Tick-borne rickettsiosis results from a member of genus Rickettsia, of the family Rickettsiaceae and the order Rickettsiales . Clinically, SFG rickettsioses are associated with headache, pyrexia, myalgia, localized lymphadenopathy, characteristic eschar, and rash. Following the tick bite, R. raoultii has known to be presents with a clinical syndrome characterized by scalp eschars and neck lymphadenopathy. In 2010, to collectively explain this clinical manifestation, the syndrome was termed as “SENLAT” . To date, 14 distinct tick species from six genera, including Dermacentor (D. nuttallii, D. reticulatus, D. silvarum, and D. marginatus), Ambylomma (A. helvolum), Haemaphysalis (H. concinna, H. japonica, H. erinacei, and H. longicornis), Hyalomma (Hy. asiaticum and Hy. lusitanicum), Ixodes (I. persulcatus and I. ricinus), and Rhipicephalus (Rh. pumilio and Rh. turanicus) have shown the presence of R. raoultii DNA [15, 16]. A report has also shown its presence in Melophagus ovinus, a louse fly or sheep ked . Dermacentor ticks are considered as the main hosts and natural reservoirs of R. raoultii all over Europe and in a few countries of Asia, including China and Mongolia .
In the ROK, the first evidence of the existence of SFG rickettsia in ticks was reported in 2003, followed by the first case of SFG rickettsioses (Japanese spotted fever) in a patient in 2005 [19, 20]. Over the period of 16 years, various species of SFG rickettsial agents from ticks (R. japonica, R. monacensis, and R .rickettsii) and humans (R. japonica and R. monacensis) have been identified in the ROK [19–25] Till date, R. raoultti was not identified in this region, and the present study reports the first detection of R. raoultii belonging to the genus H. longicornis. Previously, only one study from China indicated the presence of R. raoultii in H. longicornis ticks . The strains of R. raoultii, including Marne, 8/9 Karaganda, KhabarovaskT, Shayman, and IM 16, have been documented in Europe, Russia, and China [4, 9]. The present phylogenetic tree showed that the positive samples formed a distinct clade with high (100) bootstrap value with R. raoultii IM 16 strain found in China. The nucleic acids of R. japonica, R. monacensis, and R. rickettsii have been identified in H. longicornis from ROK [19, 23]. According to a recent study, H. longicornis ticks are the most prevalent species in ROK (88.9%) with its geographical distribution nationwide . Despite its identification in multiple tick species, reports on human infections are still lacking. The infection of R. raoultii in patients has been reported in Europe, the Far East of Russia, and a few cases in China . Another study from China  identified R. raoultii DNA in clinical samples, besides the positive serological reports in patients from other countries. Based on these findings, R. raoultii has been considered as a human pathogen .
Present observations indicate the emergence of R. raoultii in ticks from ROK and warrant additional survey for this pathogen in a broader range of ticks. Furthermore, public health providers and physicians should use diagnostic tests of R. raoultii in patients of suspected rickettsioses. A special drive should be undertaken to investigate the presence of this emerging pathogen in human cases