Scabies: Molecular Perspectives and Therapeutic Implications in the Face of Emerging Drug Resistance

Authors and Disclosures

Kate E. Mounsey, Charles Darwin University, Menzies School of Health Research, Darwin, Northern Territory, Australia Tel: +61 889 228 599; Fax: +61 889 275 187; Kate.mounsey@menzies.edu.au

Deborah C. Holt, Charles Darwin University, Menzies School of Health Research, Darwin, Northern Territory, Australia Tel: +61 889 228 599 Fax: +61 889 275 187; deborah.holt@menzies.edu.au

James McCarthy, Queensland Institute of Medical Research & Australian Centre for International & Tropical Health & Nutrition, University of Queensland, Brisbane, Queensland, Australia Tel: +61 738 453 796; Fax: +61 733 620 104; j.mccarthy@uq.edu.au

Bart J. Currie, Charles Darwin University, Menzies School of Health Research, Darwin, Northern Territory, Australia and, Northern Territory Clinical School, Flinders University, Darwin, Northern Territory, Australia. Tel: +61 889 228 056; Fax: +61 889 275 187; bart.currie@menzies.edu.au

Shelley F. Walton, Charles Darwin University, Menzies School of Health Research, Darwin, Northern Territory, Australia Tel: +61 889 228 928; Fax: +61 889 275 187; shelley.walton@menzies.edu.au

Financial & competing interests disclosure: The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Sidebar: Executive Summary

The Problem With Scabies

• Scabies remains a significant health problem, especially in developing and disadvantaged populations. The apparent link between scabies and complications of streptococcal pyoderma has led to concerted efforts to reduce rates of scabies in northern Australian Aboriginal communities.

Therapeutic Options

• Difficulties with diagnosis and a lack of quality clinical trials make it difficult to evaluate optimal therapeutic strategies for scabies. The first-line treatment in many countries is now 5% permethrin, with ivermectin, a promising oral therapy for ordinary scabies. Benzyl benzoate continues to be highly efficacious, although there are problems with its tolerability. Tea tree oil looks promising as a new topical therapy.

Threats of Resistance

• Clinical and in vitro resistance to ivermectin has now been documented and there are concerns regarding the increasing tolerance of scabies mites to permethrin.
  
  

• There is an urgent need to define molecular mechanisms of drug resistance in order to detect its emergence more rapidly, providing more options to control its spread.

Recent Molecular Advances

• New molecular studies are shedding light on potential drug resistance mechanisms in scabies mites. Several key molecules have been characterized, including the permethrin-sensitive sodium channel gene, an ivermectin sensitive ligand-gated chloride channel, and several ABC transporter genes and glutathione S-transferases.

Future Perspective

• A rigorous evaluation of all currently available acaricides via clinical trials may provide acceptable alternative therapeutic options in the face of emerging drug resistance.
  
  

• More needs to be understood regarding ivermectin pharmacokinetics in relation to optimal treatment for both ordinary and crusted scabies. Safety issues regarding the use of ivermectin in children less than 15 kg and in pregnancy should be addressed in clinical studies.
  
  

• Continued molecular advances, coupled with laboratory drug selection studies in animal models, will greatly enhance our understanding of acaricide resistance in scabies mites and will provide more sensitive tools for diagnosis and control of resistance.