Hammoud A. auteur aut IRD Louni M. auteur aut IRD Missé Dorothée auteur aut IRD Cortaredona Sébastien auteur aut IRD Fenollar F. auteur aut IRD Mediannikov Oleg auteur aut IRD text journalArticle eng text/pdf reformatted digital access Background: The human louse (Pediculus humanus) is a haematophagous ectoparasite that is intimately related to its host. It has been of great public health concern throughout human history. This louse has been classified into six divergent mitochondrial clades (A, D, B, F, C and E). As with all haematophagous lice, P. humanus directly depends on the presence of a bacterial symbiont, known as "Candidatus Riesia pediculicola", to complement their unbalanced diet. In this study, we evaluated the codivergence of human lice around the world and their endosymbiotic bacteria. Using molecular approaches, we targeted lice mitochondrial genes from the six diverged clades and Candidatus Riesia pediculicola housekeeping genes. Methods: The mitochondrial cytochrome b gene (cytb) of lice was selected for molecular analysis, with the aim to identify louse Glade. In parallel, we developed four PCR primer pairs targeting three housekeeping genes of Candidatus Riesia pediculicola: ftsZ, groEL and two regions of the rpoB gene (rpoB-1 and rpoB-2). Results: The endosymbiont phylogeny perfectly mirrored the host insect phylogeny using the ftsZ and rpoB-2 genes, in addition to showing a significant co-phylogenetic congruence, suggesting a strict vertical transmission and a host- symbiont co-speciation following the evolutionary course of the human louse. Conclusion: Our results unequivocally indicate that louse endosymbionts have experienced a similar co-evolutionary history and that the human louse Glade can be determined by their endosymbiotic bacteria. specialized Human lice Candidatus Riesia pediculicola Co-evolution Mitochondrial genes Housekeeping genes Phylogenetic analysis 052 020 15 1 73 [9 ] 2022 1756-3305 https://www.documentation.ird.fr/hor/fdi:010084513 10.1186/s13071-022-05203-z 1756-3305 [F B010084513] https://www.documentation.ird.fr/hor/fdi:010084513 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2022-04/010084513.pdf IRD - Base Horizon / Pleins textes 2022-04-06 2025-02-24 fdi:010084513 fre