Resistance to scabicides

A strong increase in the number of patients with scabies, a pruritic disease caused by infestation of human skin with scabies mites, has been observed over the last decade, especially in central Europe. In addition, reports on therapy failure after treatment of infested patients with the anti-scabietic substance permethrin have accumulated. This indicate the emergence of resistance of the scabies mites towards permethrin. We recently identified a novel mutation, M918L, in the voltage-sensitive sodium channels of human scabies mites collected from scabies-infested patients in Vienna, Austria. This mutation is known to confer resistance towards permethrin in many insect species. The M918L mutation may not be restricted to scabies mite populations in Vienna, but may also be present in other countries, from which therapy-refractory scabies cases have been reported. In this study, we aim at investigating scabies mites from different countries and continents of the world for the presence of factors associated with loss of sensitivity to permethrin and other substances. For this purpose, scabies mites derived from other parts of Austria and other countries will be collected and investigated for the presence of the M918L mutation as well as other mutations in the voltage-sensitive sodium channels known to confer resistance. In addition, the expression, transcription and activity of certain enzymes, termed glutathione S-transferases, which are responsible for the detoxification of anti- scabietic substances, will be determined in the mites. The presence of both, mutations and alterations in the enzyme levels may explain the loss of sensitivity to the anti-scabietic substances and the increasing numbers of therapy-refractory scabies cases. It is conceivable that the widespread use of scabicides, particularly of permethrin, in humans in the recent past has driven selection towards resistance in the mites. Monitoring the susceptibility to anti-scabietic substances to detect early levels of resistance and surveillance of the spread and evolution of resistant mites are urgently warranted. The results of this study may contribute to optimize the treatment of scabies-infested patients not only in Austria, but also in Europe and other countries across the globe and may have an impact on international control programs on scabicide and insecticide resistance.