Increased Monooxygenase Activity Associated with Resistance to Permethrin in <I>Pediculus humanus capitis</I> (Anoplura: Pediculidae) from Argentina

Abstract

We studied the profile of permethrin resistance in populations of head lice infesting children 6-12 yr old in schools and their homes in and around Buenos Aires, Argentina. Five permethrin-resistant populations with different levels of resistance were collected: Hogar Loyola (HL), Republica de Turquia (RT), Hogar Mitre (HM), Guardia de Honor (GH), and Ricardo Guiraldes (RG). One susceptible population, Bandera Argentina (BA), also was collected. Their level of resistance was evaluated, and results showed resistance ratios of 13 for HL, 16 for RT, 22 for HM, 61 for GH, and 69 for RG. To elucidate the possible involvement of the cytochrome P450 monooxygenase system in conferring permethrin resistance, ethoxycoumarin-O-deethylase (ECOD) activity was measured in abdomens of individual third instars and adults by using a fluorometric assay. The ECOD activity was lower in the susceptible BA population (4.7 ng per louse) than in the resistant ones (13.7 ng per louse for RG, 12.3 ng per louse for GH, 8.6 ng per louse for RT, and 8.2 ng per louse for HL). ECOD activity was significantly correlated with the level of resistance in the field populations (r = 0.97, P = 0.0009), suggesting a role for cytochrome monooxygenase P450 system in permethrin resistance by head louse, Pediculus humanus capitis De Geer.

Activity of increased specific and non-specific esterases and glutathione transferases associated with resistance to permethrin in pediculus humanus capitis (phthiraptera: pediculidae) from Argentina

“…However, the high levels of resistance we observed cannot be explained only in terms of detoxifying enzymes, even considering esterase and oxidase activities. A positive correlation was observed between the levels of monooxygenase and resistance to pyrethroids (Gonzalez Audino et al 2005), but the present results suggest there is another mechanism of permethrin resistance in these populations. This leads us to consider the presence of a modified voltagedependant sodium channel (a kdr-type mechanism).…”

“…These populations were named according to the district from which they were collected: BA, GH, RT, RG, HL and HM. The resistance ratio of these populations has been previously characterized (González Audino et al 2005), but as the application of insecticides in schools is highly variable from year to year, we decided to determine the current levels of resistance.…”

“…In a previous study, we demonstrated the importance of enhanced metabolism by monooxygenases in head louse populations from Buenos Aires, Argentina, that exhibited different levels of resistance to permethrin. A positive correlation was established between enzyme activity and permethrin lethal dose 50 (LD 50 ) in the resistant populations (Gonzalez Audino et al 2005).…”

Prevalence ofkdr-like Mutations Associated with Pyrethroid Resistance in Human Head Louse Populations in Japan

“…However, we should consider the development of metabolic resistance through the activities of carboxyl esterase and cytochrome P450 monooxygenases. Involvement of cytochrome P450 in the development of resistance in the head louse colonies obtained from Argentina was suspected because of a high correlation between LD 50 to permethrin and P450-mediated ethoxycoumarin O-deethylase (ECOD) activity (Audino et al 2005) and also because of synergism of a P450 inhibitor, piperonyl butoxide (Picollo et al 2000). At the time of receiving the head louse samples, we also distributed questionnaires to the hosts as a tool to collect information regarding the effectiveness of phenothrin.…”

Plant extracts and their components as potential control agents against human head lice

“…Moreover, there have been several reports of evolution of resistance to the conventional insecticides that are usually included in formulations (i.e., pyrethroids, lindane) (Burkhart et al 1998;Picollo et al 1998;Levot 2000;Jones and English 2003;Yoon et al 2004). Such resistance appears to be associated to a variety of biochemical traits, including a mechanism based on glutathione S-transferase (GST) for resistance to DDT (Miller and Mumcuoglu 1999;Namazi 2005), the cytochrome monooxygenase P450 system for permethrin (Audino et al 2005), estearase activity for dual resistance to malathion and permethrin (Gao et al 2006), and sodium channel-mediated resistance to pyrethroids (Tomita et al 2005). The universe of treatments has been further decreased since some insecticides that had been successfully used in the past (DDT, gamexan, carbaryl) were fortunately withdrawn as anti-lice products in some countries, due to their high toxicity (Burkhart et al 1998).…”