ectoparasite itself, as the latter does not require antibiotics 1