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.     

Ovicidal and adulticidal effects of monoterpenoids against permethrin-resistant human head lice, Pediculus humanus capitis

Abstract.  The improper use of pediculicides containing permethrin has led to the development of resistance. Thus, new alternatives for control are needed. Plant-derived insecticides are attractive alternatives to common chemical insecticides because most of them are environmentally friendly and non-toxic to mammals. The toxic activity of 23 monoterpenoids belonging to several chemical classes was tested against the eggs of permethrin-resistant head lice, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae). Significant differences in ovicidal action were observed among the tested substances. The most effective chemicals were hydrocarbons and ethers, followed by ketones, alcohols, phenols and esters. A linear relationship between egg mortality and knockdown time (KT₅₀) on adults by the tested components revealed that most of the components were effective on both egg and adult stages. The monoterpenoids described herein are good candidates as effective pediculicides.     

Infestation of people with lice in Kathmandu and Pokhara, Nepal

The prevalence of infestation with head lice and body lice, Pediculus spp. (Phthiraptera: Pediculidae) and pubic (crab) lice Pthirus pubis (L.) (Phthiraptera: Pthiridae), was recorded from 484 people in Nepal. The prevalence of head lice varied from 16% in a sample of people aged 10-39 years of age, to 59% in street children. Simultaneous infestations with head and body lice (double infestations) varied from 18% in slum children to 59% in street children.     

Pyrethroid resistance mechanisms in the head louse Pediculus capitis from Israel: implications for control

In Israel, the head louse, Pediculus capitis, developed resistance to DDT through the extensive use of this insecticide until the 1980s. In 1991, permethrin was introduced for control of DDT resistant P. capitis in Israel, leading to control failure of this pyrethroid insecticide by 1994. Pyrethroid resistance of P. capitis in Israel extends to phenothrin, which has not been used for louse control. We identified a glutathione S-transferase(GST)-based mechanism of DDT resistance in the Israeli head lice. This GST mechanism occurred before 1989, while permethrin resistance in P. capitis developed after 1994, suggesting that the main GST resistance mechanism selected by DDT use does not confer any pyrethroid cross-resistance. Esterase activity levels were equivalent in pyrethroid resistant and susceptible P. capitis field-collected in Israel, and in a susceptible strain of P. humanus, the body louse, indicating no involvement of any esterase-based mechanism in resistance. A weak monooxygenase-based permethrin metabolism resistance mechanism was the only factor identified which could account for any of the observed pyrethroid resistance in P. capitis. However, the lack of synergism of phenothrin resistance by piperonyl butoxide suggests that a non-oxidative mechanism is also present in the resistant lice. Therefore it seems probable that pyrethroid resistance in Israeli P. capitis is due to a combination of nerve insensitivity (knockdown resistance or 'kdr') and monooxygenase resistance mechanisms.     

Permethrin resistance in the head louse Pediculus capitis from Israel

Head lice, Pediculus capitis , were collected from children aged 3–12 years in Maale Adumin, a town near Jerusalem, after reports of control failure with the pyrethroid insecticide permethrin. A total of 1516 children were examined: living lice and eggs were found on 12.1% of the children; or another 22.8% of the children only nits were found. Twice as many girls as boys (8.1% v 4%) were infested with lice and or nits. Head lice collected from infested children were exposed to permethrin impregnated filter-papers. Log time probit mortality (ltp) regression lines were calculated for mortality data and compared to ltp lines for a similar collection of head lice made in 1989. The regression lines for the two years were significantly different, with a 4-fold decrease in susceptibility at the LT50 level between 1989 and 1994. The slopes of the lines also suggested that the 1994 population was more heterogenous in its response to permethrin than the 1989 population. In contrast, a laboratory population of body lice (Pediculus humanus) tested with the same batch of permethrin-impregnated papers showed a slight but non-significant increase in susceptibility between 1989 and 1994. The results suggest that resistance to pyrethroids has developed rapidly among head lice since permethrin was introduced in 1991 as a pediculicide in Israel.     

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.     

Prevalence of nits and lice in samples of cut hair from floors of barbershops and beauty parlors in Belo Horizonte, Minas Gerais State, Brazil

A louse survey based on samples of cut hair collected from floors of barbershops and beauty parlors was conducted in Belo Horizonte, Minas Gerais State, Brazil, from October 1984 to April 1985, as an alternative way to determine the prevalence of pediculosis capitis in the population. Of 475 samples examined for nits, nymphs, or adults of Pediculus capitis, 140 were infested (29.5%). A total of 58 lice and 3,553 nits were found in 33,632.9 g of hair collected, giving a ratio of 0.10 nit/g. Almost 29% of the nits were viable and capable of being transmitted after hatching. There was significant difference among the infestation rates by socioeconomic levels, and samples from barbershops with male customers were the most infested. Based upon the number of haircuts in each sample, we estimated that 5 or 6% of the population might be infested by this species.     

Rural life, lower socioeconomic status and parasitic infections

This study was conducted both to assess the prevalence of parasitic infections in two neighboring villages of Manisa province in Turkey, with different socioeconomic levels and investigate the influences of some individual and environmental factors on these infections. A total of 100 school children were enrolled and their cellophane tape and stool samples were examined for parasites. Pediculus capitis infestation was diagnosed by visual inspection of the hair. Although the prevalences of both intestinal parasitosis and pediculosis were high in both villages, there was a statistically significant difference for pediculosis, but not for intestinal parasitosis. Lack of social security and father's regular job were found to be highly correlated with all parasitic infections. Pediculosis was more common in younger children, girls and those in crowded families. These results indicate not only the high prevalence of parasitic infections, but also the urgent need for the improvement of basic health services and infrastructure in the rural areas, crowded with poorer immigrant population.     

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.     

Large-scale monitoring of imidacloprid susceptibility in the cat flea, Ctenocephalides felis

Although on-animal topical treatment with compounds such as imidacloprid has revolutionized the control of the cat flea, Ctenocephalides felis (Bouché) (Siphonaptera: Pulicidae), the development of insecticide resistance is a continuing threat. As part of a highly co-ordinated and unprecedented resistance monitoring programme for C. felis, 1437 flea isolates were collected by veterinary clinics in Australia, Germany, France, the U.K. and 29 states in the U.S.A. from 2002 to 2009. About 65% of the collections were made from June to October each year and 71% of the collections were from cats. Collections of flea eggs were sent to one of five different laboratories, where they were tested with a diagnostic dose of imidacloprid (3 p.p.m.) applied to larval flea-rearing medium. Of the 1437 collections received, 1064 contained adequate numbers of eggs for testing. Of these isolates, untreated eggs failed to hatch in 22.7% and were not considered valid bioassays. Survival rates >5% and development of adult fleas (a threshold for further testing) occurred in only 22 isolates. They were re-tested with the same diagnostic dose and none produced >5% adult emergence. Complete dose-response bioassays were performed on three of the isolates that had triggered a second test and produced slopes, intercepts and LC(50) values similar to those for existing susceptible laboratory strains. Results confirmed sustained susceptibility of C. felis to imidacloprid, despite its widespread use for over a decade.     

Antagonism between Beauveria bassiana and imidacloprid when combined for Bemisia argentifolii (Homoptera: Aleyrodidae) control

Imidacloprid and the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin are both used to control the whitefly Bemisia argentifolii Bellows & Perring. We tested whether the two control strategies acted additively, synergistically, or antagonistically when combined for whitefly control. We found antagonism in that B. bassiana inhibited the effectiveness of imidacloprid. When B. bassiana was combined with imidacloprid, insect response was either less than or similar to (depending on B. bassiana rates) that when imidacloprid was used alone. Adding imidacloprid to B. bassiana treatments always increased mortality, but the increase was less than additive. Beauveria bassiana spore germination and colony formation were not inhibited by imidacloprid in vitro, and B. bassiana did not adsorb or degrade imidacloprid in a tank mix. We hypothesize that B. bassiana caused a behavioral response that reduced insect feeding and uptake of imidacloprid.     

Dynamics of imidacloprid resistance and cross-resistance in the brown planthopper, Nilaparvata lugens

Extensive use of imidacloprid for suppressing the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), has placed heavy selection pressure on the target insect. A systematic study was carried out to determine imidacloprid resistance dynamics and cross-resistance. Data collected from a 3-year study (2005–2007) showed that in 2005, the resistance levels in Nanning (Guangxi), Haiyan (Zhejiang), and Nanjing and Tongzhou (Jiangsu) populations ranged from 200- to 799-fold compared with the susceptible strain. However, the resistance levels decreased to 135- to 233-fold in 2007, after reduced application of the chemical. A laboratory population was challenged with imidacloprid in successive generations. After 23 generations, the resistance ratio had increased from 200- to 1 298-fold. Continuous selection with imidacloprid could increase the resistance level even more than has already been developed in the population. Stopping selection with imidacloprid led to a rapid decrease of resistance from 759- to 114-fold after 17 generations. Resistance levels then became stable without decreasing any further. A similar result was also obtained from a study involving a field population (resistance ratio = 625-fold) collected from Tongzhou. At first, the population showed a rapid decrease in resistance right after imidacloprid selection was stopped, and then the resistance stabilized at a level of 105–129-fold. More interestingly, resistance increased again when selection was resumed. In addition, the resistant strain selected with imidacloprid showed substantial cross-resistance to imidaclothiz, thiacloprid, and acetamiprid, and slight levels of cross-resistance to dinotefuran and thiamethoxam, but no obvious cross-resistance to nitenpyram, buprofezin, and fipronil. The information from this study is valuable for formulating resistance-management strategies against N. lugens .     

Electromyography of superficial and deep neck muscles during isometric, voluntary, and reflex contractions

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.     

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.     

Intestinal parasites and ectoparasites in the V region, Chile: study in the Psychiatric Hospital of Putaendo

A prospective study was carried out in 229 chronic patients (of both sexes) from the Psychiatric Hospital of Putaendo, in order to find out the frequency of intestinal parasites and/or commensals in the period 1987-1989. One hundred and ninety four (84.7%) out of the 229 studied patients were infected by parasites and/or commensals. The high prevalence of commensals Entamoeba coli (55.0%) and Endolimax nana (50.5%) became more evident. Among the parasites, the most frequent was Trichuris trichiura (41.5%). The presence of Pediculus humanus capitis and lesions suggestive of those produced by Sarcoptes scabiei were detected in 7.2 and 0.6 of the examined patients. The results obtained show the high frequency of intestinal infections by parasites and commensals in the patients of the studied hospital.     

Evidence from double infestations for the specific status of human head lice and body lice (Anoplura)

Abstract Samples of head lice and body lice obtained from Ethiopians suffering from double infestations were mounted onto microscope slides and measured. The mean length of body lice (♀ 4.4mm; ♂ 3.8mm) was greater than that of head lice (♀ 3.5 mm; ♂ 2.9mm), but the best discriminant was the length of the tibia of the middle leg (♀ 425/296 μ♂421/291 μ). No intermediate specimens were found in these double infestations, although intermediates can can be produced experimentally by cross-mating. Since populations of head lice and body lice remain distinct it is concluded that they represent two distinct species, Pediculus capitis De Geer and P. humanus Linneaus.     

Lipid and protein composition at different developmental stages of Pediculus capitis (Arthropoda, Phthiraptera).

Protein and lipid compositions were studied at different developmental stages of Pediculus capitis De Geer 1778. Phosphatidylcholine was found to be the predominant lipid at all stages and in both sexes. Palmitic and oleic acids were the main fatty acids throughout the 3 stages studied. A marked decline was observed in the total lipid content and triacylglyceride concentration during development, suggesting that their consumption is an energy source. The electrophoretic mobility revealed the predominance of a 320-kDa protein in eggs and adult females, whereas 2 major proteins of 514 and 439 kDa were found in nymphs, as well as in male and female adults. Two very high density lipoprotein fractions were isolated by ultracentrifugation of egg cytosol in a density gradient of NaBr. Both reserve lipoproteins contained phospholipids and triacylglycerols as the predominant lipids and a protein band of around 320 kDa. The structure of this band is likely to be similar to that found in females in a vitellogenic state.     

虱目裂化线粒体基因组研究进展

虱目是哺乳类和鸟类体表的专性寄生虫。在虱科、阴虱科、长角鸟虱科和兽羽虱科的某些寄生虱种中发现了线粒体基因组裂化现象, 其线粒体基因组裂化成了多个环状的线粒体染色体, 如体虱(Pediculus humanus)、头虱(pediculus capitis)和阴虱(Pthirus pubis)的线粒体基因组分别裂化形成20个、20个和14个微环染色体。微环染色体可能是基因删除和同源重组的结果, 关于线粒体基因组裂化的具体原因和机制, 目前并不清楚, 推测可能是进化选择或随机遗传漂变的结果或与线粒体单链DNA结合蛋白的缺失有关。鉴于线粒体基因组裂化研究对于深入理解线粒体的起源和进化方面具有重要意义, 文章以虱目裂化线粒体基因组为主线, 列举了动物裂化线粒体基因组和裂化特征, 阐述了虱目裂化线粒体基因组的研究现状, 分析了虱目线粒体基因组裂化的类型、原因和机制, 并对该领域未来的研究方向进行了展望。     

The fumigant and repellent activity of aliphatic lactones against Pediculus humanus capitis (Anoplura: Pediculidae)

New alternative insecticides are necessary for the chemical control of head lice. In this study the fumigant knockdown time 50% (KT50) and repellency index (RI) of three aliphatic lactones was compared with two essential oils and DDVP, against permethrin-resistance Pediculus humanus capitis from Argentina. In the fumigant assay, none of the lactones were effective compared to the highest activity of eucalyptus (KT50 15.53 m). In the repellency test, the three lactones were equally or more effective (RI ranging from 60.50 to 76.68) than the positive control (piperonal). These lactones are promising as head lice repellents.     

Do nit removal formulations and other treatments loosen head louse eggs and nits from hair?

Eggs of the head louse, Pediculus capitis De Geer (Phthiraptera: Pediculidae), are difficult to remove because the female louse fixes them to hairs using a proteinaceous secretion that hardens within seconds. The persistent eggshells are harmless but unsightly and are often mistaken for an active infestation. Combing with a fine comb (nit comb) does not readily remove the eggs or empty eggshells because of the resilience of the fixative and both folk remedies and medical products have claimed to facilitate their removal. Measurement of the force required to initiate sliding of the egg fixative using a slip-peel tester was unable to detect evidence that any of three products which claimed to have egg-loosening properties (Step 2™ Nit Removal System, Clear^® Lice Egg Remover, RID^® Lice Egg Loosener Gel) had any activity or exerted any effect on the egg fixative beyond the lubricating effects conveyed by water or conventional hair conditioner.