Molecular Surveillance of Pyrethroid Resistance Kdr Alleles T917I and L920F in Head and Body Lice from Nigeria

Abstract

Pediculosis produced by the presence of the human head louse (Pediculus humanus capitis DeGeer, 1767) and the body louse (Pediculus humanus humanus L., 1758) remains a neglected tropical disease in Nigeria, where permethrin-based pediculicides are widely used. However, the resistance status of lice populations has not been previously assessed. Knockdown resistance (kdr) to pyrethroids is primarily driven by two mutations—T917I and L920F—in the voltage-sensitive sodium channel (VSSC) gene. This study investigated the presence of these mutations in 85 head and body lice collected from school-age children in two settlements in Nigeria. The T917I mutation was detected in head lice at frequencies ranging from 21% to 76%, and in body lice from 10% to 95%, with significant variation between sites and louse types. Remarkably, all lice examined carried the L920F mutation, regardless of T917I genotype, a pattern not previously reported in body lice. These findings suggest that pyrethroid resistance is well established or under active selection in the study populations. This is the first report of kdr mutations in human lice from Nigeria and highlights the urgent need for resistance monitoring programs. Early genetic surveillance of these mutations can inform treatment strategies and help prevent widespread resistance in lice populations, preserving the efficacy of available pediculicides.

1. Introduction

Lice have been associated with humans for centuries, likely tracing back to our pre-hominid ancestors in Africa [1]. These highly specialized blood-sucking insects complete their entire life cycle on their host. The head louse, Pediculus humanus capitis, primarily inhabits the scalp, while the body louse, Pediculus humanus humanus, lives and lays its eggs on the host’s clothing. Although these two ecotypes are morphologically similar, they differ in ecology, immunology, and nutritional habits [2]. Additionally, it has been suggested that body lice evolved from head lice when humans began wearing clothing around 170,000 years ago [3]. Head louse infestations, known as pediculosis, are common worldwide, particularly affecting school-aged children. Recently, the World Health Organization (WHO) added head lice to the list of neglected tropical diseases (NTDs) [4]. The spread of head lice primarily occurs through direct head-to-head contact and is significantly influenced by social and behavioral factors [5]. Individuals with head lice may experience various symptoms, including irritation, itching, and secondary bacterial infections resulting from intense scratching [6]. In contrast, body louse infestations are often linked to overcrowding and poor sanitation, typically seen in the living conditions of the homeless and refugees [7]. Symptoms of body lice infestations can include fever, headaches, a diffuse rash, fatigue, and muscle pain. Body lice can also transmit several pathogenic bacteria of medical importance, including Rickettsia prowazekii, the causative agent of typhus; Borrelia recurrentis, which causes relapsing fever; and Bartonella quintana, responsible for trench fever [8]. In contrast, while head lice can harbor human pathogens, it is thought that their robust immune response—compared to that of body lice—prevents bacterial proliferation, making head lice unsuitable as vectors [9].

Over-the-counter (OTC) topical products remain the preferred method for treating lice, with estimated annual pediculicide sales in the United States exceeding $200 million [10]. Pyrethroid-based pediculicides represent the largest segment of the global market, with permethrin demonstrating the highest utilization rate among active ingredients. This pyrethroid is regarded as an effective insecticide due to their low toxicity on dermal, primary skin, and eye irritation on mammals. Continuous and intensive use of this class of insecticide has led to the development of resistance, ultimately hindering head louse control strategies in several countries, including Denmark, the UK, France, Japan, Argentina, the USA, Russia, Chile, Honduras, and Iran [11,12,13,14,15,16,17,18,19,20]. Concerning body lice control, permethrin resistance was reported in France and Russia [17,21]. Pyrethroid resistance is likely the most significant factor contributing to the worldwide increase in head lice infestations. Lice with knockdown resistance (kdr) to pyrethroids have single-nucleotide polymorphisms (SNPs) in the voltage-sensitive sodium channel (VSSC) gene, reducing the sensitivity of their nerve cells [2]. Three-point mutations, identified as M815I, T917I, and L920F, are responsible for the modification mechanism at this site of action related to pyrethroid resistance [22]. Experimental evidence indicates that the T917I mutation, occurring independently or synergistically with other mutations, results in the complete loss of permethrin sensitivity. This mutation may resemblance to the super-kdr trait reported in other insect species, a genetic determinant of near-absolute permethrin resistance. Therefore, this point mutation can serve as a molecular biomarker for detecting resistance [23].

In sub-Saharan Africa, the scarcity of resources and trained health personnel leads to the neglect of minor parasitic diseases, such as pediculosis. In Nigeria, pediculosis is a common public health problem with prevalence values up to 45% [24]. A recent study in Port Harcourt found that pediculosis among children increased from 0.7% to 17% over a decade [25,26]. The variation in prevalence may be due to the ineffectiveness of treatments used for head lice infestations. Permethrin is the primary treatment option to pediculosis due to its cost-effectiveness and acceptance in many Nigerian communities [24]. There is no available prevalence and control information regarding body lice in Nigeria. Despite the treatments employed to control human lice, the insecticide resistance status of head lice in Nigeria has not been evaluated. The aim of this study was to investigate the occurrence of sodium channel mutations T917I and L920F in head and body lice collected from two urban regions in Nigeria.

2. Materials and Methods

2.1. Ethical Approval

Lice sampling is a non-invasive procedure conducted in accordance with the protocols outlined in the Declaration of Helsinki by the World Medical Association for collecting non-invasive samples from humans. Participants and their representatives were informed about the study’s purpose. Before being examined for the presence of lice on their heads or clothing, verbal consent was obtained from each volunteer in the presence of their representatives. Only children with a signed legal custodian’s consent were screened for louse removal. All lice specimens were collected by trained health professionals experienced in parasitological sampling to ensure proper identification and minimize discomfort to participants. The collections were performed under hygienic conditions, following local health regulations and institutional ethical guidelines. No chemical or mechanical treatment was applied beyond what is routinely used for lice removal.

2.2. Study Location and Louse Sampling

To collect head lice, each child’s hair was first brushed with a regular hairbrush. Next, the entire scalp was carefully combed using a fine-toothed louse comb for 5 to 10 min. For body lice, any visible lice were removed from the clothing using forceps.

A total of 136 school-age (7–14-year-old) children volunteers in two cities; Yunusari (13.185° N, 11.616° E) and Maiduguri (11.831° N, 13.151° E) in Nigeria were examined for human lice infestation between July and November 2022 (Figure 1). The collected lice specimens were placed in pre-labelled Eppendorf tubes containing absolute ethanol and transported to the Entomology Laboratory, Parasitology, Division, NVRI Vom, Nigeria and stored at −20 °C until analysis. Under a stereoscopic zoom microscope, nymphs, adult females, and male lice were classified. The identification of lice was performed using taxonomic keys [27] and were photographed with a Sony 5X optical zoom camera.

2.3. Pediculicides and Lice Treatment Methods

Information about lice treatment methods used in the areas was collected from 51 parents or guardians of the volunteers using a structured questionnaire. In addition, a survey of 23 pharmacies and 30 patent medicine stores in the study areas was conducted to identify the availability of recommended pediculicides in both areas. Where available, the active ingredients/chemical components of the products used for human lice were recorded.

2.4. DNA Extraction

Adult lice used for DNA extraction were first decontaminated by washing them in sterile phosphate-buffered saline (PBS) and then drying them with a sterile paper towel. Each louse or nit was placed in a 1.5 mL microtube, where it was cut into small pieces using the tip of a sterile hypodermic needle under a stereomicroscope. The samples were then manually homogenized with a plastic pestle. Genomic DNA was extracted from individual louse or nit specimens using the Quick-DNA™ Miniprep plus Kit (Zymo Research, Irvine, CA, USA), following the manufacturer’s instructions. The DNA was eluted into 60 μL of elution buffer and stored at −20 °C until analysis.

2.5. Amplification of the Knockdown Resistance (Kdr) Gene Fragment by Conventional PCR and Sequencing

To detect the presence of kdr mutations in DNA obtained from adult lice or nits, conventional PCR was performed to amplify a 332-bp fragment of the α-subunit of the voltage-sensitive sodium channel (VSSC) gene in the specimens. The primers used for the PCR amplification were 5′-AAATCGTGGCCAACGTTAAA-3′ (sense) and 5′-TGAATCCATTCACCGCATAA-3′ (antisense) as described by Durand et al. [13].

The PCR mixture included 12.5 μL of 2X Master Mix (New England Biolabs Inc., Ipswich, MA, USA), 0.5 μL of each 10 mM primer, 5 μL of DNA template, and 6.5 μL of nuclease-free water (BioConcept, Allschwil, Switzerland), resulting in a total volume of 25 μL. The amplification cycling conditions were set to: initial denaturation at 94 °C for 30 s, followed by 38 cycles consisting of denaturation at 94 °C for 15 s, annealing at 55 °C for 45 s, and extension at 68 °C for 1 min, and concluding with a final extension at 68 °C for 7 min. The PCR reactions were conducted using a GeneAMP PCR System 9700 (Applied Biosystems, Foster City, CA, USA).

The amplified products were evaluated by electrophoresis on a 1.2% agarose gel stained with SafeView (Applied Biological Materials, Richmond, BC, Canada) at 95 V for 30 min. The results were visualized on a Blue Light Trans-illuminator (Cleaver Scientific, Rugby, UK) in comparison to a 100-bp molecular ladder (New England Biolabs Inc., Ipswich, MA, USA).

2.6. Detection of Kdr Alleles Using PCR-RFLP (Restriction Fragment Length Polymorphism)

To investigate the presence of single SNPs associated with the kdr mutations in human lice samples using PCR-RFLP, we treated the amplified PCR products with the SspI enzyme in separate digestion reactions. Each reaction was conducted in a final volume of 25 μL, consisting of 2.5 μL of 10× NEBuffer (New England Biolabs Inc., Ipswich, MA, USA), 0.5 μL of SspI enzyme (New England Biolabs Inc., Ipswich, MA, USA), 10 μL of PCR amplicon, and 12 μL of nuclease-free water (BioConcept, Allschwil, Switzerland). The reaction mixture was incubated at 37 °C for 30 min, followed by an inactivation step at 65 °C for 20 min.

The digested products were then subjected to electrophoresis on a 2.0% agarose gel, which was stained with SafeView, at 80 volts for 1 h. The gels were visualized using a blue light trans-illuminator. We determined the pattern for resistant or susceptible genotypes of the T917I of both head and body lice as follows: homozygous-susceptible lice (SS) were identified by a single fragment of 332 bp; heterozygous susceptible lice (SR) presented three fragments of 332, 261, and 71 bp; and homozygous-resistant lice (RR) exhibited two fragments of 261 and 71 bp [13].

Results of the PCR-RFLPs were validated by sequencing the control fragment directly amplified with the used primers, encompassing the mutations T917I and L920F under study. In addition, sequencing detected the L920F mutation, which was not possible with the PCR-RFLP method.

All the amplicons from the 85 studied individuals were Sanger-sequenced bi-directionally at The Centre of Genomic Technology, The Hebrew University, Jerusalem, Israel, using the same PCR primers used previously. The obtained sequences were then compared to the wild-type sequence (accession number AY191156.1 in Genbank) in the search of two single-nucleotide polymorphism (SNPs) associated with kdr mutations, T917I and L920F.

2.7. Nucleotide Sequencing Analysis for SNPs

DNA sequencing data was checked manually. All the confirmed sequences were aligned with the wild type (AY191156.1, GenBank) nucleotide sequence to determine the single point mutations T917I and L920F associated with kdr in human lice. This procedure followed the method through/slowest (overlap 25, overlap identity 80, gap open/extend penalty 18, mismatch score 18, match score 5) implemented in Geneious R11 software.

3. Results

3.1. Kdr-Allele Frequency

The kdr gene fragment of 332-bp size was amplified from each of the 85 human lice specimens examined in this study. To ensure a broad representation of kdr mutations at the studied sites, only one or two lice were collected from each host. The presence of the T917I mutation was detected in all of the tested samples (

Table 1. Frequency of the kdr-like allele (T917I) in human lice collected in Nigeria.

Population	No. of Lice Analyzed (No. of Affected Subjects)	Genotype a			Resistance Allele Frequency (%)	H-W b (χ2)	FIS c
		S/S	R/S	R/R
Maiduguri	HL 46 (35)	3 (6.52)	16 (34.78)	27 (58.70)	76.08	0.0897	0.055
	BL 22 (22)	1 (4.54)	0 (0)	21 (95.46)	95.45	22 *	1
Yunusari	HL 12 (10)	9 (75)	1 (8.33)	2 (16.67)	20.83	6.702 *	0.766
	BL 5 (5)	4 (80)	1 (20)	0 (0)	10	0.0617	-
Total	85 (72)	17 (20)	18 (21.18)	50 (58.82)	69.41	21.361 *	0.232

Abbreviation: ^a S and R are susceptible and resistant alleles. Between brackets are the percentages of each genotype proportion. HL: head lice, BL: body lice. ^b Field populations were tested for the Hardy–Weinberg equilibrium by the χ² (p < 0.05; df = 2; χ² = 3.84). ^c F_IS values > 0 indicate heterozygote deficiency, whereas F_IS values < 0 indicate heterozygote excess. * Values that are statistically significant at p < 0.05. Significance level indicates rejection of the null hypothesis F_IS = 0 at p < 0.05.

). The percentage of susceptible, heterozygous and homozygous-resistant individuals exhibiting the T917I mutation is shown in Table 1.

Considering the study locations, of the 68 samples from Maiduguri, 48 (70.6%) were homozygous-resistant, 16 (23.5%) were heterozygous, and 4 (5.9%) were homozygous-susceptible. In contrast, the samples from Yunusari showed a prevalence of homozygous susceptibility at 76.4% (n = 13), with only 2 (11.8%) being either homozygous-resistant or heterozygous (Table 1). Overall, 21.2% (n = 18) of the tested lice carried the heterozygous gene, while 50 (59.0%) possessed the homozygous-resistant gene, resulting in a global frequency of the T917I mutation of 69.41%.

In the study of head lice populations, Maiduguri had an average resistance allele frequency of 76.0%, while Yunusari had a frequency of 21.0% (Table 1). Considering that the kdr mutation is only partially recessive and is functionally more relevant in the homozygous state, the percentage of individuals with the resistant genotype (RR) was 59.0% in Maiduguri and 17.0% in Yunusari. Similarly, for body lice, Maiduguri exhibited a resistance allele frequency of 95.0%, whereas Yunusari showed a frequency of 10.0%. Notably, 21 of the 22 analyzed body lice from Maiduguri were homozygous-resistant, while the remaining lice were homozygous-susceptible. In contrast, 80.0% of the body lice from Yunusari were found to be homozygous-susceptible.

3.2. Sequencing Analysis

The nucleotide sequences obtained from head and body lice in this study were aligned and compared to the insecticide-susceptible genotype of Pediculus humanus capitis (accession no. AY191156.1) in GenBank. The homozygous-resistant sequences from both head and body lice indicated that T917I was caused by a C→T substitution, which resulted in a change from Threonine (ACA) to Isoleucine (ATA). Furthermore, the mutation identified as L920F was present in all homozygous-resistant sequences and was linked to a C→T nucleotide substitution that led to a predicted change from Leucine (CTT) to Phenylalanine (TTT) (Figure 2A,B). The nucleotide sequences of the knockdown resistance (kdr) alleles detected in this study were submitted to GenBank under the following accession numbers: OR607358−OR607635 for head lice and OR603358−OR607369 for body lice.

3.3. Survey of Pediculicides

A survey conducted in several pharmacies and drug shops within the study areas revealed that there are no specific pediculicides available for the treatment of human lice, either as over-the-counter (OTC) treatments or as prescription products. Instead, parents and guardians of affected individuals reported using homemade remedies for lice treatment rather than visiting hospitals for expert advice.

In Yunusari, common preparations used for lice infestation included Rambo™ (a domestic multi-purpose insecticide containing 0.6% permethrin), Mectizan™ (Ivermectin), and several local formulations with unknown active ingredients. Respondents in Maiduguri mentioned using Acneaway™ cream (which contains triamcinolone, an antifungal, antibacterial agent, and corticosteroid), Mectizan™ (Ivermectin), as well as local formulations of organophosphate and organochlorine, along with Rambo™ (0.6% permethrin) for treating lice.

4. Discussion

In resource-limited countries like Nigeria, pediculosis often does not receive adequate attention due to the overwhelming burden of more serious health issues, such as malaria, HIV/AIDS, typhoid, and poliomyelitis. This lack of focus on pediculosis has contributed to its classification as a neglected tropical disease. In response to this oversight, the World Health Organization has prioritized pediculosis in its list of neglected tropical diseases [4]. Addressing pediculosis is essential not only for improving individual health but also for enhancing overall public health outcomes in these regions. The identification of one or two fragments following digestion with the SspI restriction enzyme was a useful diagnostic biomarker for detecting mutations associated with pyrethroid resistance in head and body lice found in Nigeria. This study presents the first report on pyrethroid resistance in human lice from two regions of Nigeria, utilizing PCR-RFLP and nucleotide sequence analysis. In order to improve head lice treatment outcomes and prevent the development of widespread occurrence of resistant population, there is a need for surveillance of the kdr genes to guide in the formulation of cost-effective control measures [28]. Previous studies have demonstrated the utility of the combination of PCR-RFLP by using the SspI restriction enzyme to determine the presence of kdr mutation genes [13,17,18].

According to the current analysis, a significant proportion (80%) of human head and body lice in Nigeria were found to carry the kdr mutations T917I and L920F. Our findings regarding head lice align with a global kdr map of head louse populations from 14 countries reported an overall frequency of the resistance allele ranging from 29% to 100% [29]. According to Fox et al. [28], 70% of the head lice worldwide harbor homozygous resistance alleles. The considerable variation in resistance allele frequency suggests geographical differences that may be influenced by the use of various pyrethroid formulations and inappropriate application quantities for treating pediculosis, resulting in selective pressure. It has been noted that high levels of genetic exchange, combined with increased selection pressure and the overuse or misuse of insecticides, can lead to the emergence of resistant species [15].

Analysis of the nucleotide sequence of the kdr gene in Nigerian head and body lice revealed two-point mutations at the T917 and L920 loci. These mutations result in the predicted substitution of amino acids: Thr (ACA) is replaced by Ile (ATA), and Leu (CTT) is replaced by Phe (TTT). Notably, the mutation at the T917 locus has been implicated in the development of pyrethroid resistance [22]. These predicted amino acid substitutions might compromise the integrity of the nerve cell membrane, thereby diminishing the effectiveness of insecticides on the nervous system, which leads to knockdown resistance in the insects [10]. Pyrethroid resistance has been linked to three-point mutations that cause amino acid substitutions at the M815I, T917I, and L920F loci. Analysis of nucleotides and protein sequences indicated that the Nigerian lice specimens carried the T917I and L920F mutations. Both head and body lice examined in this study exhibited these mutations. This marks the first report of kdr-like alleles in body lice.

Previous studies have shown that in head lice, the T917I and L920F mutations often coexist as a haplotype, likely playing a synergistic role in enhancing pyrethroid resistance [22]. Interestingly, all the lice studied displayed the resistant phenotype L920F. This indicates that regardless of the presence of the T917I mutation, the L920F mutation was consistently found. This unexpected finding has only been reported in 40% of head lice collected from Egypt and in a single individual from Thailand [30]. However, no previous reports of this pattern were found in body lice worldwide. It has been reported that T917I mutation alone is sufficient to confer insecticide resistance and is a good representative biomarker of pyrethroid resistance in head lice [15,16,23,29,31]. Thus, the intensive and continuous use of pyrethroids has led to the development of resistance in human lice population worldwide [28]. Recently, a meta-analysis showed that permethrin effectiveness decreased from 97% to 15% in association with an increase of permethrin resistance ranging from 33% (pre-2004) to 82% (post-2015) [32].

The results from the two study areas in Nigeria showed that the frequency of kdr resistance allele was higher in head and body lice specimens obtained from Maiduguri than those from Yunusari. In particular, either head or body lice from Maiduguri showed a significant deficiency of heterozygotes suggesting that the pyrethroid resistance is strongly established. Similarly, other authors reported this same pattern in head lice from France and Argentina [15,33]. They reported that >85% of the head lice had homozygous kdr-type mutations, suggesting that the evolution of this phenomenon is not recent but strongly established and almost in fixation. On the other hand, head and body lice from Yunusari showed a very low resistance allele frequency with values of 21 and 10%, respectively. This indicates that they are still susceptible to pyrethroids. These differences may be attributed to the different lice treatment methods practiced in the two study areas.

Our investigation into the lice treatment practices adopted by parents and guardians in the study areas reveals that there is no standardized method for treating human lice infestations. While similar preparations are used in both regions, there is no consistent procedure for applying these treatments. Variations exist in the method of application, duration, frequency, quantity, and formulation of the products. Typically, parents first attempt to treat lice infestations using homemade remedies that often include combinations of local herbs. If these are ineffective, they will then turn to general-purpose chemical products such as Rambo^® and Mectizan^®. This aligns with previous reports indicating that residents of resource-limited communities frequently utilize a variety of natural or household products to manage head lice infestations, even when commercial pharmaceutical options are available, primarily due to financial constraints [28]. In addition to financial limitations, many parents interviewed do not view lice infestations as a serious health issue and believe that children will naturally outgrow the condition with age.

Additionally, the majority of the commercial chemical products mentioned by the respondents in this study are officially approved as pediculicides. Most respondents were unaware of the active ingredients in the local pediculicides they have been using. Consequently, even if these local products contain the recommended active ingredients, the treatment regimen may not deliver the appropriate curative dosage. This could expose lice to sub-therapeutic levels of the pediculicide, thereby increasing selective pressure that contributes to the spread of resistance [34,35]. We proposed two hypotheses to explain the significant differences in permethrin resistance observed in human lice in Nigeria: (1) variations in the active ingredients of homemade preparations may have resulted in exposure to pyrethroids in Maiduguri, while those in Yunusari may have been exposed to non-pyrethroid active ingredients; and (2) the differences in the use and levels of exposure to insecticides—whether for domestic or agricultural purposes—among individuals in the two study areas may have contributed to varying levels of selective pressure, leading to the development of pyrethroid resistance. Therefore, the inconsistency and lack of adherence to standard application methods for pediculicides may explain the overall variation in resistant alleles among the lice populations in these two study areas. Further research is necessary to clarify these findings.

The use of Mectizan^® (ivermectin), an oral parasiticide commonly employed for the treatment and prevention of Guinea worm infections in Nigeria, exemplifies a misunderstanding in the treatment of pediculosis. Fortunately, there are reports confirming the effectiveness of ivermectin in treating head lice in various countries [8]. As a result, both oral and topical formulations of ivermectin have gained favourable attention due to their low toxicity, broad spectrum of action, and cost-effectiveness [36].

Permethrin resistance in head and body lice is primarily associated with kdr mutations and is influenced by the intensity and frequency of control measures used to manage pediculosis. Therefore, different strategies should be adopted based on the level of resistance in Nigerian human louse populations. For instance, in Yunusari, where the biomarker of permethrin resistance possesses a low frequency, the use of pyrethroids should continue, ideally alongside resistance monitoring programs. Conversely, in Maiduguri, where lice exhibited high frequency of the T917I allele, it is advisable to stop using pyrethroids and switch to products that operate through different mechanisms such as ivermectin. To establish an effective resistance management program, it is crucial to detect early signs of insecticide resistance while simultaneously promoting preventive measures to curb its spread. Although traditional toxicological bioassays are highly recommended for early resistance detection, they can be impractical and difficult to implement operationally.

To address the limitations identified, the PCR-restriction fragment length polymorphism (RFLP) method utilized in this study has proven to be a reliable, cost-effective, and reproducible assay for accurately genotyping individual head lice with the resistance-conferring T917I mutation. The findings underscore the urgent need for enhanced basic and applied research in Nigeria, particularly the establishment of comprehensive regional health surveillance programs aimed at monitoring and controlling human lice populations. Critical to these programs is the implementation of regular testing initiatives to detect and assess resistance levels among lice, which might facilitate timely interventions and inform treatment strategies. Moreover, there is an immediate need to raise awareness among the general public and healthcare providers regarding the dangers of using unregulated or harmful products for treating human pediculosis. By adopting this recommendation, it can significantly reduce unnecessary pesticide exposure among children, thereby mitigating both acute and chronic intoxications. Enhanced education efforts, combined with monitoring and testing programs, will play a vital role in promoting safer and more effective lice management practices.

5. Conclusions

This study highlights the presence of the T917I and L920F kdr alleles in both human head and body lice collected from school-age children in Nigeria. The findings reveal a high prevalence of pyrethroid-resistant alleles in lice populations from Maiduguri, underscoring the urgent need to address the inappropriate use of various treatment preparations. The reliance on local remedies of uncertain efficacy and the utilization of products designed for agricultural or domestic use not only compromise treatment outcomes but also expose lice to sub-therapeutic doses of pediculicides. This exposure may accelerate the development of resistance, leading to an increased burden of pediculosis. There is an evident gap in knowledge regarding the evolution of resistance in Nigerian human lice that must be addressed. Future research should aim to combine toxicological bioassays with epidemiological and socioeconomic assessments to comprehensively evaluate the effectiveness of lice treatments in Nigeria and inform public health strategies to treat pediculosis.