Scabies Clinical Update 2023: Key Insights and Treatment Advances – The Medical Journal of Australia

Introduction

Scabies is a skin infestation caused by the mite Sarcoptes scabiei var. hominis. The World Health Organization recognizes scabies as a leading neglected tropical disease. It primarily affects disadvantaged populations in tropical regions, but outbreaks can occur in crowded settings in wealthier countries, like aged care facilities. This review covers the epidemiology, symptoms, and control strategies for scabies.

Biology

Humans are the only host for Sarcoptes scabiei var. hominis. The mites spread mainly through direct skin contact. Overcrowded living conditions increase transmission rates. Adult female mites are small, about 0.4 mm long, and are not visible. They burrow into the skin, laying two to four eggs daily. The life cycle from egg to adult takes about 10 to 14 days. A person infested with scabies typically carries ten to twelve mites initially.

Epidemiology

Scabies can cause immediate and long-term problems. It leads to significant stigma and psychological issues. The economic impact includes itchiness, sleep disturbance, and missed school or work days. Secondary bacterial infections can arise from skin lesions, leading to conditions like impetigo. In particular, infections with Streptococcus pyogenes can cause severe complications like acute poststreptococcal glomerulonephritis.

Australia’s Indigenous populations are significantly affected, experiencing higher rates of chronic kidney disease related to these infections. Scabies contributes to health disparities, showcasing its impact on broader systemic issues.

Clinical Presentation

Scabies symptoms appear four to six weeks after initial infection. The main symptom is intense itchiness, often worse at night. Lesions typically appear in specific areas, such as between fingers, wrists, and genital regions. Infants may present with vesicles on hands and feet. Skin reactions can worsen with scratching, leading to eczematous changes and secondary infections.

Reinfestation can cause an immediate hypersensitivity reaction, with immune responses observable in the bloodstream. Crusted scabies, a severe form of the infestation, occurs in immunocompromised individuals and requires specialized treatment.

Diagnosis

Diagnosing scabies usually relies on clinical evaluation. Methods include skin scrapings viewed under microscope or dermoscopy to identify burrows. Although more invasive methods exist, they are impractical in many settings. A consensus set of diagnostic criteria helps standardize assessments and improve data collection.

General Management Considerations

Research indicates scabies is mostly transmitted through direct contact. Environmental measures may be less crucial than previously believed. Recommendations still include cleaning linens and personal items, especially for crusted scabies cases. Controlling itchiness through various methods like emollients or topical steroids is also advised.

Institutional Outbreaks

In settings like prisons or aged care facilities, a coordinated response is essential. Identified cases should isolate until treatment is complete. All staff and visitors should take precautions and receive treatment as needed. Children should stay home from school until their treatment starts.

Treatment

Topical permethrin 5% cream is the first-line treatment. It is applied to the body, washed off after eight hours, and a repeat treatment occurs a week later. All close contacts should be treated simultaneously. Alternative treatments include benzyl benzoate, crotamiton, and sulfur ointments.

Ivermectin provides an effective oral option for those who cannot tolerate topical treatments, with specific guidelines for usage. A Cochrane review concluded permethrin is the most effective topical treatment available.

Mass Drug Administration

In regions with high scabies rates, mass drug administration (MDA) of ivermectin is a potential control method. Studies have shown MDA can significantly reduce scabies prevalence in communities. Conflicting data on the effectiveness of single versus multiple doses exist, but some studies suggest a single dose can be sufficient.

Crusted Scabies

Crusted scabies is a severe form involving many mites. Its diagnosis is clinical, often needing skin scrapings for confirmation. Management may require hospitalization, especially in cases with widespread infection. Treatment involves oral ivermectin and topical agents.

Emerging Treatments

New treatments like spinosad have shown promise, but are yet to be researched extensively. Afoxolaner and tea tree oil are being investigated for future use.

Prevention

Preventing scabies involves addressing social factors linked to health disparities. This includes tackling poverty and overcrowded living conditions. Community-based approaches like ivermectin MDA can help reduce infection rates. Empowering communities and educating about scabies transmission are critical for long-term prevention.

Conclusion

Scabies is a persistent global health issue often overlooked. More research is needed to understand its broad impacts and improve diagnostic and therapeutic options. Swift diagnosis and treatment, along with addressing social determinants of health, are crucial to reduce the burden of scabies.