Louse Pediculus Humanus Research Articles

First Case Report of Louse – Borne Relapsing Fever in Saudi Arabia

Relapsing fever is endemic in some parts of the world such as Africa, South America, and Far East.1-3 Epidemics have occurred among refugees and war victims in some parts of Africa.4,5 There is very little information about this infection in Saudi Arabia. The prevalence or incidence in Saudi Arabia is unknown. Its apparent rarity may be due to under diagnosis and under reporting. A high index of suspicion in appropriate clinical situations will lead to its early recognition and treatment. Relapsing fever is an acute febrile illness caused by blood spirochetes belonging to genus borrelia. This spirochete can be acquired through the bite of an infected soft tick (Ornithodoros species) or contact with the hemolymph of an infected human body louse (Pediculus humanus) and thus constituting two types of relapsing fever (RF) depending upon the responsible vector i.e. Tick – borne relapsing fever (TBRF) and Louse – borne relapsing fever (LBRF). It is characterized by recurrent cycles of pyrexia which are separated by intervals of apparent recovery. During pyrexia, organisms can be found in blood and that is the only way of reliable diagnosis in many situations.6,7 While during afebrile period, organisms hide themselves in spleen, liver and even central nervous system.

Prevalence of Pediculus humanus capitis in a school of low socio-economy area in Rampur (U.P), India

The prevalence of head louse Pediculus humanus capitis on the school children of a low socio-economy area of Rampur, India was found to be 56% (n=300). Female children appeared lousier. However, the hygienic condition and their density appeared to have negligible effect on head louse.

Eucalyptus essential oil toxicity against permethrin-resistant Pediculus humanus capitis (Phthiraptera: Pediculidae)

During the past decades, chemical control against the head louse Pediculus humanus capitis De Geer has been based in the application of products containing permethrin. The repetitive overuse of pediculicides has resulted in the development of high levels of resistance to one or more of these products worldwide. Essential oils obtained from aromatic plants like Eucalyptus are good and safe alternatives due to their low toxicity to mammals and easy biodegradability. In the present study, we reported the chemical composition of Eucalyptus dunnii and Eucalyptus gunni, and the fumigant activity of five Eucalyptus essential oils and their main compounds against permethrin-resistant head lice from Argentina. The most effective essential oils were Eucalyptus sideroxylon, Eucalyptus globulus ssp globulus, and Eucalyptus globulus ssp maidenii, with knockdown time 50% (KT(50)) values of 24.75, 27.73, and 31.39 min. A linear regression analysis between percentage of 1,8-Cineole and KT(50) values of the essential oils showed a significant correlation at a p < 0.01. Since Eucalyptus essential oils showed to be effective against head lice and are classified as safer compounds, they can be employed into pediculicide formulations.

Direct evidence of the cyclooxygenase pathway of prostaglandin synthesis in arthropods: Genetic and biochemical characterization of two crustacean cyclooxygenases

Prostaglandins, well-known lipid mediators in vertebrate animals, have also shown to play certain regulatory roles in insects and other arthropods acting on reproduction, immune system and ion transport. However, knowledge of their biosynthetic pathways in arthropods is lacking. In the present study, we report the cloning and expression of cyclooxygenase (COX) from amphipod crustaceans Gammarus spp and Caprella spp. The amphipod COX proteins contain key residues shown to be important for cyclooxygenase and peroxidase activities. Differently from all other known cyclooxygenases the N-terminal signal sequence of amphipod enzymes is not cleaved during protein expression in mammalian cells. The C-terminus of amphipod COX is shorter than that of mammalian isoforms and lacks the KDEL(STEL)-type endoplasmic reticulum retention/retrieval signal. Despite that, amphipod COX proteins are N-glycosylated and locate similarly to the vertebrate COX on the endoplasmic reticulum and nuclear envelope. Both amphipod COX mRNAs encode functional cyclooxygenases that catalyze the transformation of arachidonic acid into prostaglandins. Using bioinformatic analysis we identified a COX-like gene from the human body louse Pediculus humanus corporis genome that encodes a protein with about 30% sequence identity with human COX-1 and COX-2. Although the COX gene is known to be absent from genomes of Drosophila sp., Aedes aegypti, Bombyx mori, and other insects, our studies establish the existence of the COX gene in certain lineages within the insect world.

Impact of ivermectin drug combinations on Pediculus humanus capitis infestation in primary schoolchildren of south Indian rural villages

Antifilarial drug combinations including ivermectin provide antifilarial activity with ancillary benefits on intestinal helminths and ectoparasites, such as chiggers and lice. The impact of single oral dose of antifilarial drugs, viz; (1) diethylcarbamazine (DEC) alone, (ii) DEC + albendazole (ALB), (iii) ivermectin (IVR) + DEC and (iv) IVR + ALB, was determined, on the head louse (Pediculus humanus capitis) in primary school children in a rural community in south India. Primary school children (n = 534) of age 6-10 years from four villages of South India were examined for the presence of head lice before and after single dose of DEC + ivermectin drug combination. The effectiveness and the duration of cure sustained by these drugs were quantified. The head louse was examined by "combing method" during post-treatment periods at 15, 45, 60 and 75 days interval. The antifilarial drug consumption rate was similar (96-98%) in all treatment arms. In pre-treatment survey the prevalence of head lice in children administered with DEC, DEC + ALB, IVR + DEC and IVR + ALB arm was 86%, 80%, 87% and 80%, respectively, with the latter two arms demonstrating significant reduction in louse infestation (P < 0.05) for 60 days. Single dose with IVR combination demonstrates a greater impact in reducing head louse infestation in the endemic rural communities for nearly 60 days. Therefore, in regions such as Africa where ivermectin is part of the antifilariasis campaign, this drug will have an additional benefit in reducing head lice infestation.

Reconstructing the phylogeny of 21 completely sequenced arthropod species based on their motor proteins.

BackgroundMotor proteins have extensively been studied in the past and consist of large superfamilies. They are involved in diverse processes like cell division, cellular transport, neuronal transport processes, or muscle contraction, to name a few. Vertebrates contain up to 60 myosins and about the same number of kinesins that are spread over more than a dozen distinct classes.ResultsHere, we present the comparative genomic analysis of the motor protein repertoire of 21 completely sequenced arthropod species using the owl limpet Lottia gigantea as outgroup. Arthropods contain up to 17 myosins grouped into 13 classes. The myosins are in almost all cases clear paralogs, and thus the evolution of the arthropod myosin inventory is mainly determined by gene losses. Arthropod species contain up to 29 kinesins spread over 13 classes. In contrast to the myosins, the evolution of the arthropod kinesin inventory is not only determined by gene losses but also by many subtaxon-specific and species-specific gene duplications. All arthropods contain each of the subunits of the cytoplasmic dynein/dynactin complex. Except for the dynein light chains and the p150 dynactin subunit they contain single gene copies of the other subunits. Especially the roadblock light chain repertoire is very species-specific.ConclusionAll 21 completely sequenced arthropods, including the twelve sequenced Drosophila species, contain a species-specific set of motor proteins. The phylogenetic analysis of all genes as well as the protein repertoire placed Daphnia pulex closest to the root of the Arthropoda. The louse Pediculus humanus corporis is the closest relative to Daphnia followed by the group of the honeybee Apis mellifera and the jewel wasp Nasonia vitripennis. After this group the rust-red flour beetle Tribolium castaneum and the silkworm Bombyx mori diverged very closely from the lineage leading to the Drosophila species.

Prevalence ofkdr-like Mutations Associated with Pyrethroid Resistance in Human Head Louse Populations in Japan

Pyrethroid insecticides play very important roles in the control of pediculosis, which is caused by human head louse (Pediculus humanus capitis De Geer) worldwide. The development of head louse resistance to pyrethroid pediculicides has become a global issue during the last two decades. Pyrethroid resistance is associated with amino acid substitutions in the alpha-subunit of the para-sodium channel gene; these substitutions are termed kdr-like mutations. The frequencies of four mutations (D11E, M815I, T929I, and L932F) in the sodium channel gene were studied in human head louse colonies collected from Japan by using SNaPshot method. A total of 630 head lice collected from 282 infested people were analyzed, and it was found that 55 lice of 19 colonies homozygously or heterozygously possessed kdr-like genes, in which the four mutations existed concomitantly. This suggested that the quadruple mutant haplotype is a common feature of the kdr genes of pandemic head lice. The frequencies of the occurrence of resistant genes in the total individuals tested and resistant gene-carrying colonies were 8.7 (55/630) and 6.7% (19/263), respectively. Because the resistant gene was detected in the colonies collected from 11 of the 22 prefectures surveyed, it is speculated that resistant head lice are already spread extensively in Japan. This was the first large-scale survey of pyrethroid resistant head lice in Japan.

In Vitro Screening of Anti-lice Activity of Pongamia pinnata Leaves

Growing patterns of pediculocidal drug resistance towards head louse laid the foundation for research in exploring novel anti-lice agents from medicinal plants. In the present study, various extracts of Pongamia pinnata leaves were tested against the head louse Pediculus humanus capitis. A filter paper diffusion method was conducted for determining the potential pediculocidal and ovicidal activity of chloroform, petroleum ether, methanol, and water extracts of P. pinnata leaves. The findings revealed that petroleum ether extracts possess excellent anti-lice activity with values ranging between 50.3% and 100% where as chloroform and methanol extracts showed moderate pediculocidal effects. The chloroform and methanol extracts were also successful in inhibiting nymph emergence and the petroleum ether extract was the most effective with a complete inhibition of emergence. Water extract was devoid of both pediculocidal and ovicidal activities. All the results were well comparable with benzoyl benzoate (25% w/v). These results showed the prospect of using P. pinnata leave extracts against P. humanus capitis in difficult situations of emergence of resistance to synthetic anti-lice agents.

VectorBase: a data resource for invertebrate vector genomics

VectorBase (http://www.vectorbase.org) is an NIAID-funded Bioinformatic Resource Center focused on invertebrate vectors of human pathogens. VectorBase annotates and curates vector genomes providing a web accessible integrated resource for the research community. Currently, VectorBase contains genome information for three mosquito species: Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus, a body louse Pediculus humanus and a tick species Ixodes scapularis. Since our last report VectorBase has initiated a community annotation system, a microarray and gene expression repository and controlled vocabularies for anatomy and insecticide resistance. We have continued to develop both the software infrastructure and tools for interrogating the stored data.

Hyaluronidase of Bloodsucking Insects and Its Enhancing Effect on Leishmania Infection in Mice

BackgroundSalivary hyaluronidases have been described in a few bloodsucking arthropods. However, very little is known about the presence of this enzyme in various bloodsucking insects and no data are available on its effect on transmitted microorganisms. Here, we studied hyaluronidase activity in thirteen bloodsucking insects belonging to four different orders. In addition, we assessed the effect of hyaluronidase coinoculation on the outcome of Leishmania major infection in BALB/c mice.Principal FindingsHigh hyaluronidase activity was detected in several Diptera tested, namely deer fly Chrysops viduatus, blackflies Odagmia ornata and Eusimilium latipes, mosquito Culex quinquefasciatus, biting midge Culicoides kibunensis and sand fly Phlebotomus papatasi. Lower activity was detected in cat flea Ctenocephalides felis. No activity was found in kissing bug Rhodnius prolixus, mosquitoes Anopheles stephensi and Aedes aegypti, tse-tse fly Glossina fuscipes, stable fly Stomoxys calcitrans and human louse Pediculus humanus. Hyaluronidases of different insects vary substantially in their molecular weight, the structure of the molecule and the sensitivity to reducing conditions or sodium dodecyl sulphate. Hyaluronidase exacerbates skin lesions caused by Leishmania major; more severe lesions developed in mice where L. major promastigotes were coinjected with hyaluronidase.ConclusionsHigh hyaluronidase activities seem to be essential for insects with pool-feeding mode, where they facilitate the enlargement of the feeding lesion and serve as a spreading factor for other pharmacologically active compounds present in saliva. As this enzyme is present in all Phlebotomus and Lutzomyia species studied to date, it seems to be one of the factors responsible for enhancing activity present in sand fly saliva. We propose that salivary hyaluronidase may facilitate the spread of other vector-borne microorganisms, especially those transmitted by insects with high hyaluronidase activity, namely blackflies (Simuliidae), biting midges (Ceratopogonidae) and horse flies (Tabanidae).

A highly efficacious pediculicide based on dimeticone: Randomized observer blinded comparative trial

BackgroundInfestation with the human head louse (Pediculus humanus capitis) occurs worldwide. Existing treatment options are limited, and reports of resistance to commonly used pediculicides have been increasing. In this trial we assessed the efficacy of a product containing a high (92%) concentration of the silicone oil dimeticone (identical in composition to NYDA®), as compared to a 1% permethrin lotion.MethodsRandomized, controlled, observer blinded clinical trial. Participants were recruited from a poor urban neighbourhood in Brazil where pediculosis capitis was highly prevalent. To minimize reinfestation during the trial, participants (145 children aged 5–15 years with head lice infestations) were transferred to a holiday resort outside the endemic area for a period of 9 days. Two applications of dimeticone or 1% permethrin were done, seven days apart. Outcome measures were defined as cure (absence of vital head lice) after first application and before and after second applications, degree of itching, cosmetic acceptability, and clinical pathology.ResultsOverall cure rates were: day 2 – dimeticone 94.5% (95% CI: 86.6% – 98.5%) and permethrin 66.7% (95% CI: 54.6% – 77.3%; p < 0.0001); day 7 – dimeticone 64.4% (95% CI: 53.3% – 75.3%) and permethrin 59.7% (95% CI: 47.5% – 71.1%; p = 0.5); day 9 – dimeticone 97.2% (95% CI: 90.3% – 99.7%) and permethrin 67.6% (95% CI: 55.4%-78.2%); p < 0.0001). Itching was reduced similarly in both groups. Cosmetic acceptability was significantly better in the dimeticone group as compared to the permethrin group (p = 0.01). Two mild product-related incidents occurred in the dimeticone group.ConclusionThe dimeticone product is a safe and highly efficacious pediculicide. Due to its physical mode of action (interruption of the lice's oxygen supply of the central nervous system), development of resistance is unlikely.Trial registrationCurrent Controlled Trials ISRCTN15117709.

Determination of Permethrin Resistance Allele Frequency of Human Head Louse Populations by Quantitative Sequencing

A quantitative sequencing (QS) protocol that detects the frequencies of sodium channel mutations (M815I, T917I, and L920F) responsible for knockdown resistance in permethrin-resistant head lice (Pediculus humanus capitis De Geer) was tested as a population genotyping method for use as a preliminary resistance monitoring tool. Genomic DNA fragments of the sodium channel a-subunit gene that encompass the three mutation sites were polymerase chain reaction (PCR)-1 amplified from individual head lice with either resistant or susceptible genotypes, and combined in various ratios to generate standard DNA template mixtures for QS. After sequencing, the signal ratios between resistant and susceptible nucleotides were calculated and plotted against the corresponding resistance allele frequencies. Quadratic regression coefficients of the plots were close to 1, demonstrating that the signal ratios are highly correlated with the resistance allele frequencies. Resistance allele frequencies predicted by QS, using either "pooled DNA" (DNA extracted from individual louse specimens and pooled) or "pooled specimen DNA" (DNA simultaneously extracted from multiple louse specimens), agreed well with those determined by individual sequencing, confirming the reliability and accuracy of QS as a population genotyping method and validating our approach of using the pooled specimen DNA as the DNA template for QS. Our protocol for QS was determined to be highly reliable for the prediction of resistance allele frequencies higher than approximately 7.4% at the 95% confidence level. According to the resistance allele frequencies determined by QS, pyrethroid resistance varies substantially among different geographical regions, emphasizing the importance of early resistance detection and proper management strategies.

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

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((R)), 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 >or= 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.

Development of Tribolium castaneum

With the publication of the Tribolium castaneum genome (Richards et al. 2008), carefully annotated insects genomes are now available for three insect orders: the flies (Diptera: 12 Drosophila species and two mosquito species: Anopheles gambiae, Aedes aegypti), the bees, wasps, and ants (Hymenoptera: Apis mellifera), and the beetles (Coleoptera) to which Tribolium belongs. Furthermore, sequencing has been (partially) finished and annotation is in progress for several other insect genomes: the mosquito (Diptera) Culex pipiens, the parasitic wasp (Hymenoptera) Nasonia vitripennis, and two related Nasonia species, the silk worm (Lepidoptera) Bombyx mori and three hemimetabolous insects species: the blood-sucking bug (Hemiptera) Rhodnius prolixus, the pea aphid (Hemiptera) Acyrthosiphon pisum, and the human louse (Phthiraptera) Pediculus humanus (for review on recent advances in insects genomics see Grimmelikhuijzen et al. 2007). Together, these data provide an impressive basis for comparative insect genomics. They will allow us to reconstruct the common features of the genomes of holometabolous insects and they will reveal features of the basal genomes present in the ancestor of hemiand holometabolous insects. They also will help to resolve phylogenetic questions. One fascinating outcome from recent phylogenomic studies is a new tree of holometabolous insects, which locates the bees and wasps (Hymenoptera) at the base of the radiation of holometabolous insects (Savard et al. 2006; Zdobnov and Bork 2007; see also Misof et al. 2000 for a more conventional approach). Classical phylogeny had given the beetles a basal position within the tree (Grimaldi and Engels 2005). The new phylogeny has important implications for the evolutionary analysis of developmental processes. Beetles are the only holometabolous insect order with definite short-germ-band development (Sander 1976; Schwalm 1988; Davis and Patel 2002). Short-germ-band embryos harbor anlagen only of anterior segments (usually head and thorax) prior to gastrulation while the posterior (abdominal) segments form from a growth zone. This mode of the development is common to all hemimetabolous insects while all holometabolous insects, with the exception of the beetles, show long-germ-band development. In longgerm-band embryos, all segment anlagen are present prior to gastrulation and all segments form either simultaneously or sequentially within a narrow time window. In addition to the mode of segmentation, the organization of extraembryonic membranes of beetles (size and position of serosal anlagen, early amnion formation) is more similar to that of hemimetabolous insects (Schwalm 1988; van der Zee et al. 2005; Panfilio 2008). Since the holometabolous insects clearly are monophyletic, the new phylogeny offers two alternative interpretations. First, it is possible that the common ancestor of all holometabolous insects had already acquired long-germ development. According to this assumption, short-germ development in beetles would be a secondary character. This might explain why long-germ development can be observed among beetles (Patel et al. 1994). It also would fit the observation that the early fate map of the DV axis in Tribolium is very similar to that of long-germ embryos (Chen et al. 2000). A second interpretation of the new phylogeny is that short germ development Dev Genes Evol (2008) 218:115–118 DOI 10.1007/s00427-008-0215-2

Genomic resources for invertebrate vectors of human pathogens, and the role of VectorBase

High-throughput genome sequencing techniques have now reached vector biology with an emphasis on those species that are vectors of human pathogens. The first mosquito to be sequenced was Anopheles gambiae, the vector for Plasmodium parasites that cause malaria. Further mosquitoes have followed: Aedes aegypti (yellow fever and dengue fever vector) and Culex pipiens (lymphatic filariasis and West Nile fever). Species that are currently in sequencing include the body louse Pediculus humanus (Typhus vector), the triatomine Rhodnius prolixus (Chagas disease vector) and the tick Ixodes scapularis (Lyme disease vector). The motivations for sequencing vector genomes are to further understand vector biology, with an eye on developing new control strategies (for example novel chemical attractants or repellents) or understanding the limitations of current strategies (for example the mechanism of insecticide resistance); to analyse the mechanisms driving their evolution; and to perform an exhaustive analysis of the gene repertory. The proliferation of genomic data creates the need for efficient and accessible storage. We present VectorBase, a genomic resource centre that is both involved in the annotation of vector genomes and act as a portal for access to the genomic information ( http://www.vectorbase.org).

Effectiveness of lotions based on essential oils from aromatic plants against permethrin resistant Pediculus humanus capitis

In Argentina, field populations of the head louse Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae) have developed resistance to permethrin and other pyrethroids. Thus, the aim of this work was the development of a lotion containing essential oils from plants and an alcoholic coadjuvant to improve biological effect. Ethanol + isopropanol (1 + 1 in volume) 50% in water and ethanol 96% were taken as bases for preparation of experimental lotions containing essential oils from plants. We found that experimental lotions containing lavender, peppermint and eucalyptus oils in a 5% composition and the combination of eucalyptus and peppermint in a total concentration of 10%, dissolved in 50% ethanol + isopropanol (1 + 1) in water, showed the best knockdown effect. On the other side, lotion containing peppermint oil and eucalyptus oil (1 + 1) 10%, dissolved in ethanol 96%, showed to be as effective as the best commercial lotion now available in Argentina. Furthermore, addition of 1-dodecanol in all cases increased the effectiveness of all the experimental lotions. This difference is significantly important for 1-dodecanol concentration of 10%, reaching a toxic activity compared to the best commercial lotion available in the market.

Host‐symbiont interactions of the primary endosymbiont of human head and body lice

The first mycetome was discovered more than 340 yr ago in the human louse. Despite the remarkable biology and medical and social importance of human lice, its primary endosymbiont has eluded identification and characterization. Here, we report the host-symbiont interaction of the mycetomic bacterium of the head louse Pediculus humanus capitis and the body louse P. h. humanus. The endosymbiont represents a new bacterial lineage in the gamma-Proteobacteria. Its closest sequenced relative is Arsenophonus nasoniae, from which it differs by more than 10%. A. nasoniae is a male-killing endosymbiont of jewel wasps. Using microdissection and multiphoton confocal microscopy, we show the remarkable interaction of this bacterium with its host. This endosymbiont is unique because it occupies sequentially four different mycetomes during the development of its host, undergoes three cycles of proliferation, changes in length from 2-4 microm to more than 100 microm, and has two extracellular migrations, during one of which the endosymbionts have to outrun its host's immune cells. The host and its symbiont have evolved one of the most complex interactions: two provisional or transitory mycetomes, a main mycetome and a paired filial mycetome. Despite the close relatedness of body and head lice, differences are present in the mycetomic provisioning and the immunological response.

Serine proteinases of the human body louse (Pediculus humanus): sequence characterization and expression patterns

After the previous characterization of one trypsin gene (Try1) of the human body louse Pediculus humanus, genes encoding a second trypsin (Try2) and a chymotrypsin (Chy1) have been cloned using degenerate serine proteinase primers and 5'- and 3'-RACE, and sequenced. The deduced 259 and 267 amino acid sequences of Try2 and Chy1 show an identity of 33%-40% to trypsinogens and chymotrypsinogens of other insects. Considering previously published partial sequences, P. humanus possesses at least one Try1 gene, five variants/isoforms of Try2 and six variants/isoforms of Chy1. The genomic DNA of Try2 contains three introns and Chy1 contains five introns. Using whole mount in situ hybridization, gene expression of Try1, Try2 and Chy1 has been localized not only in the distensible anterior region of the midgut of lice but sometimes also in the area following the distensible region. The Try2 gene was always expressed at much lower levels than Try1 or Chy1. This lower expression, the constitutive expression of Try1 and Chy1 at 1, 2, 6, 12 and 24 h after feeding of adults and the regional differences have been verified in quantitative real-time PCR.

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 [1, 2]: 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.

Head lice.

Head lice.