Genetic diversity and occurrence of permethrin resistance-associated mutations in a population of head lice (Pediculus humanus capitis) from Seville, Spain.

Human head lice (Pediculus humanus capitis De Geer, 1767) remain a public health concern, largely due to their widespread resistance to commonly used pediculicides. This study assessed genetic diversity and permethrin resistance in head lice collected from individuals in Seville, Spain. A total of 402 lice were sampled, of which 27 specimens were selected for detailed morphological, molecular, and phylogenetic analyses. Molecular characterization based on mitochondrial markers (cox1, cob and 12S) revealed a specific pattern of genetic diversity, identifying two distinct clades (A and B), with low sequence similarity between them, and clade B predominating in the sampled population. Geometric morphometric analyses revealed significant global size differences between clades A and B, with clade B lice being the largest specimens. All analyzed lice carried three mutations (M815I, T917I and L920F) in the voltage-sensitive sodium channel (VSSC) gene, indicating fixation of alleles associated with permethrin resistance. These findings provide preliminary evidence of permethrin resistance-associated mutations in head lice from Seville and underscore the need for larger studies to determine their frequency and epidemiological significance. Moreover, this study represents the first molecular characterization of head lice in this region and supports the combined use of morphometric and molecular approaches to better understand lice diversity and resistance patterns.