Adult Head Lice Research Articles

Presence of the knockdown resistance (kdr) mutations in the head lice (Pediculus humanus capitis) population in the North of Iran.

Head lice infestation continues to be a major health problem worldwide. In order to solve this problem, frequent use of pediculocides has caused growing resistance among head lice population. This study aims to investigate the presence of the knockdown resistance (kdr) mutation in the head lice population in northern Iran. Adult head lice were collected from 115 infested individuals referring to the health centers in different parts of Mazandaran province, northern Iran. 38 samples were randomly selected, and Polymerase chain reaction (PCR) was used to amplify a 332-bp and ⁓ 900-bp fragment of the α-subunit of the voltage-sensitive sodium channel (VSSC) gene. According to the analysis of a 332-bp fragment of the VSSC gene, the frequency of kdr T917I mutation including homozygous susceptible (SS), heterozygous resistant (RS), and homozygous resistant (RR) were 45.83%, 12.5%, and 41.66%, respectively. The total frequency of the resistance allele was 54.16%. The results of the 900-bp fragment of the VSSC gene showed two new mutations in the IIS1-2 extracellular loop (H813P) and IIS2 (S825R) and old well-known kdr mutations (M815I-T917I-L920F). The results of Hardy-Weinberg's exact equilibrium test showed that the frequency of genotypes in the studied areas is different from expectations. Moreover, a positive inbreeding coefficient value (F is >0) was found in studied areas which indicated an excess of homozygotes. Overall, the results showed a high frequency of resistant alleles in the northern region of the country. Therefore, it is necessary to develop appropriate control programs for the treatment of pediculosis.

High mitochondrial gene diversity of Pediculus humanus capitis among children in northern Iran.

The head louse, Pediculus humanus capitis, is an obligate ectoparasite and its infestation remains a major public health issue worldwide. Determining the genetic characteristics of the existing clades is essential to identify the population structure and to develop head lice-control programs. Hence, we aimed to investigate the genetic diversity of head lice among infested individuals in northern Iran. Adult head lice were collected from 100 infested individuals referring to the health centers throughout five geographical regions in Mazandaran Province, Iran. Partial fragments of the mitochondrial cytb gene were amplified by PCR, then consequently sequenced. The results of the phylogenetic tree of collected head lice confirmed the existence of two clades, A and B, in the studied areas. Thirteen haplotypes were detected in the studied populations, of which 11 were novel haplotypes. Clade A was the dominant form and accounted for 75% of samples, while clade B included the rest. Haplotype and nucleotide diversity were 0.999 and 0.0411, respectively. Clade A and B of Pediculus humanus capitis exist among the human populations of northern Iran. We observed high genotypic diversity of this head lice.

A comprehensive survey of permethrin resistance in human head louse populations from northwest Iran: ex vivo and molecular monitoring of knockdown resistance alleles

BackgroundHead louse infestation is an important public health problem, and expanding resistance to permethrin is a major challenge to its control. The mapping and detection of pyrethroid resistance are essential to the development of appropriate treatments and ensure the effectiveness of current measures. The aim of this study was to present the phenotypic and genotypic basis of permethrin resistance and identify knockdown resistance (kdr) mutations in head louse populations in northwestern Iran.MethodsAdult head lice were collected from 1059 infested girls in Ardebil, East Azerbaijan, West Azerbaijan and Zanjan Provinces, northwestern Iran. The toxicity of permethrin and the possible synergistic effect of piperonyl butoxide (PBO) on this toxicity were assessed using bioassays. Fragments of voltage-sensitive sodium channels (vssc) and cytochrome b (cytb) genes were amplified and analyzed for the detection of knockdown resistance (kdr) mutations and mitochondrial groups. Moreover, genotypes of the two hot spot regions of the vssc gene were determined by melting curve analysis of amplicons.ResultsA total of 1450 adult head lice were collected during 2016–2021. Live lice were exposed to a dose of 1% permethrin for 12 h, and the median lethal time (LT50) and time to achieve 90% mortality (LT90) were determined to be 6 and 14.8 h, respectively. Topical application of 2 and 16 ng permethrin per louse resulted in 25% and 42.11% mortality, respectively. Pre-exposure of samples to 3% piperonyl butoxide had no synergistic effect on the effects of permethrin. Analysis of the 774-bp vssc gene fragment showed the presence of the M815I, T917I and L920F mutations, wild-type and T917I mutation, in 91.6%, 4.2% and 4.2% of samples, respectively. Investigation of the mitochondrial cytb gene demonstrated the predominance of clade B. The frequency of domain II segment 4 (S4)-S5 kdr genotypes in mitochondrial groups was identical, and heterozygotes were present in 93.5% of samples. A significant difference was detected in the frequency of domain IIS1-S3 kdr genotypes, and the frequency of resistant alleles and heterozygotes was higher in clade B than in clade A.ConclusionsThe presence of kdr mutations in the vssc gene and the non-synergist effect of PBO indicate that pyrethroid target site insensitivity is the main resistance mechanism. This phenomenon and the high frequency of resistant alleles necessitate that new pediculosis management programs be developed. Further studies need to be conducted to identify all factors contributing this resistance and to develop alternative pediculicides.Graphical

Pyrethroid-linked resistance allelic mutations by molecular analysis in wild human head louse (Phthiraptera: Pediculidae) populations from schoolgirls of South Iran

BackgroundHuman head louse, Pediculus humanus capitis De Geer, 1767 (Anoplura: Pediculidae), is one of the most frequent ectoparasites infesting Homo sapiens worldwide. Reduced sensitivity to treatment due to genetic mutations, in particular knockdown resistance (kdr) (or target site insensitivity) allele, has led to this infestation prevalence. Molecular characterization of this resistance has a crucial impact on selecting appropriate treatment protocol. The aim of this study was to investigate kdr gene mutations on voltage-sensitive sodium channel (VSSC) among wild head lice samples from Fars province, southern Iran. MethodsHead lice were collected using plastic detection combs on girls enrolled in public schools from 10 counties in Fars province. The specimens were screened in 10 pools (each pool per county containing 35 specimens), with three pools (30%) being positive. Following species identification with valid entomological keys, 350 (68%) out of 514 randomly collected adult head lice were analyzed after their somatic genomic DNA extraction using Sinaclon kit. Samples were investigated by polymerase chain reactions (PCR), and the amplicon was subsequently sequenced. ResultsSequence analysis showed that the sodium channel genes in the pooled ectoparasites had two intron and three exon regions. Single (L840F), double (I836L, E837K), and triple novel point mutations (V875L, Q876P, S879V); the last involving two concomitant allelic substitutions; were discovered in the second and third exon regions of head louse DNA on chromosome II from three (30%) counties. Other exon or intron regions remained non-mutated from the remaining seven counties. ConclusionsThe detection of six amino acid substitutions from 30% of examined head lice among infested schoolgirls reveal that mutants are minutely developing. These findings provide further incentive to recapitulate the legitimacy of current control measures and resolve dynamics of resistance in human head louse populations.

COMPARISON BETWEEN THE EFFECT OF TITANIUM DIOXIDE NANOPARTICLES AND IVERMECTIN ON HEAD LICE

Head lice cause social problems for patients as embarrassment, inflammation, skin irritationand secondary bacterial infection. Treating head lice is difficult because of development of resistanceto drug. In this study, our aim was to evaluate the effect of titanium dioxide, Ivermectinand Ivermectin-loaded on Titanium dioxide nanoparticles on head lice in vitro. This study wasconducted on 50 patients infected with head lice from Beni Suef Governorate. These patientswere of all age groups and both sexes.Patients were 13 males and 37 females, with ages ranged from 5 to72years (26.84±19.3). Theywere 34 rural residents, and 16 urban ones, 37 were at a low socioeconomic level and 13 at amoderate socioeconomic one. Number of family members ranged from (3 to 11) with an averageof (6.42±1.9).The results showed that mortality rate for topical Ivermectin (0.2% & 0.5%) was 86% & 94%,respectively, against adult head lice, while 88% and 94%, respectively, against nymphs.Regarding the effect of Titanium dioxide, the percentage mortality effects of Titanium dioxidewere 34, 58, & 100% at (2, 6, & 10 mg/L), respectively, against adult head lice, while Titaniumdioxide mortality rate was 40, 68 & 96% at (2, 6 &10 mg/L), respectively, against nymphs.

Diversity of mitochondrial genes and predominance of Clade B in different head lice populations in the northwest of Iran

BackgroundThe head louse, Pediculus humanus capitis, is the most important ectoparasite causing many health problems. Several linkages are presented for this parasite, each representing a particular geographical distribution, prevalence rate, vector competence, susceptibility to pediculicides, and infestation rate. Determining the genetic nature of these linkages is necessary to identify the population structure and also to develop and monitor control programmes against head lice. This study was designed to analyse cox1 and cytb genes and determine the mitochondrial clades in head lice populations in the northwest of Iran.MethodsAdult head lice were collected from infested females of Ardabil, East and West Azerbaijan, and Zanjan Provinces from 2016 to 2018. Partial fragments of the mitochondrial genes cox1 and cytb were amplified by PCR and some of the amplicons were sequenced. All confirmed sequences were analysed, and the frequency of each mitochondrial clade was determined in the studied areas.ResultsA total of 6410 females were clinically examined, and 897 adult head lice were collected from 562 infested cases. Genomic DNA was extracted from 417 samples, and fragments of cox1 and cytb genes were amplified in 348 individuals. Analysis of the 116 sequences showed the 632-bp and 495-bp fragments for cox1 and cytb genes, respectively. The nucleotide and haplotype diversities of cytb and cox1 genes were 0.02261 and 0.589 and 0.01443 and 0.424, respectively. Sequence analysis indicated 6 haplotypes clustered in two clades, A and B. The relative prevalence of clade B was 73% for cytb and 82% for cox1 gene. Haplotypes of clade B were found in all the studied areas, while those of clade A were observed only in rural and suburban areas.ConclusionsTo our knowledge, this is the first study investigated deeply the field populations of Pediculus and documented two clades in the Middle East. The considerable prevalence of pediculosis in the studied areas requires authorities’ attention to establish effective control and preventive measures. Given the role of cytb in monitoring population groups, application of this marker is suggested for future epigenetic studies to evaluate the factors affecting the abundance of these clades.

Arrestant Effect of Human Scalp Components on Head Louse (Phthiraptera: Pediculidae) Behavior.

Relevant evidence has shown that parasites process host-related information using chemical, visual, tactile, or auditory cues. However, the cues that are involved in the host-parasite interaction between Pediculus humanus capitis (De Geer 1767) and humans have not been identified yet. In this work, we studied the effect of human scalp components on the behavior of adult head lice. Filter paper segments were rubbed on volunteers' scalps and then placed in the experimental arena, where adult head lice were individually tested. The movement of the insects was recorded for each arena using the software EthoVision. Average movement parameters were calculated for the treatments in the bioassays such as total distance, velocity, number of times a head louse crossed between zones of the arena, and time in each zone of the arena. We found that scalp components induced head lice to decrease average locomotor activity and to remain arrested on the treated paper. The effect of the ageing of human scalp samples in the response of head lice was not statistically significant (i.e., human scalp samples of 4, 18, 40, and 60 h of ageing did not elicit a significant change in head louse behavior). When we analyzed the effect of the sex in the response of head lice to human scalp samples, males demonstrated significant differences. Our results showed for the first time the effect of host components conditioning head lice behavior. We discuss the role of these components in the dynamic of head lice infestation.

Effect of Environmental Conditions and Toxic Compounds on the Locomotor Activity of Pediculus humanus capitis (Phthiraptera: Pediculidae).

In this work, we evaluated the effect of environmental variables such as temperature, humidity, and light on the locomotor activity of Pediculus humanus capitis. In addition, we used selected conditions of temperature, humidity, and light to study the effects of cypermethrin and N,N-diethyl-3-methylbenzamide (DEET) on the locomotor activity of head lice. Head lice increased their locomotor activity in an arena at 30°C compared with activity at 20°C. When we tested the influence of the humidity level, the locomotor activity of head lice showed no significant differences related to humidity level, both at 30°C and 20°C. Concerning light influence, we observed that the higher the intensity of light, the slower the movement of head lice. We also demonstrated that sublethal doses of toxics may alter locomotor activity in adults of head lice. Sublethal doses of cypermethrin induced hyperactivated responses in adult head lice. Sublethal doses of DEET evocated hypoactivated responses in head lice. The observation of stereotyped behavior in head lice elicited by toxic compounds proved that measuring locomotor activity in an experimental set-up where environmental conditions are controlled would be appropriate to evaluate compounds of biological importance, such as molecules involved in the host-parasite interaction and intraspecific relationships.

Treatment of head lice (Pediculus humanus capitis) infestation: is regular combing alone with a special detection comb effective at all levels?

Head lice infestation (HLI) caused by Pediculus humanus capitis has been a public health problem worldwide. Specially designed combs are used to identify head lice, while anti-lice products are applied on the scalp for treatment. In the present study, we aimed to test whether combing only by precision detection comb (PDC) or metal pin comb (MPC) could be effective alternatives to the use of anti-lice products in children. A total of 560 children from two rural schools in Turkey were screened. In the PDC trial, children were combed every second day for 14 days, while in the MPC trial, combing was performed once in every four days for 15 days. Children were divided into two groups (dry combing and wet combing) for both trials and results were compared. The results showed no significant differences between dry and wet combing strategies for both combs for the removal of head lice (p > 0.05). The number of adult head lice declined significantly on each subsequent combing day in both approaches, except on day 15 in the MPC trial. In the end, no louse was found in 54.1 and 48.9% of children in the PDC and MPC trials, respectively. Since family members of infested children were not available, they were not checked for HLI. Four times combing within 2 weeks with MPC combs was found effective for both treatment of low HLI and prevention of heavy HLI. In conclusion, regular combing by special combs decreases HLI level in children and is safely applicable as long-term treatment.

Severe Head Lice Infestation in an Andean Mummy of Arica, Chile

Pediculus humanus capitis is an ancient human parasite, probably inherited from pre-hominid times. Infestation appears as a recurrent health problem throughout history, including in pre-Columbian populations. Here, we describe and discuss the occurrence of pre-Columbian pediculosis in the Andean region of the Atacama Desert. Using a light microscope and scanning electron microscopy, we studied a highly infested Maitas Chiribaya mummy from Arica in northern Chile dating to 670-990 calibrated years A.D. The scalp and hair of the mummy were almost completely covered by nits and adult head lice. Low- and high-vacuum scanning electron microscopy revealed a well-preserved morphology of the eggs. In addition, the excellent preservation of the nearly 1,000-yr-old adult head lice allowed us to observe and characterize the head, antennae, thorax, abdomen, and legs. Leg segmentation, abdominal spiracles, and sexual dimorphism also were clearly observed. The preservation of the ectoparasites allowed us to examine the micromorphology using scanning electron microscopy; the opercula, aeropyles, and spiracles were clearly visible. This case study provides strong evidence that head lice were a common nuisance for Andean farmers and herders. Head lice are transmitted by direct head-to-head contact; thus, this ancient farmer and herder was potentially infesting other people. The present study contributes to the body of research focusing on lice in ancient populations.

Bartonella quintanain head louse nits

The body louse is the principal vector of Bartonella quintana, the causative organism of trench fever, but B. quintana DNA has also been detected in adult head lice. Because there are no characteristics that distinguish the body louse from the head louse, we decided to test head louse nits collected from a homeless man for the presence of B. quintana DNA. All of the sampled nits tested positive by real-time PCR, and intergenic spacer region (ITS) gene sequences shared 100% similarity to the corresponding ITS fragment of the genome of B. quintana. The role of the head louse in the maintenance and transmission of B. quintana remains to be determined.

Ex Vivo Development of Eggs from Head Lice (Pediculus humanus capitis)

Background: Data on ovicidal activity of pediculicides are essential to determine the efficacy of commercial products, and to define application schemes. We present an adaptation of historical methods for rearing head lice, and describe their development ex vivo. Methods: Adult head lice were collected and fed on volunteers to obtain fertile eggs of known age. Two methods of feeding were applied: interval feeding (performed every 8-12 hours), and continuous feeding (placing lice in a round Plexiglas receptacle, closed with gauze attached to the skin). Eggs were incubated at 25-28,6°C and 51,8% - 69,3% relative humidity. The following outcome measures were used: appearance of eye spot; presence of embryonic structures; presence of embryonic movements; and hatching. A total of 340 eggs were obtained by continuous feeding. Of these, 205 were examined daily. The remaining 135 eggs and those obtained by interval feeding (n=159) were observed once, to confirm hatching status. Results: Eye spots of the embryos started to appear 6 days after oviposition (median = 7 days), and embryonic movements were first seen 9 days after oviposition (median =11 days). Interval feeding of head lice revealed a hatch rate of 10,7% (17/159), as compared to a hatch rate of 80,9% (275/340) achieved with continuous feeding. Hatching started 9 days after oviposition (median = 12 days). Skin irritation (papular rash; moderate to severe itching) appeared after continuous feeding of adult lice on volunteers. Conclusions: Continuous feeding of head lice on a human host is a suitable approach to obtain head lice eggs for ovicidal testing. The method is simple and cheap, offers conditions similar to the natural habitat, and hatch rates are high. However, side effects on volunteers are considerable.