Candidatus Rickettsia hoogstraalii in Ethiopian Argas persicus ticks

Ethiopian soft ticks Argas persicus, hard ticks including both Amblyomma variegatum and Rhipicephalus (Boophilus) spp., and fleas were collected from livestock, traditional human dwellings, and cracks and crevices of trees. They were assessed in pools for the presence of Rickettsia using PCR-based methods. The extracted tick DNA was subjected to molecular screening for Rickettsia, which revealed 50.5% of the pooled samples to be positive for Rickettsia spp. These were then subjected to multi-gene analysis using both outer surface proteins and housekeeping genes with proven discriminatory potential. Sequencing of the citrate synthase and outer membrane genes clearly led to the identification of three distinct rickettsial species, Candidatus Rickettsia hoogstraalii in Argas persicus ticks; R. africae in hard tick pools, and R. felis in fleas. Furthermore, we demonstrated the presence of the plasmid-borne small heat-shock protein gene hsp2 in DNA from A. persicus ticks suggesting that Candidatus R. hoogstraalii carried by these ticks possess a plasmid. Unlike chromosomal gene sequences, the hsp2 gene failed to cluster with Candidatus R. hoogstraalii, instead falling into an isolated separate clade, suggesting a different origin for the plasmid.