Management of Pyrethroid Resistance in Head Louse Populations

MARÍA INÉS PICOLLO

Urgup, Cappadocia

Congreso; 9. Fourth International Conference on Phthiraptera (ICP4); 2010

International Society of Phthirapterists

In Argentina, the infestation with Pediculus humanus capitis is an endemic sanitary problem affecting 30% of school-aged children. Moreover, more than 90% of head louse populations have developed high levels of resistance to permethrin (28.6-71.4) and other pyrethroids. As a consequence, there had been a trend to the use of herbal remedies for the control of pyrethroid-resistant head lice. First studies demonstrated that the essential oils from natural aromatic plants from Argentina produced differential fumigant toxicity against head lice. Similarly, the terpenoid constituents of the effective essential oils, also demonstrated differential activity. Additionally, some whole oils resulted more active than any of its individual components. In order to improve the use of these natural compounds as pediculicides, we investigated the physiochemical parameters related with the activity of the monoterpenoids, as well as the toxic interactions of the components that affect the activity of the mix. A positive relationship was found between the fumigant efficacy of the compounds and the corresponding vapor pressures. The more volatile compounds were more effective fumigants against lice and also against their eggs, indicating that these compounds could be incorporated into formulations as potential pediculicides against both stages. Moreover, a clear correlation was established between the viscosity and the contact toxic effect. It was a non-linear relationship which demonstrated the highest pediculicide potency at a medium range of viscosities. This means that the pediculicidal activity could be improve modifying the viscosity of the formulation. The individual components of Argentinean plants varied in their activity when they were evaluated alone or mixed (in the same natural ratio) with other components of the whole oil. For example, a clear synergism was established by topical application between pulegona and citral (the major components of Aloysia citriodora), and between citronelol, linalol and citronellol from the geranium oil. These interactions were also found in pediculicide formulations and lead the development of a commercial product based on the synergized monoterpenes. All this knowledge represents important tools to design novel strategies to improve the overall management of head louse infestations.