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Abstract Background Head louse females secrete liquid gel, which is mainly composed of the louse nit sheath protein 1 (LNSP1) and LNSP2, when they lay eggs. The gel is crosslinked by transglutaminase (TG) to form the nit sheath, which covers most of the egg except the top operculum area where breathing holes are located. Knowledge on the selective mechanism of nit sheath solidification to avoid uncontrolled crosslinking could lead to designing a novel method of louse control, but no information is available yet. Methods To elucidate the crosslinking mechanisms of nit sheath gel inside the reproductive system of head louse females, in situ hybridization in conjunction with microscopic observation of the oviposition process was conducted. Results Histochemical analysis revealed that LNSP1 and LNSP2 are expressed over the entire area of the accessory gland and uterus, whereas TG expression site is confined to a highly localized area around the opening of posterior oviduct. Detailed microscopic observations of oviposition process uncovered that a mature egg is positioned in the uterus after ovulation. Once aligned inside the uterus, the mature egg is redirected so that its operculum side is tightly held by the ventral end of the uterus being positioned toward the head again and its pointed bottom end being positioned toward the dorsal end of the uterus, which functions as a reservoir for the nit sheath gel. Conclusions Physical separation of the TG-mediated crosslinking site from the ventral end of the uterus is necessary to avoid uncontrolled crosslinking inside the uterus and to ensure selective crosslinking over only the lower part of egg without any unwanted crosslinking over the operculum during oviposition. Graphical Abstract

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

Background: Head louse females secrete liquid gel, which is mainly composed of the louse nit sheath protein 1 (LNSP1) and LNSP2, when they lay eggs. The gel is crosslinked by transglutaminase (TG) to form the nit sheath, which covers most of the egg except the top operculum area where breathing holes are located. Knowledge on the selective mechanism of nit sheath solidification to avoid uncontrolled crosslinking could lead to designing a novel method of louse control, but no information is available yet. Methods: To elucidate the crosslinking mechanisms of nit sheath gel inside the reproductive system of head louse females, in situ hybridization in conjunction with microscopic observation of the oviposition process was conducted. Results: Histochemical analysis revealed that LNSP1 and LNSP2 are expressed over the entire area of the accessory gland and uterus, whereas TG expression site is confined to a highly localized area around the opening of posterior oviduct. Detailed microscopic observations of oviposition process uncovered that a mature egg is positioned in the uterus after ovulation. Once aligned inside the uterus, the mature egg is redirected so that its operculum side is tightly held by the ventral end of the uterus being positioned toward the head again and its pointed bottom end being positioned toward the dorsal end of the uterus, which functions as a reservoir for the nit sheath gel. Conclusions: Physical separation of the TG-mediated crosslinking site from the ventral end of the uterus is necessary to avoid uncontrolled crosslinking inside the uterus and to ensure selective crosslinking over only the lower part of egg without any unwanted crosslinking over the operculum during oviposition. [ABSTRACT FROM AUTHOR]

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 efectiveness 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 efect of piperonyl butoxide (PBO) on this toxicity were assessed using bioassays. Fragments of voltage-sensitive sodium channels (vssc) and cytochrome b (cytb) genes were amplifed 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 efect on the efects 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 signifcant diference 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 efect 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. [ABSTRACT FROM AUTHOR]

Background: Wide‐ranging restrictions on social and educational activities were imposed in 2020 in response to the COVID‐19 pandemic. These likely influenced the population dynamics of the head louse. Close physical contact between human hosts is required for transmission of this ectoparasite. Method: Pre‐ and post‐pandemic internet interest in the head louse in the UK was compared using Google Trends data from March 2017 to March 2022 and modeling using the Meta Prophet package. The influence of school holidays and school attendance was also investigated. Results: There was a sharp decline in internet searching of the term "head louse" from March 2020 onwards coinciding with COVID‐19 restrictions, and a large difference between pre‐ and post‐pandemic search volumes. No influence of school holidays or attendance on internet searching on the head louse was found. Conclusion: The results suggest pandemic restrictions have had a large effect on head louse incidence. [ABSTRACT FROM AUTHOR]

Head louse infestations continue to be a concern of public health in most countries, including the most developed ones. The present recommendations are intended to inform and stress the role and impact of the different authorities, institutions, industry, and the public in the control of head lice in order to reduce the prevalence of this parasite. We encourage health authorities to pursue more effective methods to correctly identify such infestations, and evaluate existing and new pediculicides, medical devices, louse repellents, and louse- and nit-removal remedies. Pediculicides and medical devices must have verifiable claims in the instructions for use and should be tested periodically to document current levels of resistance by lice to the active ingredients and to the formulated products. Where the prevalence of lice is claimed to be epidemic, children should be periodically evaluated objectively to document the actual level of prevalence. Continuing education for health providers and the general population promises to correct misinformation regarding the biology, prevention, and management of lice. Parents should regularly inspect their children for head lice and treat as necessary. Health authorities are encouraged to eliminate policies and practices that rely upon school exclusion as a means to reduce incidence and prevalence, e.g., the 'no-nit' policy which lacks scientific justification, and are counterproductive to the health and welfare of children. [ABSTRACT FROM AUTHOR]

Abstract Background Head louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. Recently, two homologous proteins, named louse nit sheath protein (LNSP) 1 and LNSP 2, were identified as adhesive proteins but the precise mechanism of nit sheath solidification is unknown. Methods We determined the temporal transcriptome profiles of the head louse accessory glands plus oviduct, from which putative major structural proteins and those with functional importance were deduced. A series of RNA interference (RNAi) experiments and treatment of an inhibitor were conducted to elucidate the function and action mechanism of each component. Results By transcriptome profiling of genes expressed in the louse accessory glands plus uterus, the LNSP1 and LNSP2 along with two hypothetical proteins were confirmed to be the major structural proteins. In addition, several proteins with functional importance, including transglutaminase (TG), defensin 1 and defensin 2, were identified. When LNSP1 was knocked down via RNA interference, most eggs became nonviable via desiccation, suggesting its role in desiccation resistance. Knockdown of LNSP2, however, resulted in oviposition failure, which suggests that LNSP2 may serve as the basic platform to form the nit sheath and may have an additional function of lubrication. Knockdown of TG also impaired egg hatching, demonstrating its role in the cross-linking of nit sheath proteins. The role of TG in cross-linking was further confirmed by injecting or hair coating of GGsTop, a TG inhibitor. Conclusions Both LNSP1 and LNSP2 are essential for maintaining egg viability besides their function as glue. The TG-mediated cross-linking plays critical roles in water preservation that are essential for ensuring normal embryogenesis. TG-mediated cross-linking mechanism can be employed as a therapeutic target to control human louse eggs, and any topically applied TG inhibitors can be exploited as potential ovicidal agents. Graphical abstract

Human body and head lice are highly related haematophagous ectoparasites but only the body louse has been shown to transmit Bartonella quintana, the causative agent of trench fever. The mechanisms by which body lice became a vector for B. quintana, however, are poorly understood. Following oral challenge, green fluorescent protein-expressing B. quintana proliferated over 9 days postchallenge with the number of bacteria being significantly higher in whole body vs. head lice. The numbers of B. quintana detected in faeces from infected lice, however, were approximately the same in both lice. Nevertheless, the viability of B. quintana was significantly higher in body louse faeces. Comparison of immune responses in alimentary tract tissues revealed that basal transcription levels of peptidoglycan recognition protein and defensins were lower in body lice and the transcription of defensin 1 was up-regulated by oral challenge with wild-type B. quintana in head but not in body lice. In addition, the level of cytotoxic reactive oxygen species generated by epithelial cells was significantly lower in body lice. Although speculative at this time, the reduced immune response is consistent with the higher vector competence seen in body vs. head lice in terms of B. quintana infection.

Purpose: Pediculosis caused by human head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae) is a public health problem with a high prevalence, especially among children in school age. Different chemical pediculicides (insecticides) are used against lice but the repeated application of these pediculicides for the treatment of P. humanus capitis infestation in the past decades has resulted in the development of resistance. The plant essential oils have been used as alternative sources of lice treatment agents. Pediculicidal activity of the essential oils of three Origanum species (O. onites, O. majorana and O. minutiflorum) against P. humanus capitis adults was examined in this study. Methods: Essential oils from aerial parts of three Origanum species were obtained by hydrodistillation using a Clevenger-type apparatus. P. humanus capitis specimens used were obtained from infested children by combing method at primary schools. Adult lice were exposed to three dilutions (1%, 0.5% and 0.1% w/v) of tested oils for 5 min using the adult immersion test. Results: According to the results, all Origanum essential oils at 1% concentration have been shown to significantly decrease the rate of limb, bowel and abdomen movements, producing more than 90% mortality after 12 h. Conclusion: Our results indicated that Origanum essential oils can be used for the development of new pediculicides against head louse. [ABSTRACT FROM AUTHOR]

Background: Head louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. Recently, two homologous proteins, named louse nit sheath protein (LNSP) 1 and LNSP 2, were identified as adhesive proteins but the precise mechanism of nit sheath solidification is unknown. Methods: We determined the temporal transcriptome profiles of the head louse accessory glands plus oviduct, from which putative major structural proteins and those with functional importance were deduced. A series of RNA interference (RNAi) experiments and treatment of an inhibitor were conducted to elucidate the function and action mechanism of each component. Results: By transcriptome profiling of genes expressed in the louse accessory glands plus uterus, the LNSP1 and LNSP2 along with two hypothetical proteins were confirmed to be the major structural proteins. In addition, several proteins with functional importance, including transglutaminase (TG), defensin 1 and defensin 2, were identified. When LNSP1 was knocked down via RNA interference, most eggs became nonviable via desiccation, suggesting its role in desiccation resistance. Knockdown of LNSP2, however, resulted in oviposition failure, which suggests that LNSP2 may serve as the basic platform to form the nit sheath and may have an additional function of lubrication. Knockdown of TG also impaired egg hatching, demonstrating its role in the cross-linking of nit sheath proteins. The role of TG in cross-linking was further confirmed by injecting or hair coating of GGsTop, a TG inhibitor. Conclusions: Both LNSP1 and LNSP2 are essential for maintaining egg viability besides their function as glue. The TG-mediated cross-linking plays critical roles in water preservation that are essential for ensuring normal embryogenesis. TG-mediated cross-linking mechanism can be employed as a therapeutic target to control human louse eggs, and any topically applied TG inhibitors can be exploited as potential ovicidal agents. [ABSTRACT FROM AUTHOR]

Body and head lice are known to be exclusive ectoparasites of human hosts. Current genomic and transcriptomic data suggest that both louse types represent ecotypes of the same species. They exhibit morphological and physiological differences that probably arose from living in different biotopes. Sensory traits represent suitable candidates to be affected by environmental heterogeneity. Therefore, through scanning electron microscope studies, this study analysed and compared the sensory structures of both ecotypes' antennae. Seven types of sensory structures were identified in both ecotypes: bristles, tuft organs, pore organs, single pore and three morphotypes of sensilla basiconica. Notably, the single pore and the morphotypes of sensilla basiconica were described for the first time in the body louse antenna. This study's comparative analysis mainly revealed size differences across the sensory structures of the ecotypes. Bristles of the flagellomere 2 of the body louse antenna were longer than the head louse bristles. In addition, the pore organs of the head louse antenna presented a higher diameter than those of the body louse. The possible relevance of size differences regarding the biotopes exploited by the body louse and the head louse is discussed. Yet, physiological studies may help to fully understand the phenotypical differences of both ecotypes. [ABSTRACT FROM AUTHOR]

Background: The head louse infestation is a public health issue in the world especially, affecting most people who live in camps, school-aged children and their families. Head lice treatment has economic ramifications that often under calculated. The aim of this study was evaluation of economic burden associated with head louse infestation in Iran. Methods: In a cross-sectional study, 500,002 infestations were diagnosed among suspected head lice infested people who referred to health care system in all provinces of Iran during 2017. Direct and indirect costs related to paid by patients and government systems were extracted by referring to accounting documents and interviews with patients and experts and were recorded in researcher-made forms. Microsoft Excel 2010 software was used for economic burden calculation. Results: The incidence rate of head lice infestation in Iran was 500,002/79,926,270 (625.5 per 100,000 populations). Economic burden of head lice in the country was calculated at 5,790,143$. Direct and indirect costs, governmental cost, out of pocket and total costs of head lice were included 3.14$, 2.84$, 5.98$, 5.60$ and 11.58$ per case respectively. Conclusion: The direct and indirect costs associated with treatment of infestations were relatively high. Therefore, the creation of medical facilities such as availability of diagnostic and treatment strategies can be effective in the control of infestation. The adoption of infestation prevention methods, such as health education to people at risk of infestation, reduces the incidence of head lice and imposition of related treatment costs on governmental health care system and head lice cases.

Human head lice and body lice (Pediculus humanus) are neglected ectoparasites. Head lice continue to be prevalent in children worldwide, and insecticide resistance in these insects has complicated their treatment. Meanwhile, body lice, which are most common in the developing world, are resurging among marginalized populations in developed nations. Today, the microbiome is being increasingly recognized as a key mediator of insect physiology. However, the microbial communities that inhabit human lice have remained unknown beyond only a few species of bacteria. Knowledge of the microbiomes of head and body lice could improve our understanding of the observed physiological differences between the 2 ecotypes and potentially inform the development of novel interventions against lice infestations and louse-borne infectious diseases. Toward these goals, here we performed 16S rRNA gene amplicon sequencing to characterize the microbiomes of both head and body lice and identify patterns of interest among these communities. Our data reveal that head and body lice harbor limited but distinct communities of bacteria that include known intracellular endosymbionts ("Candidatus Riesia pediculicola"), extracellular bacteria that may be horizontally acquired from the host environment, and a number of taxa of known or potential public health significance. Notably, in body lice, the relative abundance of vertically transmitted endosymbionts is lower than in head lice, which is a significant driver of greater alpha diversity. Further, several differentially abundant non-endosymbiont taxa and differences in beta diversity were observed between head lice and body lice. These findings support the hypothesis that microbiome differences could contribute to the divergence between human louse ecotypes and underscore the need for future studies to better comprehend the acquisition and physiological roles of human lice microbiomes. [ABSTRACT FROM AUTHOR]

Insect antennae are sophisticated sensory organs, usually covered with sensory structures responsible for the detection of relevant signals of different modalities coming from the environment. Despite the relevance of the head louse Pediculus humanus capitis as a human parasite, the role of its antennal sensory system in the highly dependent relation established with their hosts has been barely studied. In this work, we present a functional description of the antennae of these hematophagous insects by applying different approaches, including scanning electron microscopy (SEM), anterograde antennal fluorescent backfills, and behavioral experiments with intact or differentially antennectomized lice. Results constitute a first approach to identify and describe the head louse antennal sensilla and to determine the role of the antenna in host recognition. SEM images allowed us to identify a total of 35–40 sensilla belonging to seven different morphological types that according to their external architecture are candidates to bear mechano-, thermo-, hygro-, or chemo-receptor functions. The anterograde backfills revealed a direct neural pathway to the ipsilateral antennal lobe, which includes 8–10 glomerular-like diffuse structures. In the two-choice behavioral experiments, intact lice chose scalp chemicals and warm surfaces (i.e., 32°C) and avoided wet substrates. Behavioral preferences disappeared after ablation of the different flagellomeres of their antenna, allowing us to discuss about the location and function of the different identified sensilla. This is the first study that integrates morphological and behavioral aspects of the sensory machinery of head lice involved in host perception.

Head-lice infestation, pediculosis capitis, remains a public-health burden in many countries. The widely used first-line pediculicides and alternative treatments are often too costly for use in poor socio-economic settings. Ivermectin has been considered an alternate treatment for field practice. This study was composed of 2 parts, a cross-sectional survey and an intervention study. The main objectives were to determine the prevalence and potential factors associated with head-lice infestation, and to evaluate the effectiveness and safety of oral ivermectin administration. A community-based cross-sectional survey was conducted among 890 villagers in rural areas along Thai-Myanmar border. Females with infestations were eligible for the intervention study, and 181 participated in the intervention study. A post-treatment survey was conducted to assess acceptance of ivermectin as a treatment choice. Data analysis used descriptive statistics and a generalized- estimation-equation model adjusted for cluster effect. The study revealed the prevalence of head-lice infestation was 50% among females and only 3% among males. Age stratification showed a high prevalence among females aged <20 years, and among 50% of female school-children. The prevalence was persistent among those with a history of infestation. The major risk factors were residing in a setting with other infected cases, and sharing a hair comb. The study also confirmed that ivermectin was safe and effective for field-based practice. It was considered a preferable treatment option. In conclusion, behavior-change communication should be implemented to reduce the observed high prevalence of headlice infestation. Ivermectin may be an alternative choice for head-lice treatment, especially in remote areas. [ABSTRACT FROM AUTHOR]

Insect antennae are sophisticated sensory organs, usually covered with sensory structures responsible for the detection of relevant signals of different modalities coming from the environment. Despite the relevance of the head louse Pediculus humanus capitis as a human parasite, the role of its antennal sensory system in the highly dependent relation established with their hosts has been barely studied. In this work, we present a functional description of the antennae of these hematophagous insects by applying different approaches, including scanning electron microscopy (SEM), anterograde antennal fluorescent backfills, and behavioral experiments with intact or differentially antennectomized lice. Results constitute a first approach to identify and describe the head louse antennal sensilla and to determine the role of the antenna in host recognition. SEM images allowed us to identify a total of 35–40 sensilla belonging to seven different morphological types that according to their external architecture are candidates to bear mechano-, thermo-, hygro-, or chemo-receptor functions. The anterograde backfills revealed a direct neural pathway to the ipsilateral antennal lobe, which includes 8–10 glomerular-like diffuse structures. In the two-choice behavioral experiments, intact lice chose scalp chemicals and warm surfaces (i.e., 32°C) and avoided wet substrates. Behavioral preferences disappeared after ablation of the different flagellomeres of their antenna, allowing us to discuss about the location and function of the different identified sensilla. This is the first study that integrates morphological and behavioral aspects of the sensory machinery of head lice involved in host perception. [ABSTRACT FROM AUTHOR]

Head lice are considered as mandatory ectoparasites living on human head hair, which are transmitted to others through direct physical contact. This disease is mostly seen among children. In this review study, search was conducted among all studies performed in the past 20 years and studies were selected and reviewed. Contributing factors like location, study year, etc. were analyzed to procure a national management guideline. The finding of the present study showed that age, gender, parents' education, parents' job, family size, and presence of health inspector at schools were of statistical positive significance. However, hair type, hair length, dandruff, woven hair, and hair oil application showed no effect on head lice infestation. Head lice could be managed significantly regarding educational health and personal and public principles, especially regarding head lice biology and epidemiology to students, teachers, and parents.