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

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.