# Detection and Genetic Diversity of Heritable Bacterial Symbionts in Human Lice Based on 16S‐rRNA Gene

## TL;DR

This study explores the genetic diversity of bacteria living inside human lice, finding that these bacteria are common and vary across lice types.

## Contribution

The study provides new insights into the genetic diversity and distribution of endosymbiotic bacteria in human lice using 16S-rRNA gene analysis.

## Key findings

- Candidatus Riesia and Wolbachia bacteria were found in high proportions across head, body, and pubic lice.
- Phylogenetic analysis revealed distinct clades among the symbionts, with Candidatus Riesia pthiripubis exclusive to pubic lice.
- No strong correlation was found between symbiont presence and lice type or geographic origin.

## Abstract

Human lice are obligate bloodsucking ectoparasites harbouring endosymbiotic bacteria essential for their survival. Despite the medical significance of human lice, their endosymbionts remain understudied, and knowledge about their species identity, prevalence and genetic diversity is largely limited. Head, body and pubic louse specimens' collection from infested patients of various origins between 2019 and 2023 enabled molecular screening for distribution and genetic diversity of bacterial endosymbionts through conventional PCR targeting two fragments of 16S‐rRNA. A total of 209 louse specimens isolated from infested patients, including 186 head lice, 11 body lice and 12 pubic lice were examined with 77.5%, 41.7% and 94.3% of the specimens found to be infested with Candidatus Riesia pediculicola, Candidatus Riesia pthiripubis and Wolbachia respectively. Inferred phylogenetic analysis of Candidatus Riesia and Wolbachia sequences revealed heterogeneity clustering into four and three clades respectively. No specific correlation was observed between these endosymbionts and lice ecological forms or geographical origin demonstrating that head, body and pubic lice share the same Candidatus Riesia and Wolbachia strains with independent adaptation and co‐evolution, except Candidatus Riesia pthiripubis which was identified exclusively in pubic lice. These phylogenetic results were aligned by network analysis. These findings could be helpful in evolutionary and biological control investigations.

Candidatus Riesia pediculicola and Wolbachia were found in 79.6% and 95.2% of head lice, and 81.8% and 100% of body lice. Candidatus Riesia pthiripubis and Wolbachia appeared in 41.7% and 75% of pubic lice. Maximum‐likelihood 16S‐rRNA phylogeny revealed substantial heterogeneity within symbiont populations.