Detection of Spotted Fever Group Rickettsioses, Coxiella Burnetii and Theileria Orientalis in human blood and tick samples from pastoral communities in Kenya

Abstract

The tick-borne human diseases caused by Rickettsia spp., Coxiella burnetii and Babesia spp. are rarely reported in Kenya and yet these infections are likely contributors to undiagnosed febrile disease especially among pastoral communities. The objective of the present study was to assess the prevalence of Spotted fever group Rickettsia spp., Coxiella burnetii and Babesia spp. in human blood and tick samples from pastoral communities in Kenya and to determine the tick species involved in their maintenance and transmission. Archived human blood samples (278) and ticks (380 pools) collected from several geographically dispersed pastoral communities in Kenya were tested for Rickettsia spp., Coxiella burnetii and Babesia spp. by PCR. For Rickettsia spp., three primers sets were used which target the citrate synthase gene (gltA) primer and the outer membrane protein gene (ompA and ompB). A primer targeting the transposon-like IS1111 region was used to detect Coxiella burnetii. The Babesia spp. primer targeted the conserved β-tubulin gene that is able to detect piroplasms of Babesia and Theileria species. A subset of all PCR positive samples were sequenced and data compared with reference sequences in the GenBank. Rickettsia spp. were detected in 14% (39/278) of human blood samples tested using the gltA primer set. On the other hand, 25% of all tick pools screened were positive for Rickettsia spp. using the gltA primer set. Subsequently, all gltA positive tick samples were tested using OmpA and OmpB primers, 21.1 % were positive for the ompA gene and 28.4 % were positive for the ompB gene. Ticks collected from camels (60%) were significantly more infected with Rickettsia spp. C. burnetii was xv detected in 5.53% of the tick tested. On the contrary, all the human blood samples were negative for Coxiella burnetii DNA. All the human blood and tick samples tested were negative for Babesia spp. DNA. However, Theileria orientalis, a related piroplasm was detected in a tick pool collected from a goat in Marigat. In conclusion, the findings in this study suggest that Rickettsia spp. may contribute to a significant proportion of febrile illness in Kenya with multiple rickettsial species circulating among tick and human populations in pastoral communities. In addition, R. aeschlimannii and R. raoultii, which have never been reported before in human samples in Kenya, was detected in the blood samples we tested. Moreover, positive ticks from camels, implicated camels in the maintenance of SFG rickettsia in Kenya. Finally, the study underscores the need for increased diagnostic capacity for rickettsiosis and the monitoring of Coxiella and Theileria in livestock population. It also highlights the need for livestock to be sprayed with acaricides to control ticks and prevent transmission.