Abstract:
The flea-borne rickettsioses murine typhus (Rickettsia typhi) and flea-borne spotted fever (FBSF) (Rickettsia felis)
are febrile diseases distributed among humans worldwide. Murine typhus has been known to be endemic to
Kenya since the 1950s, but FBSF was only recently documented in northeastern (2010) and western (2012) Kenya.
To characterize the potential exposure of humans in Kenya to flea-borne rickettsioses, a total of 330 fleas (134
pools) including 5 species (Xenopsylla cheopis, Ctenocephalides felis, Ctenocephalides canis, Pulex irritans, and
Echidnophaga gallinacea) were collected from domestic and peridomestic animals and from human dwellings
within Asembo, western Kenya. DNA was extracted from the 134 pooled flea samples and 89 (66.4%) pools
tested positively for rickettsial DNA by 2 genus-specific quantitative real-time PCR (qPCR) assays based upon
the citrate synthase (gltA) and 17-kD antigen genes and the Rfelis qPCR assay. Sequences from the 17-kD antigen
gene, the outer membrane protein (omp)B, and 2 R. felis plasmid genes (pRF and pRFd) of 12 selected rickettsiapositive
samples revealed a unique Rickettsia sp. (n = 11) and R. felis (n = 1). Depiction of the new rickettsia by
multilocus sequence typing (MLST) targeting the 16S rRNA (rrs), 17-kD antigen gene, gltA, ompA, ompB, and
surface cell antigen 4 (sca4), shows that it is most closely related to R. felis but genetically dissimilar enough to be
considered a separate species provisionally named Candidatus Rickettsia asemboensis. Subsequently, 81 of the
134 (60.4%) flea pools tested positively for Candidatus Rickettsia asemboensis by a newly developed agentspecific
qPCR assay, Rasemb. R. felis was identified in 9 of the 134 (6.7%) flea pools, and R. typhi the causative
agent of murine typhus was not detected in any of 78 rickettsia-positive pools assessed using a species-specific
qPCR assay, Rtyph. Two pools were found to contain both R. felis and Candidatus Rickettsia asemboensis DNA
and 1 pool contained an agent, which is potentially new.
