Coxiella burnetii is an environmentally stable intracellular bacterium responsible for severe global outbreaks of the zoonotic disease, Q fever. Q fever is transmitted by the inhalation of aerosols contaminated with the birth products and excretions of infected animals, mainly of sheep and goats. A 28-year-old cattle raiser presented with headache and fever without a significant medical history, although his cattle herd had previously been diagnosed with brucellosis. He spent time outdoors but reported no tick bites or eschar. Initial evaluation revealed mild thrombocytopenia and elevated aspartate aminotransferase, alanine aminotransferase, and C-reactive protein levels. On day 2 after disease onset, his blood tested positive for the IS1111 gene of C. burnetii by nested PCR. After amplifying C. burnetii in severe combined immunodeficient mice, the pathogen was isolated using a cell culture system. The isolated CH12 strain was confirmed via PCR, nucleotide sequence analysis, and whole-genome sequencing. This study reports a case of acute Q fever in Korea, in which C. burnetii was isolated and characterized using whole-genome sequencing.

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.

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.