Severe Fever with Thrombocytopenia Syndrome Virus in Ticks in the Republic of Korea.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a zoonotic, tick-borne RNA virus of the genus Bandavirus (Family Phenuiviridae), mainly reported in China, Japan, and the Republic of Korea (Korea). For the purpose of this study, a total of 3,898 adult and nymphal ticks of species Haemaphysalis longicornis (94.2%), Haemaphysalis flava (5.0%), Ixodes nipponensis (0.8%), and 1 specimen of Ixodes ovatus, were collected from the Deogyusan National Park, Korea, between April 2016 and June 2018. A single-step reverse transcriptase-nested PCR was performed, targeting the S segment of the SFTSV RNA. Total infection rate (IR) of SFTSV in individual ticks was found to be 6.0%. Based on developmental stages, IR was 5.3% in adults and 6.0% in nymphs. The S segment sequences obtained from PCR were divided into 17 haplotypes. All haplotypes were phylogenetically clustered into clades B-2 and B-3, with 92.7% sequences in B-2 and 7.3% in B-3. These observations indicate that the Korean SFTSV strains were closer to the Japanese than the Chinese strains. Further epidemiological studies are necessary to better understand the characteristics of the Korean SFTSV and its transmission cycle in the ecosystem.

Molecular surveillance of zoonotic pathogens from wild rodents in the Republic of Korea.

BACKGROUND: Rodents are recognized as major reservoirs of numerous zoonotic pathogens and are involved in the transmission and maintenance of infectious diseases. Furthermore, despite their importance, diseases transmitted by rodents have been neglected. To date, there have been limited epidemiological studies on rodents, and information regarding their involvement in infectious diseases in the Republic of Korea (ROK) is still scarce. METHODOLOGY/PRINCIPAL FINDINGS: We investigated rodent-borne pathogens using nested PCR/RT-PCR from 156 rodents including 151 Apodemus agrarius and 5 Rattus norvegicus from 27 regions in eight provinces across the ROK between March 2019 and November 2020. Spleen, kidney, and blood samples were used to detect Anaplasma phagocytophilum, Bartonella spp., Borrelia burgdorferi sensu lato group, Coxiella burnetii, Leptospira interrogans, and severe fever with thrombocytopenia syndrome virus (SFTSV). Of the 156 rodents, 73 (46.8%) were infected with Bartonella spp., 25 (16.0%) with C. burnetii, 24 (15.4%) with L. interrogans, 21 (13.5%) with A. phagocytophilum, 9 (5.8%) with SFTSV, and 5 (3.2%) with Borrelia afzelii. Co-infections with two and three pathogens were detected in 33 (21.1%) and 11 rodents (7.1%), respectively. A. phagocytophilum was detected in all regions, showing a widespread occurrence in the ROK. The infection rates of Bartonella spp. were 83.3% for B. grahamii and 16.7% for B. taylorii. CONCLUSIONS/SIGNIFICANCE: To the best of our knowledge, this is the first report of C. burnetii and SFTSV infections in rodents in the ROK. This study also provides the first description of various rodent-borne pathogens through an extensive epidemiological survey in the ROK. These results suggest that rodents harbor various pathogens that pose a potential threat to public health in the ROK. Our findings provide useful information on the occurrence and distribution of zoonotic pathogens disseminated among rodents and emphasize the urgent need for rapid diagnosis, prevention, and control strategies for these zoonotic diseases.

Prevalence, Isolation, and Molecular Characterizationof Severe Fever with Thrombocytopenia Syndrome Virus in Cattle from the Republic of Korea.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by Bandavirus dabieense. Initially identified in China, this disease has spread throughout Asian countries via tick bites and animal-to-human transmission. However, reports of the prevalence of SFTS virus (SFTSV) in cattle in Korea are lacking. This study aimed to investigate SFTSV infections in grazing cattle in the Republic of Korea (ROK). Materials and Methods: In total, 845 grazing cattle serum samples were collected over 2 years (2019 and 2020) in the ROK, and viral RNA was extracted using a kit. One-step RT-nested PCR was performed to amplify the S-segment of SFTSV. Positive serum samples were used to isolate SFTSV in Vero E6 cells, and the full sequences were analyzed. A phylogenetic tree was constructed using the maximum-likelihood method with MEGA X. In addition, immunoglobulin G antibodies against SFTSV were investigated using an enzyme-linked immunosorbent assay. Results: Here, 4.0% of serum samples (34/845) were positive for SFTSV S-segments, and one virus isolate was cultured in Vero E6 cells. Phylogenetic analysis based on the partial S-segment classified 4 SFTSV isolates as the B-2 genotype, 9 as the B-3 genotype, 18 as an unclassified B genotype, and 3 as the D genotype. One cultured virus was classified as the B-2 genotype based on SFTSV L-, M-, and S-segments. Antibody detection results showed that 21.1% of serum samples (161/763) were positive for SFTSV. Conclusion: To the best of our knowledge, this is the first study performed to identify the prevalence of SFTSV in grazing cattle in the ROK. Our findings indicate the necessity for more intensive and continuous SFTSV monitoring, not only in cattle but also in other animals, to comprehend the genetic diversity of the virus and its potential eco-epidemiological impact on human health.

Vaccine Development for Severe Fever with Thrombocytopenia Syndrome Virus in Dogs.

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening viral zoonosis. The causative agent of this disease is the Dabie bandavirus, which is usually known as the SFTS virus (SFTSV). Although the role of vertebrates in SFTSV transmission to humans remains uncertain, some reports have suggested that dogs could potentially transmit SFTSV to humans. Consequently, preventive measures against SFTSV in dogs are urgently needed. In the present study, dogs were immunized three times at two-week intervals with formaldehyde-inactivated SFTSV with two types of adjuvants. SFTSV (KCD46) was injected into all dogs two weeks after the final immunization. Control dogs showed viremia from 2 to 4 days post infection (dpi), and displayed white pulp atrophy in the spleen, along with a high level of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assay (TUNEL) positive area. However, the inactivated SFTSV vaccine groups exhibited rare pathological changes and significantly reduced TUNEL positive areas in the spleen. Furthermore, SFTSV viral loads were not detected at any of the tested dpi. Our results indicate that both adjuvants can be safely used in combination with an inactivated SFTSV formulation to induce strong neutralizing antibodies. Inactivated SFTSV vaccines effectively prevent pathogenicity and viremia in dogs infected with SFTSV. In conclusion, our study highlighted the potential of inactivated SFTSV vaccination for SFTSV control in dogs.

First detection of Bandavirus dabieense in ticks collected from migratory birds in the Republic of Korea.

The causative agent of severe fever with thrombocytopenia syndrome (SFTS) is Bandavirus dabieense, an emerging tick-borne zoonotic pathogen. Migratory birds have often been suggested as potential carriers of ticks that can transmit Bandavirus dabieense; however, their role remains unclear. The Republic of Korea (ROK) holds an important position as a stopover on the East Asian-Australasian Flyway. The present study aimed to investigate the potential involvement of migratory birds in the transmission of the SFTS virus (SFTSV) in the ROK. A total of 4,497 ticks were collected across various regions, including Heuksando and Daecheongdo, in the ROK, from bird migration seasons in 2022 and 2023. Genetic analysis of the SFTSV was performed for 96 ticks collected from 20 different species of migratory birds. Polymerase chain reaction (PCR) fragments of SFTSV were detected in one Haemaphysalis concinna nymph collected from a Black-faced Bunting (Emberiza spodocephala) and one Ixodes turdus nymph collected from an Olive-backed Pipit (Anthus hodgsoni) on Daecheongdo and Heuksando, respectively, during their northward migration in two spring seasons. This finding suggests that migratory birds can be considered as possible carriers and long-distance dispersers of ticks and associated tick-borne diseases. This study highlights the importance of clarifying the role and impact of migratory birds in the rapid expansion of tick-borne diseases, facilitating enhanced preparedness and the development of mitigation measures against emerging SFTS across and beyond East Asia.

Ixodid ticks from wild and domestic animals in East and Central Asian flyways.

Tick-borne diseases have a significant impact on human and animal populations, posing an increasing threat to public health, particularly in the context of climate change. Along with the various natural hosts of ticks, birds play a notable role in transmitting ticks and tick-borne pathogens, indicating the importance of monitoring flyways and establishing a cooperative network for comprehensive surveillance and to collect diverse tick samples across various regions. This study aimed to develop an international network for surveillance of disease, collection of sufficient tick samples, and overall identification of the geographical distribution of host and ticks in Asian regions, especially in 11 countries on East Asian and Central Asian flyways. Ticks were collected from wild animals, domestic animals, and vegetation to identify the differences between Ixodid ticks and understand tick distribution. We collected a total 6,624 of ticks from 11 collaborating Asian countries, the Republic of Korea (ROK), Japan, Thailand, Philippines, Indonesia, Cambodia, Vietnam, Taiwan, Hong Kong, Mongolia and Pakistan. We identified 17 host animals and 47 species of both residential and migratory birds. Ticks from birds collected from four countries (ROK, Japan, Hong Kong and Mongolia) belonged to two genera, Haemaphysalis and Ixodes, including Haemaphysalis (H.) longicornis, H. flava, H. concinna, H. hystricis, H. formosensis, Ixodes (I.) nipponensis and I. persulcatus. The potential of migratory birds to cross ecological barriers with ticks and tick-borne diseases indicated the need for further investigations to understand the migration of birds as potential vectors and the new influx of zoonotic diseases along migratory bird flyways. This study suggests the potential risk of spreading tick-borne diseases through birds, thus highlighting the importance of international cooperative networking.

Molecular and Serological Survey of Severe Fever with Thrombocytopenia Syndrome Virus in Horses from the Republic of Korea.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic tick-borne disease in East Asia caused by the SFTS virus (SFTSV). It is to investigate the presence of SFTSV RNA and antibodies in horses from a slaughterhouse and equestrian centers in the Republic of Korea (ROK). A prevalence study of SFTSV-specific RNA and antibodies was designed from 889 horses in the ROK. Materials and Methods: Serum samples were collected from horses at a slaughterhouse and equestrian centers from 2018 to 2020. To detect the presence of SFTSV, RNA was extracted from the serum samples, and a nested reverse transcription-polymerase chain reaction (RT-PCR) was conducted. Sequencing data were analyzed, and a phylogenetic tree was constructed using the maximum-likelihood method with Molecular Evolutionary Genetics Analysis Version 7.0 software. The horse sera were also tested for SFTSV-specific immunoglobulin G antibodies using enzyme-linked immunosorbent assay (ELISA). Results: Twelve of 889 (1.3%) horse sera were positive for SFTSV RNA, and 452 of 887 (51.0%) horse sera were seropositive by ELISA. Among the RT-PCR-positive samples, 12 of the SFTSV S-segment sequences were classified as sub-genotypes B-2 (n = 6) and B-3 (n = 6). ELISA analysis was evaluated by comparison with neutralization test. We investigated SFTSV infection in horses over a 3-year period, but sampling was not performed evenly by season; continuous surveillance of SFTSV in horses is needed. Conclusions: We report the detection of SFTSV RNA and provide serological data on SFTSV prevalence in horses in the ROK. The detection of SFTSV-specific RNA and antibodies in horses, which are in close proximity to humans, suggests that SFTS is an emerging and important health issue, indicating that more attention to its relevance for equestrian workers is needed.

Serologic and Molecular Prevalence of Severe Fever with Thrombocytopenia Syndrome Virus Among Poultry in the Republic of Korea.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by Dabie bandavirus, which belongs to the genus Bandavirus, family Phenuiviridae, and order Bunyavirales. It has been found in tick species, various animals, and humans. The aim of this study was to detect RNA of antigens and antibodies against SFTS virus (SFTSV) among poultry such as chickens, ducks, and wild geese from five provinces in the Republic of Korea (ROK). Materials and Methods: A one-step reverse transcriptase (RT)-PCR and nested PCR were performed after viral RNA extraction. The phylogenetic tree was constructed after sequencing data were analyzed and aligned. An indirect enzyme-linked immunosorbent assay (ELISA) and a neutralization test (NT) were performed to test for IgG antibodies of SFTSV. Results: Of a total of 606 poultry serum samples collected, 568 and 539 serum samples were used to perform ELISA and NT, respectively. Of a total of 606 serum samples tested by RT-PCR targeting the S segment, 15 (2.5%) were positive for SFTSV. From the 15 positive serum samples for the SFTSV antigen, three from chickens, three from ducks, and one from wild geese were classified as genotype B-2; one from chickens was classified as genotype B-3; and three from chickens and four from wild geese were classified as genotype D. Of the 568 serum samples tested by ELISA, 83 (28.0%) from chickens, 81 (32.9%) from ducks, and 8 (30.8%) from wild geese were seropositive. Of the 539 serum samples for which an NT was performed, 113 (38.6%) from chickens and 75 (30.5%) from ducks were positive for SFTSV antibodies. Conclusions: The results of this study provide useful information regarding detection of SFTSV RNA and antibodies among poultry and the possibility of SFTSV transmission in various types of poultry, including chickens, ducks, and wild geese, in the ROK.

Confirmed cases of severe fever with thrombocytopenia syndrome in companion cats with a history of tick exposure in the Republic of Korea.

Severe fever with thrombocytopenia syndrome (SFTS) is a zoonotic disease, and its clinical information and prevalence are important. This study was conducted on 22 feline patients from the Republic of Korea (ROK), suspected to suffer from a tick-borne disease. Four cats were positive for SFTS, and genotypes B-1, B-3, D, and F were identified. Clinical symptoms, such as anorexia, jaundice, thrombocytopenia, leukopenia, and hyperbilirubinemia, were detected. This is the first report of SFTS virus genotypes B-1, D, and F from cats in the ROK. Moreover, our results suggest that jaundice may be an indicator of SFTS in cats.

Serological evidence of Anaplasma spp., Borrelia burgdorferi and Ehrlichia canis in dogs from the Republic of Korea by rapid diagnostic test kits.

BACKGROUND: Emergent and re-emergent canine tick-borne infections are attracting increasing attention worldwide. The rise in pet ownership and the close relationship between dogs and their owners are the most concerning factors because dogs may act as competent reservoirs for human tick-transmitted infectious agents. OBJECTIVES: This study contributes to the epidemiological surveillance of canine tick-transmitted infections with zoonotic risk in the Republic of Korea (ROK) by investigating the seroprevalence of the pathogens, Anaplasma spp., Borrelia burgdorferi, and Ehrlichia canis. METHODS: Four hundred and thirty whole blood samples from domestic dogs were collected in seven metropolitan cities and nine provinces in the ROK and tested using SensPERT Ab test kits (VetAll Laboratories®) to detect seroreactive animals. RESULTS: The seroprevalence rates identified were 9.8% (42/430) for Anaplasma spp., 2.8% (12/430) for B. burgdorferi, and 1.4% (6/430) for E. canis. The risk factors evaluated in this study that could be associated with the development of a humoral immune response, such as sex, age, and history of tick exposure, were similar. There was only one exception for dogs seroreactive to Anaplasma spp., where the risk factor "tick exposure" was statistically significant (p = 0.047). CONCLUSIONS: This serological survey exhibited the widespread presence of Anaplasma spp., B. burgdorferi, and E. canis throughout the ROK. Hence, dogs may play a key role as the sentinel animals of multiple zoonotic infectious agents in the country.

Clinical features and epidemiology of severe fever with thrombocytopenia syndrome in dogs in the Republic of Korea: an observational study (2019-2020).

Severe fever with thrombocytopenia syndrome (SFTS) is a zoonotic disease with a high mortality rate for humans and cats. The clinical course and prognosis of SFTS in dogs remains unclear. In the present study, we investigated the clinical and epidemiological characteristics of SFTS virus (SFTSV) infection in dogs. All evaluated dogs exhibited an acute course and symptoms including fever (57.1%), anorexia (57.1%), depression (42.9%), and vomiting (35.7%). Thrombocytopenia was present in 45.5% of dogs, while jaundice was not observed. C-reactive protein, alanine transaminase, and alkaline phosphatase were elevated in some cases. Viral clearance occurred within 6 to 26 days. Phylogenetic analysis revealed that the SFTSV sequences were consistent with viruses circulating in the Republic of Korea. As dogs often live in close contact with humans, awareness of the clinical and epidemiological features of SFTS in dogs is crucial. Further large-scale studies are necessary to investigate SFTSV infection in dogs.

Co-Infection with Anaplasma Species and Novel Genetic Variants Detected in Cattle and Goats in the Republic of Korea.

Anaplasmosis, a tick-borne disease with multiple reservoirs, has been evolving in its pathogenesis, increasing domestic ruminants susceptibility to simultaneous infections with multiple pathogens. However, there is limited information regarding anaplasmosis in domestic ruminants in the Republic of Korea (ROK). We aimed to evaluate the role of Korean cattle and goats in Anaplasma infection maintenance. Polymerase chain reaction was performed to investigate the prevalence and genetic diversity of Anaplasma spp. from 686 whole blood samples collected from different ROK provinces. Anaplasma infection was mostly caused by A. phagocytophilum (21.1%) in cattle, and A. bovis (7.3%) in goats. Co-infection cases were found in cattle: A. bovis and A. phagocytophilum (16.7%), and in goats: A. bovis and A. capra (1.0%). Notably, a triple co-infection with A. bovis, A. phagocytophilum, and A. capra was found in one cow. Phylogenetic analysis revealed novel variants of the A. phagocytophilum 16S rRNA and A. capra gltA genes. This research contributes to the ratification of cattle as a potential reservoir of A. capra and demonstrates Anaplasma co-infection types in Korean domestic ruminants. As anaplasmosis is a zoonotic disease, our study could be crucial in making important decisions for public health.

Survey of severe fever with thrombocytopenia syndrome virus in wild boar in the Republic of Korea.

Severe fever with thrombocytopenia syndrome (SFTS) is caused by Dabie bandavirus that belongs to the genus Bandavirus in the family Phenuiviridae and order Bunyavirales and is transmitted by hard ticks. It has been detected in several tick species, various animals, and humans. The purpose of this study was to detect SFTS virus (SFTSV) antigen and antibody in wild boar in the Republic of Korea (ROK). A total of 768 sera samples were collected from wild boar in the ROK between January and December 2019. Viral RNA was extracted from sera using viral RNA extraction kit, and one-step RT-nested polymerase chain reaction (PCR) was performed to amplify the S segment of the SFTSV. The sequencing data were analyzed using Chromas and aligned using Clustal X. The phylogenetic tree was constructed using the maximum-likelihood method using MEGA7. In addition, wild boar sera were tested for IgG antibodies against SFTSV by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assay (IFA). Of a total of 768 sera samples, 40 (5.2%) were positive for SFTSV by RT-PCR targeting the S segment. Two hundred twenty-one (28.8%) and 159 (20.7%) of 768 sera samples were seropositive by ELISA and IFA, respectively. Based on both ELISA and IFA tests of the same samples, 110 (14.3%) wild boar sera samples were positive for SFTSV antibodies. Of a total of 40 positive serum samples by RT-PCR, 33 (82.5%) and 7 (17.5%) sera were classified as the genotype B-3 and D, respectively, by sequence analysis,. These results provide useful information that demonstrates the detection of antigen and antibody in wild boar sera samples for every month of a certain year throughout the ROK.

First detection of Borrelia and Rickettsia species from Ornithodoros ticks in the Republic of Korea.

Ticks are considered important vectors among arthropods and are linked to serious medical and veterinary health problems. In this study, we investigated tick-borne pathogens (TBPs) of Ornithodoros (Carios) sawaii and a newly identified Ornithodoros species from migratory bird nests in the uninhabited islands of the Republic of Korea (ROK). Ticks were collected from seabird nests with soil using a Tullgren funnel. Polymerase chain reaction (PCR) was performed using specific primer sets targeting genes of Borrelia spp., Rickettsia sp., Anaplasma phagocytophilum, Anaplasma bovis, and Bartonella spp. for molecular identification of TBPs, and two pathogens, Borrelia sp. and Rickettsia sp. were detected via PCR. Sequence data were analyzed and a phylogenetic analysis was conducted using the maximum-likelihood method in MEGA v.7. The detection rate of Borrelia sp. in O.(C.) sawaii was 6.8 % (5/74), and that of Rickettsia sp. in O. sawaii and the newly identified Ornithodoros species. was 36.5 % (27/74). Sequencing analysis revealed that the 16S ribosomal (r) RNA and flagellin genes of Borrelia sp., and the citrate synthase (gltA) and 17-kDa antigen gene of Rickettsia sp. were closely phylogenetically related to those of Borrelia turicatae and Rickettsia asembonensis. This is the first report identifying Borrelia sp. and Rickettsia sp. from O. sawaii, and Rickettsia sp. from the newly identified Ornithodoros species in the ROK, and these results imply that soft ticks (O. sawaii, and the newly identified Ornithodoros species) may function as pathogen carriers with important implications for public health throughout their distribution areas in Asia.

Severe fever with thrombocytopenia syndrome in canines from the Republic of Korea.

Severe fever with thrombocytopenia syndrome (SFTS) in a companion dog was confirmed based on clinical symptoms, virus isolation, and virus-specific antibody detection. Fever and anorexia began after tick bite. Viremia disappeared within two weeks and antibodies were detected one week after disease onset.

Molecular and Serological Investigation of Severe Fever with Thrombocytopenia Syndrome Virus in Cats.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonosis in China, the Republic of Korea (ROK), and Japan. The presence of the SFTS virus (SFTSV) in companion, livestock, and wild animals has been reported. Recently, human SFTS-like clinical symptoms in cats and cheetahs have been reported in Japan. Therefore, the prevalence of the SFTSV gene or antibody in cats is important for public health as well as veterinary medicine. Materials and Methods: Sera were collected from 201 feral and house cats in the ROK in 2017. Samples were analyzed for the presence of the SFTSV gene after RT-nested PCR amplification and for anti-SFTSV antibodies after enzyme linked immunosorbent assay. Results: Eight (4.0%) and nine (4.5%) of 201 cat sera were found to be positive for the SFTSV gene and anti-SFTSV nucleocapsid protein antibodies, respectively. Specifically, 5.9% feral and 2.0% house cats were positive for the SFTSV gene, and 6.9% feral and 2.0% house cats were positive for anti-SFTSV antibodies. All sequences of the SFTSV S segment obtained were included in Japanese/Korean SFTSV clades, as opposed to the Chinese clade. Conclusions: This study constitutes the first serological study of SFTSV in house and feral cats in the ROK. Evidence of SFTSV in companion animals indicates that SFTSV can circulate in homes and that more intensive precautions and education measures are needed for companion animal guardians and veterinarians.

First report of Newly Identified Ornithodoros Species in the Republic of Korea.

Ticks and tick-borne diseases are important issues worldwide because of their effects on animal and human health. The genus Ornithodoros, which is included in the family Argasidae, is typically associated with wild animals, including seabirds. In this study, samples from the nests of seabirds and surrounding soil were collected to investigate Ornithodoros spp. from 9 uninhabited islands in the western, eastern, and southern parts of Korea from April 2017 to October 2018. The islands are known as the breeding places of migratory and resident birds. Ticks were collected from soil and nest material of seabirds using a Tullgren funnel and identified using 16S rRNA and the cytochrome c oxidase 1 gene (COI), and host animals of soft ticks were identified using the mitochondrial DNA cytochrome b gene by a polymerase chain reaction. In the sequence identity of the 16S rRNA gene fragment of Ornithodoros sp., Ornithodoros sawaii was identified as the closest homologous sequence, and the new Ornithodoros sp. was newly identified. We found that the newly identified Ornithodoros sp. in the Republic of Korea was located in uninhabited islands used as breeding places by the black-tailed gull, Larus crassirostris.