Lethal Disease in Dogs Naturally Infected with Severe Fever with Thrombocytopenia Syndrome Virus

Prevalence, Isolation, and Molecular Characterization of 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.

Severe fever with thrombocytopenia syndrome (SFTS) in Thailand: using a one health approach to respond to novel zoonosis and its implications in clinical practice

Severe fever with thrombocytopenia syndrome (SFTS), a tick-borne disease caused by Dabie bandavirus (SFTSV) is an emerging infectious disease of substantial concern in East Asia. In 2019, Ongkittikul S et al. reported the first case of SFTS in Thailand. Our report describes a One Health investigation of SFTS zoonosis examining the index case and suspected animal reservoirs using real-time RT-PCR and immunoassays. We add to the report on the first confirmed case of SFTSV infection in a human in Thailand by conducting a limited but informative One Health surveillance study. Dogs and cats tested positive for SFTSV antibody using IgG ELISA. We conclude that domestic dogs and cats might serve as potential reservoirs for SFTSV spread due to their closer proximity to the index case than other non-domestic animals. Notably, we did not detect SFTSV in synanthropic cats or dogs-nor did we detect SFTSV in Rhipicephalus sanguineus ticks-using RT-PCR. We propose that One Health investigations coupling genomic and serologic assays in response to new SFTS cases could play a pivotal role in preventing and managing SFTS among humans and animals in East Asia. As such, we are establishing a collaborative response to SFTS in Thailand through human outbreak investigations that align with principles of One Health, through environmental surveys and animal RT-PCR and immunoassays. Our investigation highlights the importance of coupling RT-PCR with seroprevalence assays as principal elements of One Health surveillance for SFTS in order to shed light on potential animal reservoirs and track emerging zoonosis.

Characterization and arbovirus susceptibility of cultured CERNI cells derived from sika deer (Cervus nippon)

Cervus nippon (sika deer) are widely distributed throughout eastern Asia. Deer possess a variety of antibodies against several zoonotic pathogens, indicating that they act as reservoir of zoonoses. In this study, we reported the characterization of cultured cells derived from sika deer and evaluated their susceptibility to arthropod-borne viruses to clarify their usefulness in virological studies. Cells derived from testicular tissue in Dulbecco's modified eagle medium with 16% fetal bovine serum started growing as primary cultured cells. The diploid cells consisted of 68 chromosomes, consistent with those of Japanese sika deer previously reported. The phylogenetic analysis showed the cells formed a robust clade with Japanese population of C. nippon, indicating that the cultured cells established in this study were originated from the Japanese sika deer. The cells immortalized by the simian virus 40 T-antigen were predominantly spindle-shaped cells exhibiting adhesive properties, and cultivated at 37°C and 5% CO2, which are common culture conditions for many mammalian cell lines. Western blotting analysis indicated that the cultured cells were multiple types of cells that coexist, including at least epithelial, fibroblast, and also Leydig cells. We confirmed that the cells have susceptibility to several arboviruses distributed in Japan: Getah virus, Japanese encephalitis virus, Oz virus, and severe fever with thrombocytopenia syndrome virus, but not to Tarumiz tick virus. From these results, the cells contribute to clarify the role of sika deer as a reservoir of zoonoses in nature and deer-associated experimental research at the cellular and molecular levels.

Seroprevalence for severe fever with thrombocytopenia syndrome virus among the residents of Miyazaki, Japan: An epidemiological study

INTRODUCTION

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease caused by the SFTS virus (SFTSV). The Miyazaki Prefecture has the highest number of SFTS cases in Japan and requires countermeasures for prevention. In this study, we aimed to conduct an epidemiological survey in Miyazaki Prefecture to determine the exposure conditions of SFTSV by measuring the seroprevalence among residents of Miyazaki and to evaluate the factors that influence the endemicity of SFTS.

METHODS

The survey was conducted between June 2014 and April 2019 in all 26 municipalities in Miyazaki Prefecture. SFTSV antibodies were detected using an enzyme-linked immunosorbent assay in the blood samples of 6013 residents (3184 men and 2829 women). A questionnaire-based survey of the living environment was also conducted.

RESULTS

Multiple logistic regression analysis revealed that age and occupation were significant factors related to the proportion of participants with an optical density (OD) value > 0.2 and a seroprevalence of 0.9 % (54/6013). Seven seropositive individuals (0.1 %) with an OD value of >0.4 were identified (three men and four women, aged 54-69 years), and all were asymptomatic. One participant had a higher OD than the positive control.

CONCLUSION

Although SFTS is endemic in Miyazaki Prefecture, Japan, its seroprevalence is relatively low. Since some risk areas in Miyazaki prefecture have been identified, it is important to enhance awareness of SFTS in residences and reduce contact with ticks, especially in high-risk areas.

Nine-year seroepidemiological study of severe fever with thrombocytopenia syndrome virus infection in feral horses in Cape Toi, Japan

Severe fever with thrombocytopenia syndrome (SFTS) is a fatal zoonosis caused by ticks in East Asia. As SFTS virus (SFTSV) is maintained between wildlife and ticks, seroepidemiological studies in wildlife are important to understand the behavior of SFTSV in the environment. Miyazaki Prefecture, Japan, is an SFTS-endemic area, and approximately 100 feral horses, called Misaki horses (Equus caballus), inhabit Cape Toi in Miyazaki Prefecture. While these animals are managed in a wild-like manner, their ages are ascertainable due to individual identification. In the present study, we conducted a seroepidemiological survey of SFTSV in Misaki horses between 2015 and 2023. This study aimed to understand SFTSV infection in horses and its transmission to wildlife. A total of 707 samples from 180 feral horses were used to determine the seroprevalence of SFTSV using enzyme-linked immunosorbent assay (ELISA). Neutralization testing was performed on 118 samples. In addition, SFTS viral RNA was detected in ticks from Cape Toi and feral horses. The overall seroprevalence between 2015 and 2023 was 78.5% (555/707). The lowest seroprevalence was 55% (44/80) in 2016 and the highest was 92% (76/83) in 2018. Seroprevalence was significantly affected by age, with 11% (8/71) in those less than one year of age and 96.7% (435/450) in those four years of age and older (p < 0.0001). The concordance between ELISA and neutralization test results was 88.9% (105/118). SFTS viral RNA was not detected in ticks (n = 516) or feral horses. This study demonstrated that horses can be infected with SFTSV and that age is a significant factor in seroprevalence in wildlife. This study provides insights into SFTSV infection not only in horses but also in wildlife in SFTS-endemic areas.

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.

Elucidation of prognostic factors in the acute phase of feline severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal tick-borne zoonotic disease, endemic to Asian regions, including western Japan. Cats appear to suffer a particularly severe form of the disease; however, feline SFTS is not clinically well characterized. Accordingly, in this study, we investigated the associations of, demographic, hematological and biochemical, immunological, and virological parameters with clinical outcome (fatal cases vs. survivors) in SFTSV-positive cats. Viral genomic analysis was also performed. Viral load in blood, total bilirubin, creatine phosphokinase, serum amyloid A, interleukin-6, tumor necrotic factor-α, and virus-specific IgM and IgG differed significantly between survivors and fatal cases, and thus may have utility as prognosticators. Furthermore, survivor profiling revealed high-level of viremia with multiple parameters (white blood cells, platelet, total bilirubin, glucose, and serum amyloid A) beyond the reference range in the 7-day acute phase, and signs of clinical recovery in the post-acute phase (parameters returning to, or tending toward, the reference range). However, SFTSV was still detectable from some survived cats even 14 days after onset of disease, indicating the risk of infection posed by close-contact exposure may persist through the post-acute phase. This study provides useful information for prognostic assessments of acute feline SFTS, and may contribute to early treatment plans for cats with SFTS. Our findings also alert pet owners and animal health professionals to the need for prolonged vigilance against animal-to-human transmission when handling cats that have been diagnosed with SFTS.

High Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Infection among the Dog Population in Thailand

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonotic disease caused by the SFTS virus (SFTSV). In Thailand, three human cases of SFTS were reported in 2019 and 2020, but there was no report of SFTSV infection in animals. Our study revealed that at least 16.6% of dogs in Thailand were seropositive for SFTSV infection, and the SFTSV-positive dogs were found in several districts in Thailand. Additionally, more than 70% of the serum samples collected at one shelter possessed virus-neutralization antibodies against SFTSV and the near-complete genome sequences of the SFTSV were determined from one dog in the shelter. The dog SFTSV was genetically close to those from Thailand and Chinese patients and belonged to genotype J3. These results indicated that SFTSV has already spread among animals in Thailand.

Epidemiology of Severe Fever with Thrombocytopenia Syndrome in Dogs and Cats in Taiwan

Severe Fever with Thrombocytopenia Syndrome (SFTS), caused by the SFTS Virus (SFTSV), is a global health threat. SFTSV in Taiwan has only been reported in ruminants and wild animals. Thus, we aimed to investigate the infection statuses of dogs and cats, the animals with closer human interactions. Overall, the SFTSV RNA prevalence was 23% (170/735), with dogs showing a 25.9% (111/429) prevalence and cats at 19.3% (59/306) prevalence. Noticeably, the prevalence in stray animals (39.8% 77/193) was significantly higher than in domesticated ones (17.2%, 93/542). Among the four categories analyzed, the highest SFTSV prevalence was found in the stray dogs at 53.9% (120/193), significantly higher than the 24.2% prevalence noted in stray cats. In contrast, domesticated animals exhibited similar prevalence rates, with 17.1% for dogs and 17.2% for cats. It is noteworthy that in the domesticated animal groups, a significantly elevated prevalence (45%, 9/20) was observed among cats exhibiting thrombocytopenia compared to those platelet counts in the reference range (4.8%, 1/21). The high infection rate in stray animals, especially stray dogs, indicated that exposure to various outdoor environments influences the prevalence of infections. Given the higher human interaction with dogs and cats, there is a need for proactive measures to reduce the risk associated with the infection of SFTSV in both animals and humans.

Long-Term Detection and Isolation of Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus in Dog Urine

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection caused by the SFTS virus (SFTSV), with a high fatality rate of approximately 30% in humans. In recent years, cases of contact infection with SFTSV via bodily fluids of infected dogs and cats have been reported. In this study, clinical and virological analyses were performed in two dogs in which SFTSV infection was confirmed for the first time in the Toyama prefecture. Both dogs recovered; however, one was severely ill and the other mildly ill. The amount of the SFTSV gene was reduced to almost similar levels in both dogs. In the dogs' sera, the SFTSV gene was detected at a low level but fell below the detection limit approximately 2 weeks after onset. Notably, the SFTSV gene was detected at levels several thousand times higher in urine than in other specimens from both dogs. Furthermore, the gene was detected in the urine for a long period of >2 months. The clinical signs disappeared on days 1 or 6 after onset, but infectious SFTSV was detected in the urine up to 3 weeks later. Therefore, it is necessary to be careful about contact with bodily fluids, especially urine, even after symptoms have disappeared.

Advancements in the Worldwide Detection of Severe Fever with Thrombocytopenia Syndrome Virus Infection from 2009 to 2023

Severe fever with thrombocytopenia syndrome (SFTS) is a growing concern as an emerging tick-borne infectious disease originating from the SFTS virus (SFTSV), a recent addition to the Phlebovirus genus under the family of bunyaviruses. SFTS is typically identified by symptoms such as fever, thrombocytopenia, leukopenia, and gastrointestinal problems, accompanied by a potentially high case fatality rate. Thus, early and accurate diagnosis is essential for effective treatment and disease management. This review delves into the existing methodologies for SFTS detection, including pathogenic, molecular, and immunological technologies.

Carbon black as a colorimetric label for an immunochromatographic test strip for severe fever with thrombocytopenia syndrome virus detection

To combat the ongoing threat posed by severe fever with thrombocytopenia syndrome virus (SFTSV), especially in underserved areas, there is an urgent need for an affordable and reliable point-of-care diagnostic tool. This study presents a carbon black-based immunochromatographic test strip (CB-ICTS) for the detection of SFTSV, which is both quick and easy to operate. The study optimized the specific steps for carbon black-labeled antibodies, as well as the amount of carbon black and anti-SFTSV antibody used. Under optimal experimental conditions, the linear range and limit of detection of the CB-ICTS were evaluated using different concentrations of SFTSV standard samples. The detection range of the CB-ICTS for SFTSV was found to be 0.1-1000 ng mL^-1, with a limit of detection of 100 pg mL^-1. The precision and accuracy of the CB-ICTS were assessed by examining spiked healthy human serum samples, which displayed recoveries ranging from 91.58 to 105.4% with a coefficient of variation of less than 11%. This work evaluated the specificity of the CB-ICTS using various biomarkers (CA125, AFP, CA199, CEA, and HCG) and demonstrated that the CB-ICTS is highly specific for detecting SFTSV, suggesting its potential for the early diagnosis of SFTSV. In addition, the study evaluated the CB-ICTS in serum samples from patients with SFTSV, and the results were highly consistent with those detected by the polymerase chain reaction (PCR) method. Overall, this study demonstrates the feasibility and effectiveness of using the CB-ICTS as a reliable point-of-care diagnostic tool for the early detection of SFTSV.

Increased Risk of Infection with Severe Fever with Thrombocytopenia Virus among Animal Populations on Tsushima Island, Japan, Including an Endangered Species, Tsushima Leopard Cats

To investigate the seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) among wild and companion animals on Tsushima Island, Japan, SFTS virus (SFTSV)-specific ELISA and virus-neutralizing tests were conducted on 50 wild boars, 71 Sika deer, 84 dogs, 323 domestic cats, and 6 Tsushima leopard cats. In total, 1 wild boar (1.8%), 2 dogs (2.4%), 7 domestic cats (2.2%), and 1 Tsushima leopard cat (16.7%) were positive for anti-SFTSV antibodies. Among the 11 positive animals, 10 were collected after 2019, and all were found on the southern part of the island. SFTSV, thus far, seems to be circulating within a limited area of Tsushima Island. To protect humans and animals, including endangered Tsushima leopard cats, from SFTSV infection, countermeasures are needed to prevent the spread of SFTSV on Tsushima Island.