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.     

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.     

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.     

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.     

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.     

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.     

Immunization of Atlantic salmon against the salmon louse: identification of antigens and effects on louse fecundity

Injection of extracts derived from adult caligid copepods induced a partial immunity to Lepeophtheirus salmonis in Atlantic salmon. Antigens were derived from the supernatant of adult lice extracts and were partially purified by Con A affinity chromatography. The antigens were also present in the pellet derived from adult lice extracts, Immunohistochemistry showed that antibodies present in the serum of rats immunized with the Con A purified extract bound predominantly to the gut of L. salmonis. Components of apparent sizes > 205 000, 165 000, 133 000, 130 000, 125 000, 114 000, 110 000, 96 000, 82 000, 78 000, 65 000, 46 000, 35 000, 31 000 and < 29 000 were present in the extract. Although the numbers of attached lice were initially higher on those fish in the immunized group, throughout the course of the challenge experiment the total numbers of lice did not vary greatly between the immunized or control groups of fish. Initially, an overall average of about 17 attached stages were recorded from each fish sampled and by the end of the experiment this figure had fallen to about five adult lice per fish. However, compared with control fish fewer gravid female lice were present on immunized fish and furthermore these lice possessed fewer eggs (P<0.01). No major differences in egg hatching success were recorded. Further exploitation of this would require the isolation and purification of the antigens responsible for the observed effects. The possibilities for the development of a salmon louse vaccine are promising.     

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.     

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.     

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.     

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.     

Molecular evolution of Pediculus humanus and the origin of clothing

The human head louse (Pediculus humanus capitis) and body louse (P. humanus corporis or P. h. humanus) are strict, obligate human ectoparasites that differ mainly in their habitat on the host : the head louse lives and feeds exclusively on the scalp, whereas the body louse feeds on the body but lives in clothing. This ecological differentiation probably arose when humans adopted frequent use of clothing, an important event in human evolution for which there is no direct archaeological evidence. We therefore used a molecular clock approach to date the origin of body lice, assuming that this should correspond with the frequent use of clothing. Sequences were obtained from two mtDNA and two nuclear DNA segments from a global sample of 40 head and body lice, and from a chimpanzee louse to use as an outgroup. The results indicate greater diversity in African than non-African lice, suggesting an African origin of human lice. A molecular clock analysis indicates that body lice originated not more than about 72,000 +/- 42,000 years ago; the mtDNA sequences also indicate a demographic expansion of body lice that correlates with the spread of modern humans out of Africa. These results suggest that clothing was a surprisingly recent innovation in human evolution.     

Determination of Knockdown Resistance (kdr) Allele Frequencies (T929I mutation) in Head Louse Populations from Mexico,Canada, and Peru

The head louse Pediculus humanus capitis (De Geer) is a hematophagous ectoparasite that inhabits the human scalp. The infestations are asymptomatic; however, skin irritation from scratching occasionally may cause secondary bacterial infections. The present study determined the presence and frequency of the knockdown resistance (kdr) mutation T929I in 245 head lice collected from Mexico, Peru, and Canada. Head lice were collected manually using a comb in the private head lice control clinic. Allele mutation at T9291 was present in 100% of the total sampled populations (245 lice) examined. In addition, 4.89% of the lice were homozygous susceptible, whereas 6.93% heterozygous and 88.16% homozygous were resistant, respectively. This represents the second report in Mexico and Quebec and fist in Lima.     

How long do louse eggs take to hatch? A possible answer to an age‐old riddle

There are no rigorous data on how long eggs of the head louse, Pediculus capitis (Phthiraptera: Pediculidae), take to hatch. Pediculicide users often report re‐infestations after apparently successful treatments in the absence of infective contacts. This study aimed to resolve the question of whether some louse eggs hatch after the completion of treatment, thereby giving rise to a new infestation. Data were extracted from the records of lice collected after treatments in 20 clinical intervention trials. All datasets were eliminated except those in which only newly hatched louse nymphs were found prior to the final assessment. This excluded the possibility that new eggs were laid after the first treatment and thus any young lice found must have originated from eggs laid before the start of treatment. This identified 23 of 1895 (1.2%) records with evidence of louse nymphs emerging at 13 days or more after the first treatment, 3–6 days longer than previous estimates. Current treatment regimens for pediculicides of two applications 7–10 days apart appear inadequate, which may explain continuing infestation in the community. Therefore, it is suggested that a revised approach using three treatments applied at intervals of 1 week should prevent the survival of any nymphs and their development into a new generation of adults.     

Resistance to benzoylphenyl urea insecticides in Australian populations of the sheep body louse

Abstract.  A laboratory bioassay based on the failure of eggs laid by diflubenzuron-treated sheep body lice Bovicola ovis (Schrank) (Phthiraptera; Trichodectidae) to produce nymphs is described. The test is capable of detecting benzoylphenyl urea-resistant populations. A susceptible discriminating dose (topical treatment of female lice with 0.10 μg diflubenzuron) suitable for screening suspect resistant populations is suggested but testing of further populations that are naïve to these insect growth regulator insecticides is warranted.     

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.     

The molecular targets of ivermectin and lotilaner in the human louse Pediculus humanus humanus: New prospects for the treatment of pediculosis

Control of infestation by cosmopolitan lice (Pediculus humanus) is increasingly difficult due to the transmission of parasites resistant to pediculicides. However, since the targets for pediculicides have no been identified in human lice so far, their mechanisms of action remain largely unknown. The macrocyclic lactone ivermectin is active against a broad range of insects including human lice. Isoxazolines are a new chemical class exhibiting a strong insecticidal potential. They preferentially act on the γ-aminobutyric acid (GABA) receptor made of the resistant to dieldrin (RDL) subunit and, to a lesser extent on glutamate-gated chloride channels (GluCls) in some species. Here, we addressed the pediculicidal potential of isoxazolines and deciphered the molecular targets of ivermectin and the ectoparasiticide lotilaner in the human body louse species Pediculus humanus humanus. Using toxicity bioassays, we showed that fipronil, ivermectin and lotilaner are efficient pediculicides on adult lice. The RDL (Phh-RDL) and GluCl (Phh-GluCl) subunits were cloned and characterized by two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Phh-RDL and Phh-GluCl formed functional homomeric receptors respectively gated by GABA and L-glutamate with EC₅₀ values of 16.0 μM and 9.3 μM. Importantly, ivermectin displayed a super agonist action on Phh-GluCl, whereas Phh-RDL receptors were weakly affected. Reversally, lotilaner strongly inhibited the GABA-evoked currents in Phh-RDL with an IC₅₀ value of 40.7 nM, whereas it had no effect on Phh-GluCl. We report here for the first time the insecticidal activity of isoxazolines on human ectoparasites and reveal the mode of action of ivermectin and lotilaner on GluCl and RDL channels from human lice. These results emphasize an expected extension of the use of the isoxazoline drug class as new pediculicidal agents to tackle resistant-louse infestations in humans.     

Embryonic development of human lice: rearing conditions and susceptibility to spinosad

The embryonic development of human lice was evaluated according to the changes in the morphology of the embryo observed through the transparent chorion. Based on ocular and appendage development, three stages of embryogenesis were established: early, medium, and late. Influence of temperature and relative humidity (RH) on the laboratory rearing of Pediculus humanus capitis eggs was assessed. The optimal ranges for temperature and RH were 27-31 degrees C and 45-75%. The susceptibility of head [corrected] louse eggs to insecticide spinosad (a macrocyclic lactone) was assessed by immersion method. The results showed similar susceptibility to spinosad in early, medium, and late stages of head lice eggs. In addition, this study showed similar susceptibility of head and body lice eggs to spinosad, an insecticide that has not been used as pediculicide in Argentina (lethal concentration 50: 0.01%).