Ovicidal and adulticidal activities of Cinnamomum zeylanicum bark essential oil compounds and related compounds against Pediculus humanus capitis (Anoplura: Pediculicidae)

The toxicity of cinnamon, Cinnamomum zeylanicum, bark essential oil compounds against eggs and adult females of human head louse, Pediculus humanus capitis, was examined using direct contact and vapour phase toxicity bioassays and compared with the lethal activity of their related compounds, benzyl alcohol, cinnamic acid, cinnamyl acetate, 4-hydroxybenzaldehyde and salicylaldehyde, as well as two widely used pediculicides, d-phenothrin and pyrethrum. In a filter-paper contact toxicity bioassay with female lice at 0.25 mg/cm², benzaldehyde was 29- and 27-fold more toxic than pyrethrum and d-phenothrin, respectively, as judged by median lethal time (LT₅₀) values. Salicylaldehyde was nine and eight times more active than pyrethrum and d-phenothrin, respectively. Pediculicidal activity of linalool was comparable with that of d-phenothrin and pyrethrum. Cinnamomum bark essential oil was slightly less effective than either d-phenothrin or pyrethrum. Benzyl alcohol and (E)-cinnamaldehyde exhibited moderate pediculicidal activity. After 24 h of exposure, no hatching was observed with 0.063 mg/cm² salicylaldehyde, 0.125 mg/cm² benzaldehyde, 0.5 mg/cm² Cinnamomum bark essential oil, 1.0 mg/cm² (E)-cinnamaldehyde, and 1.0 mg/cm² benzyl cinnamate. Little or no ovicidal activity was observed with d-phenothrin or pyrethrum. In vapour phase toxicity tests with female lice, benzaldehyde and salicylaldehyde were much more effective in closed containers than in open ones, indicating that the mode of delivery of these compounds was largely due to action in the vapour phase. Neither d-phenothrin nor pyrethrum exhibited fumigant toxicity. Cinnamomum bark essential oil and test compounds described merit further study as potential pediculicides or ovicides for the control of P. h. capitis.     

Susceptibility of British head lice, Pediculus capitis, to imidacloprid and fipronil

The head louse, Pediculus capitis De Geer (Phthiraptera: Pediculidae) has developed resistance to organochlorines, the organophosphate malathion and to pyrethroids in the U.K. Therefore, headlice from Bristol school children were bioassayed against two new insecticides, fipronil and imidacloprid. Pediculus capitis was fully susceptible to imidacloprid, but it required a relatively high dose and acted slowly. Fipronil acted faster at lower dose, but seemed to be affected by cross-resistance in a small proportion of P. capitis.     

Isoenzymes of human lice: pediculus humanus and P. capitis

Human lice (Phthiraptera: Pediculidae) from Africa, America and Europe were electrophoresed for 28 enzymes, with special interest in metabolic factors likely to be involved with insecticide resistance. Zymogram profiles of the body louse (Pediculus humanus L. from France and U.S.A.) and the head louse (P. capitis DeGeer from France, Madagascar, Mali & Senegal) were compared. Only esterase two enzymes, phosphoglucomutase (Pgm) and 3 (Est-3), showed electrophoretic variation. In our starch gel electrophoresis conditions, P. humanus showed three electromorphs of Pgm migrating anodally 6, 11 and 16 mm (designated alleles a, b, c, respectively). Of the putative Pgm alleles, b and c occurred in all samples of both species of lice, whereas allele a was found only in P. humanus lab strain from U.S.A. Esterase 3 had four electromorphs migrating 23, 26, 30 and 35 mm (designated alleles a, b, c and d). Among putative Est alleles, a was found only in P. capitis from Bamako (all 14 specimens aa homozygotes), allele d was found only in P. capitis from Dakar (39% frequency), whereas Est-3 alleles b and c showed apparently balanced polymorphism in all samples of both P. humanus and P. capitis except that from Bamako. Despite the limited amount of isoenzyme variation detected (only 2/31 polymorphic loci), divergences of Est-3 and Pgm among Pediculus populations may be relevant to their biosystematics and resistance.     

Engorgement response of human body lice Pediculus humanus (Insecta: Anoplura) to blood fractions and their components

ABSTRACT. Fed through a synthetic membrane, 80% of females of the human body louse, Pediculus humanus de Geer, engorged on whole human blood compared to 30% on platelet poor plasma. Both the plasma albumin and small molecular weight components of the cellular fraction seemed to stimulate engorgement by lice. Known haemo-phagostimulants such as adenosine triphosphate and diphosphoglyceric acid when added to plasma, did not replace the small molecular weight components of the cellular fraction as feeding stimuli. Nymphs discriminated less than adults in selecting blood fractions.     

In vitro efficacy of over-the-counter botanical pediculicides against the head louse Pediculus humanus var capitis based on a stringent standard for mortality assessment

Abstract.  Infestation of the head louse Pediculus humanus var capitis DeGeer (Phthiraptera: Pediculidae) is an important public health problem in Australia, with up to a third of children infested in some primary schools. Insecticide resistance and inadequate attention to the application instructions of topical pediculicides are common reasons for treatment failure. This study evaluated six popular Australian over-the-counter products against head lice, primarily comprised of different botanical extracts, and compared them with permethrin 1% (Quellada^®) and a non-treatment control in order to assess their in vitro efficacy. We also assessed commonly used criteria for evaluating pediculicide efficacy in vitro. All tested products failed to demonstrate high levels of efficacy with the exception of Tea Tree Gel^®, which outperformed 1% permethrin. Permethrin had a high level of efficacy, but using stringent criteria 18% of lice were not dead at 3 h, indicating some resistance to Quellada^®. Commonly used less stringent criteria were shown to overestimate mortality of head lice as a result of the protective phenomenon of stasis or sham death observed in exposed lice that may recover after some time. Using two different levels of stringency resulted in different rankings of efficacy for most products, with the exception of the first ranked product, Tea Tree Gel^®. Rankings of efficacy also varied over time, even within the different assessment criteria. Government regulatory agencies should require standard in vitro tests using stringent mortality criteria, with an observation period of ≥ 6 h, to determine the efficacy of new pediculicides, and only products that cause a minimum mortality rate (e.g. 80%) in head lice collected from the target population should be licensed for sale.     

The unusual reproductive system of head and body lice (Pediculus humanus)

Insect reproduction is extremely variable, but the implications of alternative genetic systems are often overlooked in studies on the evolution of insecticide resistance. Both ecotypes of Pediculus humanus (Phthiraptera: Pediculidae), the human head and body lice, are human ectoparasites, the control of which is challenged by the recent spread of resistance alleles. The present study conclusively establishes for the first time that both head and body lice reproduce through paternal genome elimination (PGE), an unusual genetic system in which males transmit only their maternally derived chromosomes. Here, we investigate inheritance patterns of parental genomes using a genotyping approach across families of both ecotypes and show that heterozygous males exclusively or preferentially pass on one allele only, whereas females transmit both in a Mendelian fashion. We do however observe occasional transmission of paternal chromosomes through males, representing the first known case of PGE in which whole‐genome meiotic drive is incomplete. Finally, we discuss the potential implications of this finding for the evolution of resistance and invite the development of new theoretical models of how this knowledge might contribute to increasing the success of pediculicide‐based management schemes.     

Prevalence of head lice (Pediculus humanus capitis) infestation among schools workers in the Eastern Region,Saudi Arabia

In a cross-sectional survey in February-May 2019, the prevalence of Pediculosis capitis with demographic data and the behavioral practices were investigated among 750 participants in the Eastern region of Saudi Arabia. Female participation was highly remarked with a percentage of 94.08% compared to that of male one about 5.91%. A deficiency of knowledge about lice infestation was noted especially among illiterate participants raised from their socio-economic levels (p-value = 0.001). Lice infestation reached higher rates in children aged less than 20 years with itching of the hair scalp. The obtained results revealed that 59.33% of the respondents believed that frequency of personal hygiene and washing of hair were the best methods for preventing the lice infestation. However, the treatment of lice infestation using anti-lice agents (p-value = 0.020) was preferred by 14.26% of participants. Although knowledge about the preventive tools for lice infestation (p-value 0.089) was not significantly associated with the experience of infestation but knowledge about the appropriate treatment to kill lice (p-value 0.020) and the wrong practices in the treatment of a head lice infestation were (p-value 0.005) significantly associated with the experience of infestation. Health programs and campaigns preventions are highly advised to increase the awareness of Pediculosis capitis with an effective strategic plan to control, manage, and prevent this disease.     

Determination,mechanism and monitoring of knockdown resistance in permethrin-resistant human head lice,Pediculus humanus capitis

Permethrin resistance has been reported worldwide and clinical failures to commercial pediculicides containing permethrin have likewise occurred. Permethrin resistance in head lice populations from the U.S. is widespread but is not yet uniform and the level of resistance is relatively low (～ 4–8 fold). Permethrin-resistant lice are cross-resistant to pyrethrins, PBO-synergized pyrethrins and to DDT. Nix^®, when applied to human hair tufts following manufacturer's instructions, did not provide 100% control when assessed by the hair tuft bioassay in conjunction with the in vitro rearing system. Resistance to permethrin is due to knockdown resistance (kdr), which is the result of three point mutations within the α-subunit gene of the voltage-gated sodium channel that causes amino acid substitutions, leading to nerve insensitivity.A three-tiered resistance monitoring system has been established based on molecular resistance detection techniques. Quantitative sequencing (QS) has been developed to predict the kdr allele frequency in head lice at a population level. The speed, simplicity and accuracy of QS made it an ideal candidate for a routine primary resistance monitoring tool to screen a large number of louse populations as an alternative to conventional bioassay. As a secondary monitoring method, real-time PASA (rtPASA) has been devised for a more precise determination of low resistance allele frequencies. To obtain more detailed information on resistance allele zygosity, as well as allele frequency, serial invasive signal amplification reaction (SISAR) has been developed as an individual genotyping method. Our approach of using three tiers of molecular resistance detection should facilitate large-scale routine resistance monitoring of permethrin resistance in head lice using field-collected samples.     

Partial characterization and post-feeding activity of midgut aminopeptidase in the human body louse, Pediculus humanus humanus

Abstract. A leucine aminopeptidase was found in the midgut of the human body louse, Pediculus humanus humanus L. (Anoplura: Pediculidae). The enzyme is activated by the bloodmeal with a pH optimum at 8. The enzyme is soluble in both aqueous and detergent-containing solutions. The two forms of the enzyme had the same Km but exhibited different catalytic activities with regard to Vmax values in these solutions. The enzyme is inhibited competitively by a substrate analogue 1,10-phenanthroline and by Mn²⁺ ions in the presence and absence of detergent.     

Development of a paw paw herbal shampoo for the removal of head lice

The development and clinical testing of an herbal lice removal shampoo, containing a standardized extract of paw paw, thymol, and tea tree oil, are described. All of these ingredients were selected for their ability to deplete adenosine triphosphate (ATP) levels and, thus, prevent ATP-dependent pesticide resistance. Optimum concentrations of the ingredients, treatment times, and dosing schedules were established through in vitro tests with head lice. In addition to pilot studies involving 21 participants, a final clinical trial, using the optimum shampoo formulation in 16 participants, demonstrated 100% effectiveness in removing head lice and nits.     

Partial purification of the aminopeptidase from the midgut of the human body louse, Pediculus humanus humanus

The midgut of the human body louse Pediculus humanus humanus contains a thermally stable leucine aminopeptidase, which was detected by agarose gel electrophoresis using l ‐amino oxidase. Midgut extracts were homogenized in saline or in 1% Triton X‐100 and the aminopeptidase was purified by Superose 6 gel filtration chromatography. A peak with enzyme activity that was extracted with or without Triton X‐100 was eluted at a molecular weight 67–69 kDa. Non‐denaturing polyacrylamide gel electrophoresis resolved one band of molecular weight of 69 kDa for samples that were extracted in a saline buffer. Two closely linked bands of molecular weight 67 kDa and 69 kDa were observed in samples that were extracted in 1% Triton X‐100.     

The geographical segregation of human lice preceded that of Pediculus humanus capitis and Pediculus humanus humanus

In order to investigate human-louse phylogeny, we partially sequenced two nuclear (18S rRNA and EF-1 alpha) and one mitochondrial (COI) genes from 155 Pediculus from different geographical origins. The phylogenetic analysis of 18S rRNA and EF-1 alpha sequences showed that human lice were classified into lice from Sub-Saharan Africa and lice from other areas. In both clusters, head and body lice were clearly grouped into two separate clusters. Our results indicate that the earliest divergence within human pediculidae occurred between African lice and other lice, and the divergence between head and body lice was not the result from a single event.     

DNA detection rates of host mtDNA in bloodmeals of human body lice (Pediculus humanus L., 1758)

Using polymerase chain reaction, we investigated the extent to which digestion affects the potential to amplify 12S mitochondrial DNA sequences from bloodmeals of individual human body lice (Pediculus humanus L.) (Phthiraptera, Pediculidae) up to 72 h after feeding on a surrogate rabbit host (Oryctolagus cuniculus L.) (Lagomorpha, Leporidae). Two rabbit-specific primer pairs were developed to produce amplicons of 199 bp and 283 bp, the smaller of which was found to have a significantly slower decay rate. Median detection periods (T50) for the amplicons were 20 h and 12 h, with maximum detection periods of 24 h and 12 h, respectively, suggesting an inversely proportional linear relationship between amplicon size and digestion time. The data provide an indication of timeframes essential for the design of forensic sampling protocols and a basis for investigating the feeding frequency of human lice.     

Effects of blood type and blood handling on feeding success,longevity and egg production in the body louse,Pediculus humanus humanus

The effects of feeding different types of human blood to human body lice, Pediculus humanus humanus L. (Phthiraptera: Pediculidae), on feeding success, longevity and numbers of eggs laid were investigated using an artificial blood‐feeding system in the laboratory. No significant differences were found between lice fed on different human blood types for any of the parameters tested. However, when lice were fed on human blood of one blood type followed immediately by a different blood type, they took significantly smaller bloodmeals, their longevity was reduced and they laid fewer eggs per female than control lice that had been fed twice on the same human blood type. When lice were fed human blood that had been stored for 1–26 weeks, the quantity of blood taken, the proportion of lice that became fully engorged and lice longevity diminished gradually as the storage time of the blood increased, but there was no effect of storage time on the mean number of eggs laid per female. However, lice would not feed on 26‐week‐old blood. The type of anticoagulant used had a significant effect on the proportion fed, longevity and number of eggs laid per female. Generally, EDTA (ethylenediaminetetraacetic acid)‐treated blood reduced longevity and the number of eggs laid per female to a greater degree than heparinized or citrated blood. Lice fed on rabbit blood took significantly larger amounts of blood, lived longer and laid a higher mean number of eggs per female than lice fed on human blood.     

Repellency of essential oils and their components to the human body louse, Pediculus humanus humanus

Five essential oils and nine of their components were compared to diethyl toluamide (DEET) for their repellent activity against the human body louse, Pediculus humanus humanus. The absolute or intrinsic repellency of the compounds was tested by applying the repellent to corduroy patches and comparing them with untreated patches. It was found that the most effective repellents were DEET and citronella, whose activity lasted at least 29 days. The activity of rosemary lasted at least 18 days and that of eucalyptus more than 8 days. The repellent activity of the oil components such as citronellal and geraniol lasted more than 15 and 8 days, respectively. DEET remained effective at a dilution of 1:32, geraniol at 1:8, citronella at 1:4 and rosemary and citronellal at 1:1. The comparative or standard repellency of the candidate repellents was examined with the aid of a new screening technique using hairs treated with ammonium bicarbonate which is attractive to lice. Using this technique it could be shown that the repellent activity of citronella and geraniol lasted 2 days and that of rosemary and citronellal for only one day. DEET was active for less than one day. Serial dilutions of these substances also revealed that citronella was the most potent repellent for lice, followed by citronellal, rosemary, geraniol and DEET. The differences however, were not significant.     

Geographic distributions and origins of human head lice (Pediculus humanus capitis) based on mitochondrial data

Human head lice (Pediculus humanus capitis) are subdivided into 3 deeply divergent mitochondrial clades (Clades A, B, and C), each having unique geographical distributions. Determining the evolutionary history and geographic distribution of these mitochondrial clades can elucidate the evolutionary history of the lice as well as their human hosts. Previous data suggest that lice belonging to mitochondrial Clade B may have originated in North America or Asia; however, geographic sampling and sample sizes have been limited. With newly collected lice, we calculate the relative frequency, geographic distribution, and genetic diversity of louse mitochondrial clades to determine the geographic origin of lice belonging to Clade B. In agreement with previous studies, genetic diversity data support a North American origin of Clade B lice. It is likely that lice belonging to this mitochondrial clade recently migrated to other geographic localities, e.g., Europe and Australia, and, if not already present, may disperse further to occupy all geographic regions.     

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

The head lice, Pediculus humanus capitis (Phthiraptera:Pediculidae), is an obligate ectoparasite of humans that causes pediculosis capitis, a nuisance for millions of people worldwide, with high prevalence in children. Pediculosis capitis has been treated by methods that include the physical remotion of lice, various domestic treatments and conventional insecticides. None of these methods render complete protection, and there is clear evidence for the evolution of resistance and cross-resistance to conventional insecticides. Non-toxic alternative options are hence needed for head lice treatment and/or prevention, and natural products from plants, especially essential oils (EOs), are good candidates for safer control agents that may provide good anti-lice activity and low levels of evolved resistance. A few EOs have been tested as repellents with promissory results, although often in vitro tests and clinical trials produce contradictory results. A handful of fixed extracts and several EOs and their individual components have also been tested as contact pediculicides or fumigants. The studies have focused mainly on plant families characterized for the production of EOs. While many EOs and individual compounds showed pediculicide activity, comparing results is difficult due to the diverse bioassay methodologies. Studies of anti-lice activity of individual EO components provide the basis for preliminary conclusions of structure–activity relationships, although no clear patterns can yet be drawn. We here attempt to provide a concise compilation of the available information on anti-lice activity of plant extracts and plant-derived compounds, which we hope may be of help for future developments in this area.

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Immunization of rabbits with faecal extract of Pediculus humanus, the human body louse: effects on louse development and reproduction

Abstract Immunization of rabbits with a faecal extract of the human body louse (Pediculus humanus) induced a high titre of specific IgG. The mean weight of Wood taken by females fed on the immunized rabbits was significantly lower (29%) than taken by females fed on the control rabbits. The mean number of eggs per female fed on the immunized rabbits was significantly lower than for females fed on the control rabbits. The hatchability of the eggs laid by lice fed on immunized rabbits (91%) was significantly lower than of those fed on control rabbits (94%). The rate of development of nymphs fed on control rabbits was significantly higher than those fed on the immunized rabbits. There was no difference in survival rates of lice fed on immunized and control rabbits.