Identification and Characterization of Orientia chuto in Trombiculid Chigger Mites Collected from Wild Rodents in Kenya

Abstract

We present data that concurs with the reported geographical expansion of scrub typhus outside the "Tsutsugamushi Triangle" and addition of <i>Orientia chuto</i> as a second species in the <i>Orientia</i> genus. Wild rodents were caught in Marigat, Baringo County, Kenya, and ectoparasites, including chiggers, were recovered. Rodent and chigger species were identified by taxonomic features. DNA was extracted from the chiggers and used to amplify and/or sequence the 47-kDa high temperature transmembrane protein (TSA47), the 56-kDa type-specific antigen (TSA56), and the 16S rRNA (<i>rrs</i>) <i>Orientia</i> genes. The main rodent hosts identified were <i>Acomys wilsoni</i>, <i>Crocidura</i> sp., and <i>Mastomys natalensis</i>, which accounted for 59.2% of the total collection. Of these, <i>A. wilsoni</i> and <i>M. natalensis</i> harbored most of the chiggers that belonged to the <i>Neotrombicula</i> and <i>Microtrombicula</i> genera. A pool of chiggers from one of <i>M. natalensis</i> was positive for <i>Orientia</i> by TSA47 PCR, but <i>Orientia</i> did not amplify with the TSA56 primers. On sequencing the 850 bp of the TSA47 gene, the closest phylogenetic relative was <i>O. chuto</i>, with 97.65% sequence homology compared to 84.63 to 84.76% for <i>O. tsutsugamushi</i> 16S rRNA deep sequencing also revealed <i>O. chuto</i> as the closest phylogenetic relative, with 99.75% sequence homology. These results and the existing immunological and molecular reports are strongly suggestive of the existence of <i>Orientia</i> species in Kenya.