The bacterial microbiome and pathogen reservoir potential of Rhipicephalus sanguineus ticks in South Africa

Background: Tick-borne bacterial pathogens from both domestic and wild animals play a significant role in the (re)emergence of human diseases. Primary tick endosymbionts have considerable influence on tick fitness and pathogen acquisition or transmission, while secondary endosymbionts are more likely to be pathogens. Rhipicephalus sanguineus is one of the most widespread tick species as they predominantly parasitise domestic dogs, though they have also been documented to feed on domestic animals and humans. This makes them ideal vectors of bacterial pathogens that can pose a significant threat to human health. Rhipicephalus sanguineus is host to a species-specific Coxiella endosymbiont. Tick-borne pathogens and endosymbiotic bacteria can be studied through a targeted microbiome approach. Methods: We utilised a 16S rRNA microbiome and amplicon sequence variant (ASV) approach to study the bacterial groups present in the midgut and salivary gland tissues of R. sanguineus ticks collected from dogs in a rural community in Bushbuckridge, Mpumalanga, South Africa, from 2016 to 2019. Results: Post processing, we obtained 43,161 total sequence reads which were clustered into ASVs by sample year. After contaminants were removed there were ASVs belonging to seven genera: Coxiella , Anaplasma , Escherichia/Shigella , Ehrlichia , Borrelia , Rickettsia and Wolbachia . Coxiella endosymbionts dominated the microbiome. In 2017 Anaplasma was introduced to the microbiome and increased at the 2019 sampling. All other genera were present at low levels. Conclusions : Our study highlights the changes in the microbiome of the R. sanguineus ticks over time. We found high numbers of two pathogenic Anaplasma species, A. platys and A. centrale, which cause disease in dogs and cattle, respectively, although A. platys infections in humans have been documented. With the exclusion of Wolbachia , the other detected genera could have pathogenic potential . Given our findings of pathogenic bacterial species, our study highlights the role that R. sanguineus might play as a reservoir of pathogens.