Quantitative structure-insecticidal activity of essential oils on the human head louse (Pediculus humanus capitis)

In the search for natural and non-toxic products alternatives to synthetic pesticides, the fumigant and repellent activities of 35 essential oils are predicted in the human head louse (Pediculus humanus capitis) through the Quantitative Structure-Activity Relationships (QSAR) theory. The number of constituents of essential oils with weight percentage composition greater than 1% varies from 1 to 15, encompassing up to 213 structurally diverse compounds in the entire dataset. The 27,976 structural descriptors used to characterizing these complex mixtures are calculated as linear combinations of non-conformational descriptors for the components. This approach is considered simple enough to evaluate the effects that changes in the composition of each component could have on the studied bioactivities. The best linear regression models found, obtained through the Replacement Method variable subset selection method, are applied to predict 13 essential oils from a previous study with unknown property data. The results show that the simple methodology applied here could be useful for predicting properties of interest in complex mixtures such as essential oils.

COVID-19 pandemic and the consumption of self-care products for pediculosis capitis in Portugal: an interrupted time-series analysis

This study aims to assess the effect of the COVID-19 pandemic on the consumption of self-care products for pediculosis capitis management, in Portugal. A segmented regression analysis of interrupted time series (March 2020) was performed from January 2017 to August 2023 to analyze the short- and long-term impact of the COVID-19 pandemic on the consumption of pediculicides and related products. Monthly rates of absolute consumption were estimated by community pharmacies' dispensing records. Portuguese municipalities were organized into quintiles according to their purchasing power index and percentage of youth, to study the association of these social and demographic variables on the sale of these products. COVID-19 pandemic significantly reduced the sales of products indicated for pediculosis. Since the start of the pandemic, an absolute decrease of 21.0 thousand packages was observed in the monthly average consumption (p < 0.0001) compared to the pre-pandemic period. After this reduction, the average monthly trend increased in the pandemic period in comparison with the previous period, although not significant (267.0 packages per month, p = 0.1102). Regions with higher disposable income and more young people were associated with higher sales of these products. The outbreak of the COVID-19 pandemic has had a notable impact on the sales of self-care products for pediculosis capitis in Portugal, in the short term. The lockdowns and other isolation measures implemented to control the spread of the virus may have led to a decrease in the number of head lice cases, consequently resulting in a reduction in sales of products.

Internet searching on the head louse in the UK since the COVID-19 pandemic

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.

Head louse infestations before and during the COVID-19 epidemic in Israel

Head louse infestations caused by Pediculus humanus capitis (Phthiraptera: Pediculidae) are a public health problem in developing and developed countries worldwide. Head to head contact is by far the most common mode of lice transmission. In March 2020, WHO declared the COVID-19 outbreak as a pandemic. Starting from March 2020, the Israeli government established mandatory isolation for extensive periods including closure of school systems for very long time. The aim of the project was to compare the pediculicide sale numbers before the COVID-19 epidemic with those starting of the epidemic in 2020, as a possible marker for changing epidemiology of head lice during the COVID pandemic. Data were collected from a large pharmacy chain in Israel, which provided the actual sales of pediculicides during the years 2010-2020. During the period 2010-2019 a significant increase of pediculicide sales from 281,986 - 498,107 was observed, the highest number being from 2019. In 2020, this number dropped to 294,477, a significant drop compared to previous years and to 2019. The results of this study suggest that head louse infestations are increasing in the last years, while the extended isolation of children due to COVID-19 influenced significantly the infestation rate of children with head lice.

Immune mechanisms in human Sarcoptes scabiei (Acari: Sarcoptidae) infestations

Scabies is a parasitic infestation of human and animal skin caused by different strains of the itch mite, Sarcoptes scabiei. The World Health Organization (WHO) has declared scabies in human as a neglected tropical disease, and today over 200 million people worldwide are affected. The two most commonly reported clinical manifestation of the condition are ordinary (OS) and crusted scabies (CS). CS, which can lead to fatal consequences due to secondary bacterial infections, is mostly observed in immunocompromised subjects but can also, although rarely, be detected in immunocompetent individuals. Innate and adaptive immune system components are involved in protection and pathogenesis of scabies, although with some differences between OS and CS. While the cutaneous immune response is dominated by CD4⁺ T-cells in OS, it is mainly mediated by CD8⁺ T-cells in CS. The two clinical conditions also differ in CD4⁺ T-cell-mediated immune responses with mixed T_H 1/T_H 2 (protective) and T_H 2/T_H 17 (non-protective) immunoprofiles in OS and CS, respectively. Moreover, the development of CS is associated with early immunosuppression that is followed by deleterious immune response to uncontrolled mite proliferation. However, the immune response to scabies still needs further attention due to inconsistent results in the literature. The aim of this study is to attract more attention to this area by summarizing the current literature on innate and adaptive immune responses triggered against S. scabiei mites.

Head lice were also affected by COVID-19: a decrease on Pediculosis infestation during lockdown in Buenos Aires

Pediculosis is a worldwide disease affecting school-aged children produced by the presence of the head louse, Pediculus humanus capitis De Geer, an obligate ectoparasite on the human scalp feeding exclusively on blood. Transmission occurs primarily through direct physical head-to-head contact. In March 2020, the World Health Organization (WHO) declared the COVID-19 outbreak as a pandemic. COVID-19 is caused by SARS-CoV-2, a variant of the coronavirus. Therefore, on March 18, 2020, the Argentinean government established mandatory isolation for an indefinite period. This obligatory isolation interrupted regular classes avoiding direct contact between children, thus affecting the dispersal route of individuals and the evolution of head louse populations. In this study, we evaluated through an online survey how confinement affected the prevalence of lice during lockdown compared to the situation prior to confinement. The survey allowed to discriminate the different control strategies, the number of treatments, and the amount of insects recorded by parents. Data of 1118 children obtained from 627 surveys were analyzed. As the main result, it was observed that prevalence of lice decreased significantly from before (69.6%) to during (43.9%) COVID-19 lockdown. Moreover, head lice infestation was more effectively controlled in households with up to 2 children in comparison to households with 3 or more children. This is the first study that analyzed the prevalence of head lice during COVID-19 pandemic. In addition, this work demonstrated the impact of social distance in the population dynamics of head lice and how it could affect the control strategies in the future.

Investigation of the prevalence of Head Lice and Factors Affecting Them in Infected People Referring to Gerash County Health Center

Background and aims: Pediculosis is one of the most common parasitic diseases that affect a wide range of age groups. The prevention of head lice infections promotes the physical and mental health of people in the community. Thus, the aim of this study was to investigate the prevalence of head lice infections and the factors affecting them in those who referred to health centers in Gerash County from 2011 to 2018. Methods: This descriptive cross-sectional study was conducted on patients suspected with head lice infections in health centers in Gerash. These infections were diagnosed by observing adult lice, nymphs, or nits on the head with the help of a magnifying glass. The collected data were then analyzed using SPSS software, version 22 and P˂ 0.05 was considered as the significance level. Results: In general, 66410 patients suspected with head lice were examined, of whom 2,547 cases (3.83%) were reported with confirmed infections including 2395 female (94.03%) and 152 male (5.97%) cases. The highest levels of infections were reported in the age group of 6-10 years while the lowest levels of infections were found in children less than 6 years of age. A significant statistical relationship was observed between head lice and gender, age, season, and the place of residence, and year of infection (P<0.05). Conclusion: Due to the increasing trend of head lice infections in recent years, pediculosis is still considered a health problem. Therefore, training on personal hygiene, adequate access to health services, and early diagnosis and treatment can play an important role in the prevention and elimination of head lice.

Knowledge, Attitude, and Practice of Pediculus Capitis Prevention and Control and Their Predictors among Schoolchildren in Woreta Town, Northwest Ethiopia, 2018: A School-Based Cross-Sectional Study

Background

Pediculus capitis is a human head lice infestation, a major public health issue that is most prevalent in resource-limited countries globally. The current study aimed to assess the knowledge, attitude, and practice of pediculus capitis prevention and control and their predictors among schoolchildren in North West Ethiopia.

Methods

About 402 randomly selected schoolchildren from three schools in Woreta town participated in the study from April to June 2018. The outcomes of this study were knowledge, attitude, and self-reported practice of schoolchildren about pediculus capitis prevention and control. We used EPI Info 7.1 and SPSS 21 software for data entry and analysis, respectively. Binary logistic regression was employed to test the association of covariates with the outcome/response variables. Variables with a p value <0.2 during the bivariable binary logistic regression analysis were included in the multivariable binary logistic regression analysis. Variables with p value <0.05 were declared as significantly associated with outcomes.

Results

The mean age of the study participants was 10.19 (±1.62) years. About 58.8%, 45.8%, and 78.6% of the schoolchildren had better self-reported pediculus capitis prevention knowledge, attitude, and practice, respectively. Age of children [9 to 11 years (AOR = 2.24, 95% C.I (1.10, 4.55)) and>12 years (AOR = 3.84, 95% C.I (1.56, 9.46))], better practice (AOR = 2.93, 95% C.I (1.39, 6.18)), and those who were not infested (AOR = 2.25, 95% C.I (1.14, 4.44)) were predictors of knowledge regarding pediculus capitis prevention. Better practice (AOR = 4.33, 95% C.I (1.69, 11.09)) and absence of infestation (AOR = 2.97, 95% C.I (1.64, 5.36)) were predictors of attitude of schoolchildren about pediculus capitis prevention. Number of students in a class [51 to 56 students per classroom, AOR = 4.61, 95% C.I (1.83, 11.67); 57 to 58 students per classroom, AOR = 8.18, 95% C.I (2.73, 24.46)], less than five family size (AOR = 2.37, 95% C.I (1.24, 4.54)), better knowledge (AOR = 2.93, 95% C.I (1.32, 6.50)), desirable attitude (AOR = 4.24, 95% C.I (1.60, 11.23)), and absence of infestation (AOR = 3.52, 95% C.I (1.22, 10.15)) were predictors of self-reported pediculus capitis prevention practice.

Conclusion

The knowledge, attitude, and practice of schoolchildren regarding pediculus capitis prevention and control were not satisfactory. To bring change, intensive efforts on factors associated with the knowledge, attitude, and practice should be encouraged.

First evidence of the mutations associated with pyrethroid resistance in head lice (Phthiraptera: Pediculidae) from Honduras

Background

The human head louse, Pediculus humanus capitis, is a cosmopolitan blood-sucking ectoparasite affecting mostly schoolchildren in both developed and developing countries. In Honduras, chemical pediculicides are the first line of treatment, with permethrin as their main active ingredient. Despite the extended use of these products, there is currently no research investigating insecticide resistance in Honduran head lice. In head lice, the most common mechanism is knockdown resistance (kdr), which is the result of two point mutations and the associated amino acid substitutions, T917I and L920F, within the voltage-sensitive sodium channel (VSSC).

Methods

Genomic DNA was extracted from 83 head lice collected in the localities of San Buenaventura and La Hicaca, Honduras. Polymerase chain reaction (PCR) was used to amplify a 332-bp fragment of the VSSC gene that contains a site affected by C/T mutation which results in a T917I amino acid substitution on each human head louse genomic DNA fragments.

Results

The C/T non-synonymous mutation which results in the T917I kdr amino acid substitution was detected in both head lice populations at frequencies ranging between 0.45–0.5. Globally, the frequency of this substitution was 0.47. Of these, 5 (6.1%) were homozygous susceptible and 78 (93.9%) were heterozygotes. The kdr-resistant homozygote (RR) was not detected in the studied populations. Thus, 93.9% of the head lice collected in Honduras harbored only one T917I allele. Exact test for the Hardy-Weinberg equilibrium for both localities showed that genotype frequencies differed significantly from expectation. In addition, San Buenaventura and La Hicaca populations had an inbreeding coefficient (F_is) < 0, suggesting an excess of heterozygotes.

Conclusions

To our knowledge, this is the first study showing the presence of the C/T mutation responsible of the T917I kdr allele associated with pyrethroid resistance in P. h. capitis from Honduras. The PCR-restriction fragment length polymorphism (RFLP) employed here has demonstrated to be a reliable, economic, and reproducible assay that can be used to accurately genotype individual head lice for the mutation encoding the resistance-conferring T917I amino acid substitution. This highlights the necessity of proactive resistance management programmes designed to detect pyrethroid mutations before they become established within populations of head lice.

First Determination of Pyrethroid Knockdown Resistance Alleles in Human Head Lice (Phthiraptera: Pediculidae) From Chile

The infestation with the human ectoparasite, Pediculus humanus capitis (De Geer), is a common public health problem affecting schoolchildren worldwide. In Chile, the main active ingredients present in the over-the-counter pediculicides contain pyrethroids. Despite the extended use of these products, there is no evidence of the insecticide resistance status of the head lice geographically located in Chile. The most extended resistant mechanism of pyrethroids consists of the target site insensitivity (Kdr) determined by the presence of mutations linked to insecticide-binding sites in the voltage-sensitive sodium channel. T917I is recognized as the main mutation in head lice, and detection is considered to be a biomarker of resistance. The goal of the present study was to detect the presence and distribution of T917I mutation in five geographic locations of Chile. All five geographically selected louse populations had a frequency of pyrethroid resistance genes that ranged from 36 to 77%, and 94.9% of the collected head lice had one or two T917I mutant alleles. Moreover, the frequency of the aggregate resistant alleles was 50.5%. This is the first evidence that head lice in Chile had the mutations commonly associated with the resistance to pyrethroids. Moreover, the overrepresentation of heterozygotes in the studied populations suggests that head lice in Chile are currently under active selective pressure.

Scabies and risk of skin sores in remote Australian Aboriginal communities: A self-controlled case series study

Background

Skin sores caused by Group A streptococcus (GAS) infection are a major public health problem in remote Aboriginal communities. Skin sores are often associated with scabies, which is evident in scabies intervention programs where a significant reduction of skin sores is seen after focusing solely on scabies control. Our study quantifies the strength of association between skin sores and scabies among Aboriginal children from the East Arnhem region in the Northern Territory.

Methods and results

Pre-existing datasets from three published studies, which were conducted as part of the East Arnhem Healthy Skin Project (EAHSP), were analysed. Aboriginal children were followed from birth up to 4.5 years of age. Self-controlled case series design was used to determine the risks, within individuals, of developing skin sores when infected with scabies versus when there was no scabies infection. Participants were 11.9 times more likely to develop skin sores when infected with scabies compared with times when no scabies infection was evident (Incidence Rate Ratio (IRR) 11.9; 95% CI 10.3–13.7; p<0.001), and this was similar across the five Aboriginal communities. Children had lower risk of developing skin sores at age ≤1 year compared to at age >1 year (IRR 0.8; 95% CI 0.7–0.9).

Conclusion

The association between scabies and skin sores is highly significant and indicates a causal relationship. The public health importance of scabies in northern Australia is underappreciated and a concerted approach is required to recognise and eliminate scabies as an important precursor of skin sores.

Skin sores, also known as impetigo, are highly contagious bacterial skin infections, which are found commonly in school children and occasionally in adults. Skin sores are prevalent in disadvantaged or resource-poor settings. In Australia, about two thirds of Aboriginal children suffer from skin sores by their first birthday. If untreated or treated poorly, skin sores can eventually cause heart and kidney problems. It is also believed that scabies, another common skin infection in Aboriginal children, can increase the risk of developing skin sores by allowing the bacteria to enter the skin more easily through breaks in the skin. Our research explored the following: if scabies is a risk factor for skin sores then what is the strength of the association between the two conditions.

Response of Pediculus humanus capitis (Phthiraptera: Pediculidae) to Volatiles of Whole and Individual Components of the Human Scalp

The head louse Pediculus humanus capitis (De Geer) (Phthiraptera: Pediculidae) is a cosmopolitan human ectoparasite causing pediculosis, one of the most common arthropod parasitic conditions of humans. The mechanisms and/or chemicals involved in host environment recognition by head lice are still unknown. In this study, we evaluated the response of head lice to volatiles that emanate from the human scalp. In addition, we identified the volatile components of the odor and evaluated the attractive or repellent activity of their pure main components. The volatiles were collected by means of Solid Phase microextraction and the extract obtained was chemically analyzed by gas chromatograph-mass spectrometer. Twenty-four volatile were identified in the human scalp odor, with the main compounds being the following: nonanal, sulcatone, geranylacetone, and palmitic acid. Head lice were highly attracted by the blend human scalp volatiles, as well as by the individual major components. A significant finding of our study was to demonstrate that nonanal activity depends on the mass of the compound as it is repellent at high concentrations and an attractant at low concentrations. The results of this study indicate that head lice may use chemical signals in addition to other mechanisms to remain on the host.

Cytogenetic Features of Human Head and Body Lice (Phthiraptera: Pediculidae)

The genus Pediculus L. that parasitize humans comprise two subspecies: the head lice Pediculus humanus capitis De Geer and the body lice Pediculus humanus humanus De Geer. Despite the 200 yr of the first description of these two species, there is still a long debate about their taxonomic status. Some authors proposed that these organisms are separate species, conspecifics, or grouped in clades. The sequencing of both forms indicated that the difference between them is one gene absent in the head louse. However, their chromosomal number remains to be determined. In this study, we described the male and female karyotypes, and male meiosis of head and body lice, and examined the chromatin structure by means of C-banding. In P. h. humanus and P. h. capitis, the diploid chromosome complement was 2 n = 12 in both sexes. In oogonial prometaphase and metaphase and spermatogonial metaphase, it is evident that chromosomes lack of a primary constriction. No identifiable sex chromosomes or B chromosomes were observed in head and body lice. Neither chiasmata nor chromatin connections between homologous chromosomes were detected in male meiosis. The meiotic behaviour of the chromosomes showed that they are holokinetic. C-banding revealed the absence of constitutive heterochromatin. Our results provide relevant information to be used in mapping studies of genes associated with sex determination and environmental sensing and response.

Influence of the formulations in removing eggs of Pediculus humanus capitis (Phthiraptera: Pediculidae)

Head lice lay eggs in human head hairs in order to reproduce. There is a difficulty associated to the process of detaching these eggs: they are tightly gripped to the hair by a secretion produced by female head lice. The physical removal of eggs has become an important part of treatment of louse infestations. The finding of new products to loosen the eggs is necessary to avoid mistaken diagnosis or reinfestations. This work aimed to compare different kinds of pediculicide formulations in order to find if their presentations represented differences in the egg remover effect. We also wanted to present a new device to test the efficacy of the egg remover formulations. Products with creamy presentations (Bio infant lice and egg remover and hair conditioner) and one containing dimethicone (Nyda) showed the lower mean forces compared with the control (lower mean forces represented best removal activity). Whereas, the Biferdil egg remover (gel) and Nopucid Tribit (hydroalcoholic lotion) had no egg removal effect, presenting the highest mean forces (177.82 and 189.99 mN, respectively) compared with the control. Additionally, we proposed a removal index (RI) to compare the efficacy of different products on the egg removal activity (RI > 0, good performance). The higher index values were for Bio infant lice and egg remover (0.72) and Biferdil hair conditioner (0.58). The lowest index values were for Biferdil egg remover (-0.26) and Nopucid Tribit (-0.35).The formulation of over the counter pediculicides in the egg remover effect was discussed.

Socioeconomic status, family background and other key factors influence the management of head lice in Norway

How head lice infestations are managed by households is an important but generally neglected issue in head lice research. In the present study, we investigate actions taken against head lice by Norwegian households in association with socioeconomic status, family background, school-related variables and other key factors. Repeat questionnaires distributed to caretakers of the same elementary school children during a 2-year period enabled us to study both previous head lice management and any changes in this management through time. Households from 12 schools spanning the main socioeconomic variation found in Norway participated in the study. All students with active head lice infestation were treated in the four investigated periods. Most caretakers used a thorough head lice checking technique and informed others of own infestation. Checking frequency was low as most children were inspected less than monthly. The best determinant of increased checking frequency and thoroughness was personal experience with head lice. The increased awareness, however, seemed to be somewhat short-lived, as there was a decrease in checking frequency and thoroughness within 1 year after infestation. Personal experience with head lice also increased general knowledge related to the parasite. Parents born in developing countries checked their children for head lice more frequently, although less thoroughly, informed fewer contacts when infested, used pediculicides preventively more often and knew less about head lice than parents born in developed countries. Households with highly educated mothers had a lower checking frequency, but their knowledge and willingness to inform others was high. Single parents were more concerned about economic costs and kept children home from school longer while infested than other parents. As head lice management varied among socioeconomic groups and with parental background, differentiated advice should be considered in the control of head lice. The biannual focus on head lice during the 2 years of investigation increased checking thoroughness, while checking frequency remained unchanged. Based on the results, we suggest new head lice management guidelines for health authorities.

Geographical distribution of pyrethroid resistance allele frequency in head lice (Phthiraptera: Pediculidae) from Argentina

The human head louse, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae), is an obligate ectoparasite that causes pediculosis capitis and has parasitized humans since the beginning of humankind. Head louse infestations are widespread throughout the world and have been increasing since the early 1990s partially because of ineffective pediculicides. In Argentina, the overuse of products containing pyrethroids has led to the development of resistant louse populations. Pyrethroid insecticides act on the nervous system affecting voltage-sensitive sodium channels. Three point mutations at the corresponding amino acid sequence positions M815I, T917I, and L920F in the voltage-gated sodium channel gene are responsible for contributing to knockdown resistance (kdr). The management of pyrethroid resistance requires either early detection or the characterization of the mechanisms involved in head louse populations. In the current study, we estimated the distribution of kdr alleles in 154 head lice from six geographical regions of Argentina. Pyrethroid resistance kdr alleles were found in high frequencies ranging from 67 to 100%. Of these, 131 (85.1%) were homozygous resistant, 13 (8.4%) were homozygous susceptible, and 10 (6.5%) were heterozygous. Exact tests for the Hardy-Weinberg equilibrium for each location showed that genotype frequencies differed significantly from expectation in four of the six sites studied. These results show that pyrethroid resistance is well established reaching an overall frequency of 88%, thus close to fixation. With 30 yr of pyrethroid-based pediculicides use in Argentina, kdr resistance has evolved rapidly among these head louse populations.

International guidelines for clinical trials with pediculicides

Pediculosis capitis, infestation with head lice, is common in all human societies. Chemical pediculicides are often used to control head louse infestations, particularly in wealthy communities. A significant number of different protocols have been used to test the efficacy and safety of pediculicides in clinical trials; this constrains scientific comparison of the evidence for efficacy of the different pediculicides. Here we recommend protocols for clinical trials of the efficacy and safety of single-, two-, and three-treatment interventions.

Detection of living Sarcoptes scabiei larvae by reflectance mode confocal microscopy in the skin of a patient with crusted scabies

Scabies is an intensely pruritic disorder induced by a delayed type hypersensitivity reaction to infestation of the skin by the mite Sarcoptes scabiei. The diagnosis of scabies is established clinically and confirmed by identifying mites or eggs by microscopic examination of scrapings from the skin or by surface microscopy using a dermatoscope. Reflectance-mode confocal microscopy is a novel technique used for noninvasive imaging of skin structures and lesions at a resolution compatible to that of conventional histology. Recently, the technique was employed for the confirmation of the clinical diagnosis of scabies.We demonstrate the first ever documentation of a larva moving freely inside the skin of a patient infected with scabies.

Ovicidal response of NYDA formulations on the human head louse (Anoplura: Pediculidae) using a hair tuft bioassay

Using the in vitro rearing system in conjunction with the hair tuft bioassay, NYDA and NYDA without fragrances formulations (92% wt:wt dimeticones) were 100% ovicidal (0% of treated eggs hatched) after an 8-h exposure of the eggs of the human head louse (Pediculus humanus capitis De Geer) following the manufacturer's instructions. Comparatively, 78 and 66% of eggs similarly exposed hatched after distilled deionized water or Nix (1% permethrin) treatments, respectively. NYDA and NYDA without fragrances formulations were also statistically and substantially more ovicidal than either distilled deionized water or Nix treatments after 10, 30 min, and 1 h exposures. Only the 10 min exposure of eggs to NYDA and NYDA without fragrances formulations resulted in hatched lice that survived to adulthood (5-8% survival). Of the lice that hatched from eggs exposed to NYDA formulations for 10 min, there were no significant differences in the time it took them to become adults, female fecundity or the viability of eggs laid by surviving females. The longevity of adults, however, was reduced after the 10 min treatments of eggs with NYDA and NYDA without fragrances formulations compared with either the distilled deionized water or Nix treatments.

Head lice prevalence among households in Norway: importance of spatial variables and individual and household characteristics

Head lice prevalence varies greatly between and within countries, and more knowledge is needed to approach causes of this variation. In the present study, we investigated head lice prevalence among elementary school students and their households in relation to individual and household characteristics as well as spatial variables. The investigation included households from 5 geographically separated municipalities. Present infestations among household members as well as previous infestations in the household were reported in a questionnaire. In elementary school students prevalence was low (1·63%), but more than one-third of the households (36·43%) had previously experienced pediculosis. Prevalence was higher in elementary school students than in other household members, and highest in third-grade children. Prevalence was also influenced by the school attended, which suggested that interactions between children in the same school are important for head lice transmission. Previous occurrence of head lice in homes also increased the risk of present infestation. Prevalence of previous infestations was higher in households with more children and in more densely populated municipalities, indicating that the density of hosts or groups of hosts influences transmission rates. These results demonstrate that information of hosts' spatial distribution as well as household and individual characteristics is needed to better understand head lice population dynamics.

Bioactivity of Argentinean essential oils against permethrin-resistant head lice, Pediculus humanus capitis

Infestation with the head louse, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae), is one of the most common parasitic infestation of humans worldwide. Traditionally, the main treatment for control of head lice is chemical control that is based in a wide variety of neurotoxic synthetic insecticides. The repeated overuse of these products has resulted in the selection of resistant populations of head lice. Thus, plant-derived insecticides, such as the essential oils seem to be good viable alternatives as some have low toxicity to mammals and are biodegradable. We determined the insecticidal activity of 25 essential oils belonging to several botanical families present in Argentina against permethrin-resistant head lice. Significant differences in fumigant activity against head lice were found among the essential oils from the native and exotic plant species. The most effective essential oils were Cinnamomum porphyrium, followed by Aloysia citriodora (chemotype 2) and Myrcianthes pseudomato, with KT(50) values of 1.12, 3.02 and 4.09; respectively. The results indicate that these essential oils are effective and could be incorporated into pediculicide formulations to control head lice infestations once proper formulation and toxicological tests are performed.

Efficacy of a grapefruit extract on head lice: a clinical trial

Twenty children aging 2-9 years old--four boys with short hair and 16 girls with long hair--were included in a clinical test on the efficacy of a product against head lice (Pediculus humanus capitis). Their hair were exposed to Licatack, which is a recently developed new anti-louse medicinal product containing extracts of grapefruits besides high quality shampoo components. Prior to this field trial, the product Licatack was tested dermatologically to be skin safe receiving the grade "very good". The children's mothers combed the kids prior to the start of the test in order to confirm that they were all lice-infested. The obtained lice were used for in vitro tests. All children were heavily infested. After combing and preservation of the living lice, the hair was wet with tap water. Then, 50 ml of the Licatack shampoo was placed onto the top of each child's head. Then, the mothers distributed the rather fluid product all over the hair thoroughly from their base at the skin until the free end. During this process, a type of massage, the product became foamy and it was easily recognized where the product covered the hair, thus, avoiding untreated spots. The hair of half of the treated children were washed with tap water after 10 min of exposition; while in the other half of the children, the exposition period was prolonged to 20 min before washing. When combing the kids with a metal louse comb after the washing, the lice were found immobile and they did not recover during the following observation period of 4 h. Only two lice from the group with an exposition time of only 10 min showed some slight leg movements after they had been combed off, but they died within the next 2 h. Thus, this new anti-louse medicinal product has a very quick and efficient activity besides its advantages of being non-inflammable, skin safe, and nice smelling. None of the kids claimed any burning at the skin or other side effects, although the skin showed, prior to treatment, lots of scars due to louse bites. The dead lice always appeared considerably shrunken due to drying. The second treatment after 10 days revealed a few dead larval stages since, apparently, some larvae (apparently treated at an early stage of development when treated) had hatched from the extremely numerous nits in the period between first and second treatment. Experiments with cutoff nits, however, showed that the product also kills larval stages inside nits.

Comparative in vitro tests on the efficacy and safety of 13 anti-head-lice products

Head lice are an emerging social problem, not only in economically poor countries but also in practically all other societies. Several of the common anti-louse products have lost--at least in part--their efficacy due to increasing resistance of lice against insecticides such as permethrin or allethrin. Other compounds, like lindan, were redrawn or banned due to high toxicity. Some recently developed products are based on dimethicones or cyclomethicones and turned out to be easily inflammable. Other styled medicinal products are based on plant extracts-some were proven of high efficacy-others of ineffectivity. The present study investigated in in vitro tests the anti-head louse efficacy of 13 products, the contents of which are used worldwide: Aesculo-Gel L, EtoPril, Goldgeist Forte, InfectoPedicul, Jacutin Pedicul Fluid, K.Laus, Liberalice, Licatack, Mosquito Läuse-Shampoo, Nyda, Paranix, Picksan Louse Stop, and Wash Away Louse. It turned out that several of them are easily inflammable, and therefore, they endanger users (InfectoPedicul, Paranix, EtoPril, Nyda, Goldgeist Forte, and K.Laus, see Table 1). Others have to remain for many hours on the hair in order to reach efficacy (Table 4). During such long periods, highly dosed oils may become inhaled and thus may become dangerous for the user's lung epithelia by covering them. When incubating the lice for 3 or 10 min in vitro, only the following products killed all lice exposed to these products: InfectoPedicul, Paranix, Jacutin Pedicul Fluid, Nyda, K.Laus, Picksan Louse Stop, Licatack, and Wash Away Louse. When evaluating the possible dangers for the users, the last three products, especially, derived from plant extracts, are safe and highly effective at the same time. Furthermore, they had been tested dermatologically as "very good".