Detection of a Knockdown Resistance Mutation Associated with Permethrin Resistance in the Body Louse Pediculus humanus corporis by Use of Melting Curve Analysis Genotyping

Abstract

Louse-borne diseases are prevalent in the homeless, and body louse eradication has thus far been unsuccessful in this population. We aim to develop a rapid and robust genotyping method usable in large field-based clinical studies to monitor permethrin resistance in the human body louse Pediculus humanus corporis. We assessed a melting curve analysis genotyping method based on real-time PCR using hybridization probes to detect the M815I-T917I-L920F knockdown resistance (kdr) mutation in the paraorthologous voltage-sensitive sodium channel (VSSC) ␣ subunit gene, which is associated with permethrin resistance. The 908-bp DNA fragment of the VSSC gene, encoding the ␣ subunit of the sodium channel and encompassing the three mutation sites, was PCR sequenced from 65 lice collected from a homeless population. We noted a high prevalence of the 3 indicated mutations in the body lice collected from homeless people (100% for the M815I and L920F mutations and 56.73% for the T917I mutation). These results were confirmed by melting curve analysis genotyping, which had a calculated sensitivity of 100% for the M815I and T917I mutations and of 98% for the L920F mutation. The specificity was 100% for M815I and L920F and 96% for T917I. Melting curve analysis genotyping is a fast, sensitive, and specific tool that is fully compatible with the analysis of a large number of samples in epidemiological surveys, allowing the simultaneous genotyping of 96 samples in just over an hour (75 min). Thus, it is perfectly suited for the epidemiological monitoring of permethrin resistance in human body lice in large-scale clinical studies.T he human body louse Pediculus humanus corporis (P. h. corporis) is a hematophagous ectoparasite that lives and multiplies in clothing. Body lice are vectors of 3 major infectious diseases: epidemic typhus caused by Rickettsia prowazekii, relapsing fever caused by Borrelia recurrentis, and trench fever caused by Bartonella quintana (24). The poor living conditions and crowded situations in homeless, war refugee, or natural disaster victim populations provide ideal conditions for the spread of lice (23). Body louse infestation has been observed in 22% of the sheltered homeless population in Marseille, France, causing trench fever, epidemic typhus, and relapsing fever (4), and coinfestation with head lice is often noted. Consequently, all measures that can be used to decrease the burden of these ectoparasites in homeless people are warranted to avoid the spread and/or outbreak of these diseases. Clothing change as well as the use of ivermectin to eradicate the body lice in a cohort of homeless individuals in Marseille was unsuccessful (10), suggesting that the complete eradication of this ectoparasite is a true challenge (1, 5). It was therefore essential for us to investigate other strategies to reach this goal.During the 1980s, a study conducted by the U.S. Army demonstrated that the use of uniforms impregnated with 0.125 mg/ cm 2 permethrin effectively eradicated body lice (28). The resistance to permethrin, ...

Effect of Permethrin–Impregnated Underwear on Body Lice in Sheltered Homeless Persons

“…Significant reductions from the baseline in the mean number of body lice were observed on day 14 and day 45 in the permethrin and placebo groups (see eTable 2 in the Supplement). However, no significant difference was found between the 2 groups on day 14…”

“…The permethrin resistance of body lice was determined in a representative random sample of body lice collected from all body lice-infested homeless persons and stratified by the level of infestation of the homeless persons (see eTable 1 in the Supplement). A melting curve analysis genotyping method, 14 based on a previously reported real-time polymerase chain reaction using hybridization probes, was used to detect the 3 mutations (M815I, T917I, and L920F), identified in the voltage-sensitive sodium channel α-subunit gene, responsible for knockdown resistance (kdr). According to the literature, these 3 mutations define the RRR haplotype, which confers permethrin resistance in head lice.…”

Nuclear Genetic Diversity in Human Lice (Pediculus humanus) Reveals Continental Differences and High Inbreeding among Worldwide Populations

“…These demographic events are expected to have genome-wide effects by reducing genetic polymorphisms in the louse genome. Whereas insecticide resistance is well known for head lice, it is less common in clothing lice and only recently has a study performed kdr -allele typing for clothing lice from France [16]. Further studies including sympatric clothing and head louse populations are needed to discern the role of these factors in shaping the genetic structure and diversity of human lice.…”

“…Pyrethroid resistance in human lice is due to three knockdown ( kdr )-type point mutations (M815I, T917I, and L920) in the voltage-sensitive sodium channel alpha-subunit gene [12], [13]. The kdr -type resistance has been reported in many countries among head louse populations [14], [15], and recently in clothing lice from France [16]. In order to better understand how these resistance alleles are spread, we must also have a firm understanding of neutral genetic variation and patterns of gene flow among populations of lice.…”

Management and Treatment of Human Lice

“…It is one of the most frequently used treatments against human ectoparasites (head lice and scabies) among lindane, malathion, and carbaryl [ 34 , 115 ]. However, resistance to permethrin has been reported in many studies throughout the world [ 116 – 120 ]. In clinical trial, permethrin compared to soya oil-based shampoo, coconut, and anise in spray has been less effective [ 39 , 40 ].…”