Epidemiological and molecular insights into human lice (Anoplura: Pediculidae) in France: genetic diversity and DNA barcoding

Human lice are hematophagous ectoparasites of worldwide distribution and public health concern. Despite their medical importance, the genetic diversity of these ectoparasites remains poorly documented, with only one prior study conducted in France. In this study, we investigated the distribution and genetic diversity of human louse populations collected from patients referred to Avicenne Hospital, northern Paris, between 2019 and 2023. A total of 209 specimens, one per patient, were examined: 186 head lice (Pediculus humanus capitis), 11 body lice (Pediculus h. corporis), and 12 pubic lice (Pthirus pubis). Head lice predominated in women (82.3%), whereas body and pubic lice were more frequent in men (81.8% and 83.3%, respectively). Among head lice patients, 75.8% were children under 18 years, while all body lice patients and 83.3% of pubic lice patients were adults. Two infants with pubic lice were diagnosed, presumably infected by their parents, highlighting transmission risk among family members. Four pubic lice cases involved men who have sex with men. Phylogenetic analysis of cytochrome oxidase I (COI) sequences using the maximum likelihood method and comparison to GenBank sequences from multiple regions revealed genetic heterogeneity, with sequences clustering into three monophyletic clades (A, B and C). Clade C is reported for the first time in France. Body louse sequences clustered exclusively within clade A. Together with our previous work, this study represents the first epidemiological investigation of human lice infestation in a general French population, contrasting with earlier reports restricted to schoolchildren. Our findings also improve our understanding of human louse genetic diversity with implications for control strategies.