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 ofOrientia chutoas a second species in theOrientiagenus. 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 (rrs)Orientiagenes. The main rodent hosts identified wereAcomys wilsoni,Crocidurasp., andMastomys natalensis, which accounted for 59.2% of the total collection. Of these,A. wilsoniandM. natalensisharbored most of the chiggers that belonged to theNeotrombiculaandMicrotrombiculagenera. A pool of chiggers from one ofM. natalensiswas positive forOrientiaby TSA47 PCR, butOrientiadid not amplify with the TSA56 primers. On sequencing the 850 bp of the TSA47 gene, the closest phylogenetic relative wasO. chuto, with 97.65% sequence homology compared to 84.63 to 84.76% forO. tsutsugamushi. 16S rRNA deep sequencing also revealedO. chutoas the closest phylogenetic relative, with 99.75% sequence homology. These results and the existing immunological and molecular reports are strongly suggestive of the existence ofOrientiaspecies in Kenya.

Identification of trombiculid mites (Acari: Trombiculidae) on rodents from Chiloé Island and molecular evidence of infection with Orientia species

“…Although scrub typhus in Asia-Pacific is transmitted by chiggers, in Chile and other possible newly identified endemic regions, the vector is unknown. Interestingly, a study from 2018 found the first molecular evidence for Candidatus Orientia chuto infection of chiggers collected from a rodent in Kenya [31], another region outside the tsutsugamushi triangle, where scrub typhus might occur as suggested by two recent retrospective surveys, detecting antibodies to Orientia spp. in 3% to 5% of febrile patients [5,31].…”

First identification of trombiculid mites (Acari: Trombiculidae) on rodents captured on Chiloé Island, an endemic region of scrub typhus in southern Chile

“…Although scrub typhus in Asia-Pacific is transmitted by chigger mites, in Chile and other possible endemic regions, the vector is unknown. Interestingly, a study from 2018 found first molecular evidence for Orientia chuto infection in chiggers collected from a rodent in Kenya [29], another region outside the tsutsugamushi triangle, where scrub typhus might occur as suggested by two recent retrospective surveys, detecting antibodies to Orientia spp. in 3% to 5% of febrile patients [5,29].…”

“…Interestingly, a study from 2018 found first molecular evidence for Orientia chuto infection in chiggers collected from a rodent in Kenya [29], another region outside the tsutsugamushi triangle, where scrub typhus might occur as suggested by two recent retrospective surveys, detecting antibodies to Orientia spp. in 3% to 5% of febrile patients [5,29]. In the endemic regions in Asia-Pacific, the disease is transmitted by different Leptotrombidium species; however, mites of this genus are not endemic in Chile or any other region of the Neotropics [30].…”

Rickettsioses in Sri Lanka – A mini review

“…7 Recently, a novel Orientia species, Orientia chuto, has been described from a patient in Dubai and from mites in Kenya, indicating the possibility of becoming an emerging pathogen. 8,9 Other Rickettsioses In addition to the above three groups of diseases, human ehrlichiosis and anaplasmosis, and Q fever caused by Coxiella burnetii are also frequently included under the term rickettsioses.…”