High prevalence of knockdown resistance mutations, genetic clade diversity, and detection of Acinetobacter species in head lice (Pediculus humanus capitis) infesting children in a Thai orphanage: A comprehensive survey.

Pediculosis, caused by the head louse (Pediculus humanus capitis), remains a public health challenge among school-aged children. The emergence of resistance to pyrethroid insecticides associated with mutations in the knockdown resistance (kdr) genes may hinder control efforts. Furthermore, head lice have been implicated as potential vectors for bacterial pathogens, raising concerns about their role in disease transmission. Head lice collected from children in an orphanage were analyzed for genetic diversity, kdr-mutation resistance, and the presence of bacterial pathogens. A total of 107 lice samples were screened for the kdr T917I mutation using PCR-RFLP. Clade diversity was assessed through phylogenetic analysis of cytb gene sequences, supported by species delimitation methods. Detection of bacterial pathogens, including Acinetobacter spp. and Bartonella spp., was conducted using PCR targeting the rpoB and gltA genes, respectively. Phylogenetic reconstruction and species delimitation analyses consistently revealed the presence of two distinct genetic clades among the head lice samples: Clade A (69.16%) and Clade C (30.84%). The homozygous resistant (RR) genotype was predominant, observed in 101 individuals (94.39%), with an overall kdr T917I resistance allele frequency of 96%. Molecular screening for bacterial pathogens identified Acinetobacter towneri, A. johnsonii, and Acinetobacter spp. in three samples, while no Bartonella spp. were detected. The study identified significant pyrethroid resistance among head lice in the studied population and a notable presence of Acinetobacter species. This underscores the necessity for ongoing surveillance, especially among vulnerable populations such as children in orphanages.