Bartonella species are vector-borne pathogens that infect a wide range of hosts, including humans. Although several Bartonella species have been identified in rodents and arthropods in Korea, information on Bartonella detection in ticks removed from human patients remains limited. This study investigated the presence of Bartonella species DNA in human-biting ticks collected in Korea and screened for other tick-associated bacteria, including Coxiella endosymbiont. From January to December 2018, 35 ticks were removed from 29 tick-bitten patients in Jeollanam-do and Gwangju, Korea. Ticks were identified morphologically and molecularly by 16S rRNA gene PCR. The presence of Bartonella species was assessed using nested PCR targeting the 16S-23S internal transcribed spacer (ITS) region. The ticks were identified as Haemaphysalis longicornis (17/35, 48.6%), Amblyomma testudinarium (14/35, 40.0%), and Ixodes nipponensis (4/35, 11.4%). Two H. longicornis ticks tested positive for Bartonella species. Sequencing revealed 99.5% identity with B. bacilliformis isolate GJRITS124 in one tick and 98.9% identity with B. taylorii isolate 190731_HC2 in the other, both previously identified in Apodemus agrarius rodents in Korea. One B. bacilliformis-positive tick was also positive for Coxiella spp., and sequence analysis indicated a Coxiella endosymbiont showing 100.0% identity with the Coxiella-like endosymbiont strain 580. Phylogenetic analysis supported these findings; however, bacterial cultures from PCR-positive tick lysates were negative. This study provides baseline evidence of B. bacilliformis and B. taylorii, as well as Coxiella endosymbiont DNA in human-biting H. longicornis ticks in Korea and highlights the need for continued surveillance.

Accurate identification of tick species is essential for understanding their role in pathogen transmission and guiding vector control strategies. Although morphological classification is widely used, it can be limited by specimen damage or immature developmental stages. In this study, we comparatively evaluated mitochondrial 16S and 12S ribosomal DNA (rDNA) markers for species-level identification and morphological verification of hard ticks and rodent-associated ectoparasites collected from vegetation, wild rodents, and patients in Gwangju, Republic of Korea. A total of 74 morphologically identified adult ticks—Haemaphysalis longicornis, Haemaphysalis flava, and Ixodes nipponensis—along with 3 damaged ticks removed from patients, were analyzed. PCR and sequencing success varied among species and markers. The 16S rDNA marker showed a higher amplification rate but lower sequencing success, whereas 12S rDNA showed more consistent performance. I. nipponensis showed the most balanced performance (89.5% for 16S and 78.9% for 12S), H. flava showed moderate variation, and H. longicornis demonstrated strong marker dependence, with low 16S but complete 12S success. Importantly, 16S rDNA identified 3 severely damaged ticks from patients—2 I. nipponensis and 1 Amblyomma testudinarium—demonstrating its diagnostic value when morphology was uninformative. Phylogenetic analyses of both markers yielded well-supported clades consistent with morphological identification. Additionally, 12S rDNA identified 3 flea specimens (Ctenophthalmus sp. and Neopsylla specialis) obtained during tick collection from wild rodents, indicating exploratory applicability to other rodent-associated ectoparasites. These findings support mitochondrial 16S and 12S rDNA markers as reliable tools for tick identification, especially when morphological assessment is limited by damage or developmental stage.

Coxiella burnetii, the causative agent of Q fever, is a zoonotic pathogen for which epidemiological data are limited in Mongolia. This study investigated the presence of C. burnetii in ticks collected across Mongolia from forest, pasture, and livestock-associated environments. A total of 7,511 ticks were collected from 42 Soums across 12 provinces and 2 districts of Ulaanbaatar between May and June 2018. Molecular detection of Coxiella-related organisms was performed using 46 DNA samples, comprising 28 individual-tick samples and 18 pooled-tick samples representing 489 ticks, by nested PCR targeting IS1111 and the 16S rRNA gene. Twenty DNA samples (2 individual ticks and 18 pools) were PCR-positive. Sequencing and phylogenetic analysis revealed that 9 Hyalomma asiaticum tick pools contained 16S rRNA sequences of C. burnetii, whereas 11 Dermacentor nuttalli samples (2 individual ticks and 9 pools) contained 16S rRNA sequences of a Coxiellaceae bacterium. Two individual D. nuttalli ticks yielded IS1111 sequences closely related to C. burnetii, whereas the corresponding 16S rRNA sequences clustered with a Coxiellaceae bacterium, highlighting discordance between the 2 molecular targets. The C. burnetii sequences detected in H. asiaticum were closely related to clade A strains reported from the United States, Japan, Greenland, and Korea, whereas sequences detected in D. nuttalli clustered with Coxiella endosymbiont sequences. This study provides molecular evidence for the presence of C. burnetii in H. asiaticum tick pools in Mongolia and demonstrates that Mongolian ticks harbor genetically diverse Coxiella-related bacteria, highlighting the need for further investigation of their epidemiological significance.