Molecular detection of <i>Bartonella</i> species and <i>Coxiella</i> endosymbiont in human-biting <i>Haemaphysalis longicornis</i> ticks in Korea

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.