Hee Il Lee

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi , an obligate intracellular bacterium transmitted by trombiculid mites. Although numerous O. tsutsugamushi strains have been identified in human patients, recovery of viable strains from trombiculid mites remains technically challenging. In this study, we report the successful isolation and stable establishment of three O. tsutsugamushi strains, namely, Boryong, Kawasaki, and Yonchon, directly from field-collected trombiculid mites in the Republic of Korea (ROK). Trombiculid mites collected from wild rodents at four regions (Cheorwon, Cheongju, Geoje, and Hapcheon) in November 2025 were surface-sterilized, homogenized, and screened for O. tsutsugamushi . Positive homogenates were inoculated intraperitoneally into immunodeficient NOD.SCID mice to facilitate in vivo amplification. Spleen homogenates from infected mice collected upon the onset of clinical signs were subsequently propagated in L929 cell cultures. Successful isolation was confirmed by cytopathic effects-like morphological changes, immunofluorescence assay, real-time quantitative PCR, nested PCR, and sequencing of the 56-kDa tsa and 47-kDa htrA genes. Phylogenetic analyses demonstrated that the established isolates clustered within the known Boryong, Kawasaki, and Yonchon lineages. All isolates were stably maintained through serial passages in vitro , exhibited robust intracellular replication, and were free of co-infection with other representative tick- and trombiculid-borne intracellular bacteria. This study provides direct evidence that viable O. tsutsugamushi strains are maintained within natural trombiculid mite populations and can be successfully isolated using a combined in vivo – in vitro approach, representing the first successful isolation of mite-derived strains in the ROK and the first recovery of Boryong, Kawasaki, and Yonchon strains from natural mite hosts. These vector-derived isolates represent valuable biological resources for future studies on the ecology, molecular epidemiology, pathogenesis, and prevention of scrub typhus.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral disease with high case-fatality rates in East Asia. While hard ticks are recognized as the primary vectors of SFTS virus (SFTSV), the detection of SFTSV RNA in chigger mites suggests their involvement in viral maintenance in natural conditions. In this study, wild rodents were captured at 17 sites across the Republic of Korea in 2019, and spleen tissues and mites were collected and tested for SFTSV RNA using RT-PCR. To evaluate transovarial transmission, Leptotrombidium sp. collected from an endemic area were reared under laboratory conditions. Among 56 rodents and 3,402 mites, SFTSV RNA was detected in 3.6% of rodents and 2.3% of mite pools (minimum infection rate of 0.09%). Phylogenetic analysis revealed that all viral sequences clustered within genotype B. SFTSV RNA was detected in both parental mites and their F1 larvae, providing molecular evidence suggestive of transovarial transmission. This study provides the first molecular evidence suggestive of transovarial transmission of SFTSV in chigger mites under laboratory conditions and indicates that chigger mites may contribute to the natural maintenance of the virus. Further animal model-based studies are needed to clarify their vector competence.

Tick-borne parasitic diseases pose important threats to veterinary and public health, particularly in countries with livestock-dependent economies such as Kyrgyzstan. However, molecular epidemiological data on tick-borne pathogens in Kyrgyzstan is limited. This study investigated the prevalence, genetic diversity, and host–tick–pathogen associations in Chuy Province, Kyrgyzstan. A total of 494 ticks belonging to 6 genera and 10 species were collected from various animal hosts in eight survey areas in central-northern Chuy Province and analyzed using polymerase chain reaction, Sanger sequencing, and phylogenetic analysis. Of the 494 ticks, 35 (7.1%) were infected, including 15 (3.0%) with Babesia species and 20 (4.0%) with Theileria species. The highest positive rates were observed in Rhipicephalus annulatus (13.8%) and Haemaphysalis punctata (12.4%). Molecular analysis identified 4 Babesia species (B. caballi, B. major, B. bigemina, B. occultans) and 2 Theileria species (T. orientalis, T. ovis). Ticks collected from horses had the highest infection rates and greatest diversity of pathogens. T. orientalis was the most common pathogen. T. ovis was exclusively found in ticks collected from sheep. Phylogenetic analysis confirmed that the isolates were closely related to strains circulating in neighboring Central Asian and Eurasian countries. The findings provide foundational data for developing region-specific vector control measures.

Osong Public Health and Research Perspectives

In the Republic of Korea (ROK), chloroquine is the first-line treatment for Plasmodium vivax (P. vivax), and primaquine is also prescribed to prevent relapse. For Plasmodium falciparum (P. falciparum), atovaquone-proguanil, pyronaridine-artesunate, and mefloquine are recommended. This study monitored drug resistance genes in blood samples collected from patients with P. vivax (soldiers, relapsed, and imported) and P. falciparum (soldiers and civilians) between 2022 and 2025. In P. vivax, several Pvmdr-1 mutations showed high prevalence, with S515R, G698S, L845F, M908L, T958M, and F1076L observed in nearly all isolates, while T529 and E1233 mutation showed moderate prevalence. S513R, Y541C, A829V, and S1358 mutation were occasionally identified, all of which were imported or soldiers receiving prophylactic chemotherapy. Significant differences in mutation prevalence were identified among groups (p < 0.05). However, no significant temporal trends were observed. In P. falciparum, the Y184F mutation in Pfmdr-1 was highly prevalent, and A675V mutation in PfK13 was detected only in soldiers. Group comparisons revealed significant differences (p < 0.05), whereas temporal trends were not observed. Because drug resistance gene mutations can be closely linked to treatment, surveillance of drug resistance genes is expected to contribute to malaria eradication in the ROK through providing basic information related to treatment.

Until now, 3 Metagonimus spp. (M. yokogawai, M. takahashii, and M. miyatai) causing human metagonimiasis have been reported in Korea. In this study, we investigated the possible presence of Metagonimus spp. other than these 3 species using human fecal samples from an endemic area in Korea. DNA was extracted from Metagonimus egg-positive fecal samples collected from residents of Gurye-gun, Jeollanam-do. A total of 21 representative mitochondrial cytochrome c oxidase subunit I sequences were obtained by PCR and cloning, and sequencing. Phylogenetic analysis revealed 1 cluster corresponding to M. yokogawai (n=10) and 2 additional distinct clusters corresponding to M. kogai (n=8) and M. saitoi (n=3), which were proposed as new species in Japan in 2022. Pairwise cytochrome c oxidase subunit I distances were low for M. yokogawai and M. kogai (mean Kimura 2-parameter: 0.005–0.006), whereas M. saitoi showed higher Korea–Japan values (~0.029), a pattern consistent with geographic structuring. In conclusion, we provide the first molecular evidence for the occurrence of M. kogai and M. saitoi in human fecal samples in Korea. Further confirmation using adult morphology, additional nuclear markers, and ecological surveys are needed to clarify metagonimiasis transmission in the Seomjin-gang (river) basin.

Clonorchis sinensis and Metagonimus spp. are prevalent parasites in Korea, and accurate diagnosis is essential because treatment dosages differ between infections. However, their eggs are morphologically similar under light microscopy, making differentiation difficult and dependent on examiner expertise. To address this limitation, we evaluated an artificial intelligence (AI)-based automated microscope solution for the simultaneous detection and discrimination of both parasites. Microscopic images from 170 stool samples were analyzed using an AI system based on You Only Look Once version 5. The annotated dataset comprised 9455 egg images (6494 C. sinensis and 2961 Metagonimus spp.), randomly divided at the slide/patient level into training (6862), validation (1301), and test (1292) sets. Diagnostic performance was evaluated using mean average precision, confusion matrix analysis, and correlation with conventional microscopy. The model achieved a classification accuracy of up to 97.8%. C. sinensis showed higher recall and F1 scores, whereas Metagonimus spp. showed higher precision and specificity. Species identification showed complete concordance with conventional microscopy, and egg quantification was strongly correlated. These results indicate that the proposed AI system may serve as a supportive diagnostic tool comparable to conventional microscopy.

Orthohantaviruses are zoonotic pathogens that cause severe diseases in humans primarily through inhalation of aerosols from rodent excreta. Recent studies suggest that ectoparasites may be potential vectors for Orthohantaviruses. This study aimed to obtain molecular evidence of Orthohantavirus in trombiculid mites collected from wild rodents. In April 2025, 4963 trombiculid mites were collected from 128 wild rodents captured in 17 regions of the Republic of Korea (ROK). Among them, 1660 mites were grouped into 204 pools by collection sites and tested for the Orthohantavirus RNA using quantitative real-time polymerase chain reaction (PCR) and reverse transcription-nested PCR. OrthoHantavirus RNA was detected in seven trombiculid mite pools, with a minimum infection rate of 0.4/100 mites. Orthohantavirus hantanense was identified in trombiculid mites from Cheongju, Gimcheon, and Yeongdeok, while O. jejuense was identified in trombiculid mites from Boryeong and Jeongeup. Notably, Orthohantaviruses were not detected in the host rodents of the Orthohantavirus-positive trombiculid mites from Cheongju, Jeongeup, and Gimcheon, indicating host-independent infection. This study is the first to report detection of Orthohantaviruses, O. hantanense and O. jejuense, from trombiculid mites in the ROK. The host-independent infection suggests that these mites could serve as independent vectors/reservoirs for Orthohantaviruses, distinct from previously known transmission routes.

Background: Japanese encephalitis virus (JEV) is a major mosquito-borne pathogen, primarily transmitted by Culex tritaeniorhynchus in rural regions. In the Republic of Korea (ROK), genotype V (GV) has become the dominant JEV strain since 2010, raising suspicion about the vector competence of urban mosquitoes like Culex pipiens pallens . Methods: This study evaluated the vector competence of Cx. tritaeniorhynchus and Cx. pipiens pallens for JEV GIII and GV under laboratory conditions. Mosquitoes were orally infected, and the infection rate (IR), dissemination rate (DR), and transmission rate (TR) were assessed at days 7 and 14 post-infection. Results: Culex tritaeniorhynchus showed consistently high IR, DR, and TR for both genotypes, with over 95% of mosquitoes infected and actively transmitting the virus. In contrast, Cx. pipiens pallens exhibited a markedly lower IR, ranging from 23.1 to 39.2%; however, among infected mosquitoes, DR and TR were comparatively high. Viral load and titers were also markedly higher in Cx. tritaeniorhynchus than in Cx. pipiens pallens , particularly in the head-thorax and salivation samples. Conclusions: These findings confirm that Cx. tritaeniorhynchus is a highly competent vector for JEV GIII and GV and suggest that Cx. pipiens pallens may play a notable role in the transmission of Japanese encephalitis virus in urban areas. This study emphasizes the importance of targeted vector surveillance and control strategies for multiple mosquito species, especially given the recent urbanization of JE cases in the ROK. Graphical