Abstract:
Tick-borne spotted fever group (SFG) rickettsioses are emerging human diseases caused by obligate intracellular
Gram-negative bacteria of the genus Rickettsia. Despite being important causes of systemic febrile
illnesses in travelers returning from sub-Saharan Africa, little is known about the reservoir hosts of these
pathogens. We conducted surveys for rickettsiae in domestic animals and ticks in a rural setting in western
Kenya. Of the 100 serum specimens tested from each species of domestic ruminant 43% of goats, 23% of sheep,
and 1% of cattle had immunoglobulin G (IgG) antibodies to the SFG rickettsiae. None of these sera were
positive for IgG against typhus group rickettsiae. We detected Rickettsia africae–genotype DNA in 92.6% of
adult Amblyomma variegatum ticks collected from domestic ruminants, but found no evidence of the pathogen
in blood specimens from cattle, goats, or sheep. Sequencing of a subset of 21 rickettsia-positive ticks revealed
R. africae variants in 95.2% (20/21) of ticks tested. Our findings show a high prevalence of R. africae variants
in A. variegatum ticks in western Kenya, which may represent a low disease risk for humans. This may provide
a possible explanation for the lack of African tick-bite fever cases among febrile patients in Kenya.
