Pediculicidal activity of binary mixed monoterpenoids on head lice

EUNICE E. SOSA-QUIROGA, AGUSTINA B. FAÑANI, ALEJANDRO LUCIA, EDUARDO GUZMÁN, ARIEL C. TOLOZA

Guangzhou

Conferencia; 7 th International Conference on Phthiraptera; 2023

Institute of Zoology, Guangdong Academy of Sciences

Essential oils are a special group of chemical compounds belonging to the natural products, which are in general highly volatile substances obtained from a wide variety of sources. The different components of essential oils have different physicochemical properties and possess an extraordinary bioactivity against head lice. The combination of monoterpenoids with an adjuvant can enhance efficiency and be environmentally friendly. In Argentina, pediculosis infestation is around 30% and most of the head lice are resistant to permethrin. The aim of this study was to study the pediculicidal activity of nanoformulations containing mixed monoterpenoids in comparison with pure compounds. Adult head lice were obtained from infested children or elementary schools from Buenos Aires. The monoterpenes used were eugenol, 1,8-cineol, linalool and thymol, prepared by stirring poloxamer at variable concentrations. The binary mixtures were: eugenol-linalool (1), 1,8-cineol-linalool (2), and eugenol-thymol (3) in proportions 3:1, 1:1, 1:3. We evaluated the insecticidal activity by the immersion bioassay of the different nanoformulations and the base formulation consisted of 5wt% polaxamer 407 aqueous solution was used as control. The knockdown time that affects 50% of the individuals (KT50) expressed in hours was determined. To establish the type of interaction between each mixture, the combination index (IC) was estimated using the CompuSyn software. The KT50 values obtained from the pure compounds were linalool 6.07; 1,8-cineol 8.83; eugenol 7.17 and thymol 27.23h. All the binary mixtures (1) had an effectiveness less or equal to the nanoformulations of the pure compounds with values of 13.33, 8.16 and 6.71h in the proportions 3:1, 1:1, 1:3. The binary mixtures (2) had similar values: 10.02; 8.16 and 6.71h. In addition, the 1:1 and 1:3 ratios of the binary mixtures (3) presented values of 9.40 and 32.93h, while the 3:1 ratio showed the greatest effectiveness with a value of 4.42h. The IC determined for the mixture (1) was >1 showing an antagonistic interaction, and the combination 3:1 had the strongest antagonistic interaction. The binary mixtures (2) had ICS≃1, suggesting an additive interaction for all the mixes. For the binary mixtures (3) an IC< 1 was determined for the combinations 3:1 and 1:1 indicating a synergistic interaction, while the 1:3 combination of the same mix did not show any interaction. This study suggests that eugenol stabilizes linalool by decreasing its effectiveness, while 1,8-cineol does not significantly affect linalol. On the other hand, thymol acts as a synergist, enhancing the activity of eugenol. These results are an important contribution in the development of pediculicidal nanoformulations based on botanical compounds.