dc.description.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. |
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