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

Kate E. Mounsey; Deborah C. Holt; James McCarthy; Bart J. Currie; Shelley F. Walton

Disclosures

Future Microbiol. 2008;3(1):57-66. 

In This Article

Ivermectin Resistance

After nearly 30 years of intensive use, ivermectin resistance is now widespread in veterinary practice, and may now be emerging in filarial nematodes affecting humans.[36] There is now data suggesting that on a genetic level, ivermectin is imposing selection pressure on several Onchocerca volvulus genes.[37]

Ivermectin has been used for over 10 years for the management of crusted scabies in northern Australia. One patient with recurrent crusted scabies has received approximately 150 doses of ivermectin over a 13-year period, arguably the highest in the world. Since its introduction, treatment failures have been observed with ivermectin therapy for crusted scabies, despite intensive multiple-dose regimens ( Box 1 ). Clinical and in vitro ivermectin resistance has now been documented in two crusted scabies patients.[21] Significantly, these were the first reports of ivermectin resistance in scabies. Furthermore, analysis of 10 years of in vitro sensitivity data shows that median survival times to ivermectin have doubled since its introduction.[38]

Although these latter clinical cases currently appear to be isolated events, they do highlight the future uncertainty regarding the long-term usefulness of ivermectin for the treatment of scabies, especially in severe cases and in endemic regions where community-based treatment may be desired. An important consideration is that crusted scabies patients are often identified as core transmitters of scabies to others in the community, and therefore the spread of ivermectin resistant mites may jeopardize the success of future mass treatment strategies involving ivermectin.

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