High prevalence of pediculosis, associated factors, and exploratory detection of the knockdown resistance mutations in head lice from school settings in Chonburi Province, eastern Thailand

Head louse infestation ( Pediculosis humanus capitis ) remains a common public health problem among school-aged children. While reduced efficacy of pediculicides has been increasingly reported, information linking prevalence, treatment-related factors, and molecular detection of resistance-associated kdr mutations in eastern Thailand remain limited. This study investigated the prevalence of pediculosis and exploratory epidemiological associations among schoolchildren in Chonburi Province, eastern Thailand, together with exploratory molecular characterization of resistance-associated kdr mutations and genotype patterns in head lice collected from the same school settings. Pediculosis screening was conducted among 960 schoolchildren attending five public schools in urban and rural areas of Chonburi Province between May and July 2024. Lice collected from infested children were morphologically identified and analyzed for mitochondrial cox 1 clades. Resistance-associated kdr mutations (T917I and L920F) and genotypic forms were explored in a stratified subsample of lice using polymerase chain reaction and sequencing. Factors associated with pediculosis were analyzed using logistic regression. The overall prevalence of pediculosis was 20.42% (95% CI 17.91–23.11) and was higher in rural schools than in urban schools. Pediculosis showed epidemiological associations with sex, school level, hair length, and reported history of pediculicide use. All lice samples were identified as Pediculus humanus capitis , belonging to mitochondrial clades A or C. Resistance-associated kdr mutations were detected, and homozygous resistant genotypes were identified in lice collected from four sampled schools. Resistance-associated genotypes were detected among children both with and without reported histories of permethrin treatment. Pediculosis was common among schoolchildren in Chonburi Province, eastern Thailand, and was associated with sex, school level, hair length, and reported history of pediculicide use. This integrated study also provides exploratory molecular evidence indicating the presence of resistance-associated kdr mutations, including homozygous resistant genotypes detected across multiple sampled schools within a setting where previous studies have reported incomplete treatment outcomes following permethrin use. Although molecular findings alone cannot confirm clinical resistance, these findings highlight potential resistance-related concerns and support continued molecular surveillance, phenotypic validation studies, and future evaluation of coordinated management approaches in endemic settings.