A comprehensive survey of permethrin resistance in human head louse populations from northwest Iran: ex vivo and molecular monitoring of knockdown resistance alleles

Abstract

Background Head louse infestation is an important public health problem, and expanding resistance to permethrin is a major challenge to its control. The mapping and detection of pyrethroid resistance are essential to the development of appropriate treatments and ensure the effectiveness of current measures. The aim of this study was to present the phenotypic and genotypic basis of permethrin resistance and identify knockdown resistance (kdr) mutations in head louse populations in northwestern Iran. Methods Adult head lice were collected from 1059 infested girls in Ardebil, East Azerbaijan, West Azerbaijan and Zanjan Provinces, northwestern Iran. The toxicity of permethrin and the possible synergistic effect of piperonyl butoxide (PBO) on this toxicity were assessed using bioassays. Fragments of voltage-sensitive sodium channels (vssc) and cytochrome b (cytb) genes were amplified and analyzed for the detection of knockdown resistance (kdr) mutations and mitochondrial groups. Moreover, genotypes of the two hot spot regions of the vssc gene were determined by melting curve analysis of amplicons. Results A total of 1450 adult head lice were collected during 2016–2021. Live lice were exposed to a dose of 1% permethrin for 12 h, and the median lethal time (LT50) and time to achieve 90% mortality (LT90) were determined to be 6 and 14.8 h, respectively. Topical application of 2 and 16 ng permethrin per louse resulted in 25% and 42.11% mortality, respectively. Pre-exposure of samples to 3% piperonyl butoxide had no synergistic effect on the effects of permethrin. Analysis of the 774-bp vssc gene fragment showed the presence of the M815I, T917I and L920F mutations, wild-type and T917I mutation, in 91.6%, 4.2% and 4.2% of samples, respectively. Investigation of the mitochondrial cytb gene demonstrated the predominance of clade B. The frequency of domain II segment 4 (S4)-S5 kdr genotypes in mitochondrial groups was identical, and heterozygotes were present in 93.5% of samples. A significant difference was detected in the frequency of domain IIS1-S3 kdr genotypes, and the frequency of resistant alleles and heterozygotes was higher in clade B than in clade A. Conclusions The presence of kdr mutations in the vssc gene and the non-synergist effect of PBO indicate that pyrethroid target site insensitivity is the main resistance mechanism. This phenomenon and the high frequency of resistant alleles necessitate that new pediculosis management programs be developed. Further studies need to be conducted to identify all factors contributing this resistance and to develop alternative pediculicides. Graphical Abstract

Epidemiological analysis of pediculosis and the distribution of kdr mutation frequency in head lice populations in Khorasan Razavi Province, northeastern Iran

“…Recently, the identi cation of kdr amino acid substitutions, including M815I, T917I, and L920F, has been supplemented by the discovery of six new mutations within the extracellular loops of IIS1-2 (H813P) and IIS5 (I927F, L928A, R929V, L930M, and L923M), as well as the mutation F815I in head lice and the mutation N818D in body louse populations across the country. These alpha subunits have been demonstrated to be strongly linked with kdrresistance, and the presence of the F815I and N818D mutations has also been documented (Firooziyan et al, 2017;Ghavami et al, 2023). In the course of the present study, however, a total of four novel amino acid substitutions-namely, K794E, P813H, F815I, and N818Dwere identi ed in head lice for the very rst time.…”

“…Examination of the kdr gene sequence in head lice within the purview of THUMS revealed the presence of haplotype I (M815I + T917I + L920F), which has previously been documented in Iran (Firooziyan et al, 2017;Ghahvechi Khaligh et al, 2021;Ghavami et al, 2023). A novel haplotype was also identi ed in the region, constituting the fth kdr haplotype in head lice.…”

“…Despite the application of dimethicone and 1% permethrin for the treatment of head lice in the study area during both 2016 and 2017, the incidence of infestations demonstrated a notable 24% increase. Conversely, in various studies, the use of 1% permethrin exhibited effectiveness, ranging from 29-90%, after treatment periods of one, two, and three weeks (Moemenbellah-Fard et al, 2016;Firoozfar et al, 2019;Ghavami et al, 2023). Direct, face-to-face training on the proper application of anti-lice compounds has been demonstrated to be effective in enhancing their effectiveness.…”

“…To address this concern, consistent monitoring of the resistance status becomes imperative to identify suitable insecticides for effective control measures. The global prevalence of insecticide usage has resulted in reported instances of insecticide resistance in various parts of the world (Chosidow et al, 1994;Rupes et al, 1995;Picollo et al, 1998;Downs et al, 1999;Hemingway et al, 1999;Pollack et al, 1999;Ghavami et al, 2023;Kitvatanachai et al, 2023). The annual increase in the number of infestation cases within the population encompassed by THUMS, despite concerted efforts, could stem from the emergence of resistance within the region.…”

Evaluation of resistance of human head lice to pyrethroid insecticides: A meta-analysis study

“…Ebrahimi et al (2021) in Iran identified three kdr point mutations in amino acids D820E, L840F, and N874G, corresponding to the replacement of aspartic acid to glutamic acid, leucine to phenylalanine, and asparagine in the human head louse population, which L840F was identified as a new mutation [ 49 ]. Ghavami et al (2023) reported the presence of M815I, T917I and L920F mutations in 91.6, 4.2 and 4.2% of human head lice samples, respectively [ 50 ].…”