Seroprevalence and risk factors of severe fever with thrombocytopenia syndrome virus infection in endemic areas

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.

The ecological and etiological investigation of ticks and rodents in China: results from an ongoing surveillance study in Zhejiang Province

OBJECTIVES

This study aimed to analyze the population density of vector ticks and reservoir hosts rodents, and to investigate the relevant pathogen infection in Zhejiang Province, China.

METHODS

In this surveillance study, the data of ticks density were collected with the tick picking method on animal body surface and the drag-flag method, while the rodent density with the night trapping method. The samples of ticks were examined for the severe fever with thrombocytopenia syndrome virus (SFTSV), and blood serum and organs from rodents were subjected for SFTSV, hantavirus, Leptospira, Orientia tsutsugamushi (O. tsutsugamushi) and Yersinia pestis (Y. pestis) screening in the laboratory.

RESULTS

From 2017 to 2022 in Zhejiang Province, 16,230 parasitic ticks were found in 1848 positive animals, with the density of parasitic ticks of 1.29 ticks per host animal, and a total of 5,201 questing ticks were captured from 1,140,910 meters of vegetation distance with the questing tick density of 0.46 ticks/flag·100 m. Haemaphysalis longicornis (H. longicornis) was the major species. A total of 2,187,739 mousetraps were distributed and 12,705 rodents were trapped, with the density of 0.58 per 100 trap-nights. Rattus norvegicus was the major species. For SFTSV screening, two groups nymphal ticks of H. longicornis were tested to be positive. For the rodents samples, the Leptospira had a positive rate of 12.28% (197/1604), the hantavirus was 1.00% (16/1604), and the O. tsutsugamushi was 0.15% (2/1332). No positive results were found with SFTSV and Y. pestis in the rodents samples.

CONCLUSION

Findings from this study indicated that the ticks and rodents were widely distributed in Zhejiang Province. Particularly, the positive detection of SFTSV, Leptospira, hantavirus and O. tsutsugamushi in ticks or rodents from this area suggested that more attention should be paid to the possibilities of relevant vector-borne diseases occurrence.

Vectors, Hosts, and the Possible Risk Factors Associated with Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a disease caused by infection with the SFTS virus (SFTSV). SFTS has become a crucial public health concern because of the heavy burden, lack of vaccines, effective therapies, and high-fatality rate. Evidence suggests that SFTSV circulates between ticks and animals in nature and is transmitted to humans by tick bites. In particular, ticks have been implicated as vectors of SFTSV, where domestic or wild animals may play as the amplifying hosts. Many studies have identified antigens and antibodies against SFTSV in various animals such as sheep, goats, cattle, and rodents. Besides, person-to-person transmission through contact with blood or mucous of an infected person has also been reported. In this study, we reviewed the literature and summarized the vectors and hosts associated with SFTS and the possible risk factors.

Severe fever with thrombocytopenia syndrome virus: a systematic review and meta-analysis of transmission mode

Severe fever with thrombocytopenia syndrome (SFTS) is a disease with a high case-fatality rate that is caused by infection with the SFTS virus (SFTSV). Five electronic databases were systematically searched to identify relevant articles published from 1 January 2011 to 1 December 2019. The pooled rates with 95% confidence interval (CI) were calculated by a fixed-effect or random-effect model analysis. The results showed that 92 articles were included in this meta-analysis. For the confirmed SFTS cases, the case-fatality rate was 0.15 (95% CI 0.11, 0.18). Two hundred and ninety-six of 1384 SFTS patients indicated that they had been bitten by ticks and the biting rate was 0.21 (95% CI 0.16, 0.26). The overall pooled seroprevalence of SFTSV antibodies among the healthy population was 0.04 (95% CI 0.03, 0.05). For the overall seroprevalence of SFTSV in animals, the seroprevalence of SFTSV was 0.25 (95% CI 0.20, 0.29). The infection rate of SFTSV in ticks was 0.08 (95% CI 0.05, 0.11). In conclusion, ticks can serve as transmitting vectors of SFTSVs and reservoir hosts. Animals can be infected by tick bites, and as a reservoir host, SFTSV circulates continuously between animals and ticks in nature. Humans are infected by tick bites and direct contact with patient secretions.

Knowledge, Attitudes, and Practices regarding Severe Fever with Thrombocytopenia Syndrome in Endemic Areas of Anhui Province, Eastern China

This study aimed to assess baseline knowledge, attitudes, and practices about severe fever with thrombocytopenia syndrome (SFTS) and identify the target population for health education programs in endemic areas of Anhui, China. This cross-sectional study was conducted from May to June 2017. Of 752 participants, 383 (50.9%) were from Nanqiao District, 397 (52.8%) were female, and 430 (57.2%) were farmers; 37.4% had heard about SFTS, but knowledge of symptoms and signs including fever (34.2%), leukopenia (8.0%), and thrombocytopenia (10.1%) was low. Only 12.1% knew that SFTS virus is transmitted by ticks, 9.4% realized that the blood and body fluid of SFTS are infectious, and only 38.2% thought that the tick should be paralyzed using medical alcohol or iodine. Meanwhile, 61.3% wore long-sleeve clothes, whereas 20.2% used repellents. Median scores for knowledge, attitudes, and practices, and the total score were 4.0, 6.0, 5.0, and 16.0, respectively. Knowledge was influenced by region (OR = 0.632, 95% CI: 0.399-0.999), education (OR = 0.516, 95% CI: 0.434-0.612), gender (OR = 1.865, 95% CI: 1.165-2.987), and age (OR = 3.406, 95% CI: 2.345-4.947). Education was a predictor of lack of appreciation of infection risk (OR = 0.519, 95% CI: 0.449-0.599) and practice (OR = 0.481, 95% CI: 0.396-0.584). Our findings indicate that SFTS-related health education programs are required for females; participants from Qianshan Prefecture; those with an occupation of farmer, retiree, houseworker, or unemployed; elderly participants; and those with low education. Large-scale sustainable health education programs focusing on the target populations are urgently needed in endemic areas.

Seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) virus antibodies in humans and animals in Ehime prefecture, Japan, an endemic region of SFTS

Severe fever with thrombocytopenia syndrome (SFTS) was first identified as an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV) in China and has also been found to be endemic to Japan and South Korea, indicating that SFTS is of great concern in East Asia. The aim of the present study was to determine the seroprevalence of SFTSV antibodies in humans and animals in SFTS-endemic regions of Japan. One of 694 (0.14%) healthy persons over 50 years of age and 20 of 107 (18.7%) wild and domestic animals in Ehime prefecture of western Japan were determined to be seropositive for SFTSV antibodies by virus neutralization test and ELISA, respectively. The seropositive person, a healthy 74-year-old woman, was a resident of the southwest part of Ehime prefecture engaged in citriculture and field work. This woman's sample exhibited neutralizing activity against SFTSV although she had neither a clear experience with tick bites nor SFTS-like clinical illness. These findings indicate that most people living in the endemic regions are not infected with SFTSV and suggest that most of the SFTS patients reported so far do not reflect the tip of an iceberg of people infected with SFTSV, but at the same time, that SFTSV infection does not always induce severe SFTS-associated symptoms. These findings also suggested that SFTSV has been maintained in nature within animal species and ticks.

Characterization of clinical features and outcome for human-to-human transmitted severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease identified in 2009. SFTS is mainly transmitted by contact with ticks or animals; however, sporadic reports suggested that SFTS could be transmitted among humans.

OBJECTIVES

We aimed to comprehensively characterize clinical features and disease progression of SFTS acquired by human-to-human transmission.

STUDY DESIGN

A retrospective study of 90 SFTS patients was performed in a tertiary hospital of Nanjing, China, from October 2010 to October 2016. Seven cases of secondary SFTS were identified based on their epidemic timeline. Their clinical presentations, dynamic laboratory results and clinical outcome were analyzed.

RESULTS

First, 20 out of 83 primary SFTS patients were deceased, leading to a case-fatality ratio of 24.1%, while all secondary patients survived, suggesting a superior clinical outcome for secondary infection. Moreover, clinical symptoms and laboratory tests in primary and secondary SFTS patients were analyzed, respectively. Secondary SFTS patients developed milder clinical manifestation in the absence of neurological disorder and multiple organ failure. Further, clinical laboratory tests revealed that secondary patients had less disturbed key laboratory parameters, compared to those in primary SFTS patients. During day 7-13 post illness onset, most of the clinical laboratory results of secondary patients went back to normal range. They also had significantly lower level of viral load than primary patients.

CONCLUSIONS

Secondary SFTS acquired through human-to-human transmission leads to milder clinical representations and superior prognoses compared to primary SFTS, suggesting that the transmission route makes a difference in disease progression and clinical outcome of SFTS disease.

Estimation of the incidence of severe fever with thrombocytopenia syndrome in high endemic areas in China: an inpatient-based retrospective study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a severe viral disease caused by SFTSV. It is important to estimate the rate of missed SFTS diagnosis and to further understand the actual incidence in high endemic areas in China.

METHODS

This study was conducted in two high SFTS endemic provinces in 2015. Patients hospitalized in 2014 or within 1 year before investigation were selected after considering their clinical manifestations, specifically, fever, platelet, and white blood cell. During retrospective investigation, sera were collected to detect SFTSV antibodies to assess SFTSV infection. To further understand SFTSV infection, acute phase sera were detected; SFTSV infection rate among a healthy population was also investigated to determine the basic infection level.

RESULTS

In total, 246 hospitalized cases were included, including 83 cases (33.7%) with fever, thrombocytopenia and leukopenia, 38 cases (15.4%) with fever and thrombocytopenia but without leukopenia, and 125 cases (50.8%) without fever but with thrombocytopenia and leukopenia. In total, 13 patients (5.3%) were SFTSV IgM antibody-positive, 48 (19.5%) were IgG-positive. Of the 13 IgM-positive cases, 11 (84.6%) were IgG-positive (9 with titres ≥1:400). Seropositive rates of antibodies were high (8.4% for IgM and 30.1% for IgG) in patients with fever, thrombocytopenia and leukopenia. Furthermore, among IgG-positive cases in this group, 76% (19/25) of patients' IgG antibody titres were ≥1:400. Additionally, 28 of 246 cases were initially diagnosed with suspected SFTS and were then excluded, and 218 patients were never diagnosed with SFTS; the seropositive rates of IgM and IgG in these two groups were 25% and 67.9% and 2.8% and 13.3%, respectively. These rates were 64.3% and 21.4% in 14 sera collected during acute phase of the 28 cases mentioned above. Seropositive rate of SFTSV IgG was only 1.3% in the patient-matched healthy group, and no IgM antibody was detected. A preliminary estimate of 8.3% of SFTS cases were missed in SFTS high endemic provinces.

CONCLUSIONS

The actual SFTS incidence was underestimated. Effective measures such as adding a new SFTS case category - "SFTS clinical diagnosis cases" or using serological detection methods during acute phase should be considered to avoid missed diagnoses.

Impact of an intervention programme on knowledge, attitudes and practices of population regarding severe fever with thrombocytopenia syndrome in endemic areas of Lu'an, China

Knowledge, attitudes and practices (KAP) of the population regarding severe fever with thrombocytopenia syndrome (SFTS) in endemic areas of Lu'an in China were assessed before and after an intervention programme. The pre-intervention phase was conducted using a sample of 425 participants from the 12 selected villages with the highest rates of endemic SFTS infection. A predesigned interview questionnaire was used to assess KAP. Subsequently, an intervention programme was designed and applied in the selected villages. KAP was re-assessed for each population in the selected villages using the same interview questionnaire. Following 2 months of the programme, 339 participants had completed the re-assessed survey. The impact of the intervention programme was evaluated using suitable statistical methods. A significant increase in the KAP and total KAP scores was noted following the intervention programme, whereas the proportion of correct knowledge, the positive attitudes and the effective practices toward SFTS of respondents increased significantly. The intervention programme was effective in improving KAP level of SFTS in populations that were resident in endemic areas.

Prevalence of antibodies against severe fever with thrombocytopenia syndrome virus in shelter dogs in the Republic of Korea

The purpose of this study was to investigate the seroprevalence of antibodies against severe fever with thrombocytopenia syndrome virus (SFTSV) in shelter dogs in the Republic of Korea (ROK) using an indirect immunofluorescence assay and virus neutralization test. Sera were collected from 426 dogs in 12 animal shelters throughout the ROK from March 2016 to November 2016. Overall, 59 of 426 (13.9%) samples were seropositive for antibodies against SFTSV. A significant difference was observed in accordance with the sampling region (p<0.001), but not according to the sex (p=0.279) or breed (p=0.729) of the dogs. The seroprevalence of SFTSV showed an inversely proportional trend to the latitude of the sampling regions: the highest rate was observed in the southern region followed by the Jeju-do region. This is the first report on the nationwide prevalence of antibodies against SFTSV in companion dogs in animal shelters throughout the ROK.

Seroprevalence of severe fever with thrombocytopenia syndrome virus in China: A systematic review and meta-analysis

Objective

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a novel bunyavirus-SFTSV. The seroprevalence of anti-SFTSV antibodies including immunoglobulin G (IgG) and immunoglobulin M (IgM), specific to SFTSV in the general population has been investigated in various epidemiological studies with inconsistent results. Here, we clarify this discrepancy and reach a more comprehensive result by mean of a meta-analysis.

Methods

All relevant articles were searched in the electronic databases (PubMed, Web of science, Embase, Chinese National Knowledge Infrastructure database, Chinese Wanfang database) up to November 2016. The pooled seroprevalence and 95% confidence intervals (95% CIs) were calculated by random- or fixed- model on the basis of heterogeneity.

Results

In total, 21 studies containing 23,848 blood samples from 7 provinces were included in this meta-analysis. The minimum and maximum reported seroprevalences of SFTSV among humans in China were 0.23% and 9.17%, respectively. The overall pooled seroprevalence of SFTSV antibodies was 4.3% (95%CI: 3.2%-5.5%). The pooled prevalence was 5.9% (95%CI: 4.7%-7.0%) in Zhejiang province, 4.9% (95%CI: 4.1–5.8%) in Anhui province, 3.9% (95%CI: 1.3%-6.4%) in Shandong province, and 0.7% (95%CI: 0.2%-1.1%) in Jiangsu province. Stratified by occupation, the pooled prevalence of farmer was 6.1% (95%CI: 3.4%-8.9%) and others (mainly are students) was 3.3% (95%CI: 2.4%-4.2%). Additionally, seroprevalence of SFTSV in people who lived in the same village with the patient were higher than that of people who lived in a different village. Seropositive rates in sampling years after 2012 were higher than that before 2012. The prevalence of SFTSV did not differ by age or gender. Sensitive analysis by omitting one study at a time indicated the results of the pooled seroprevalence were robust.

Conclusions

Seroprevalence of SFTSV among healthy population in central and eastern China is high. Surveillance efforts on mild or asymptomatic infections among endemic persons are needed.

Presence of Antibodies against Severe Fever with Thrombocytopenia Syndrome Virus in Non-Endemic Areas of China

To determine the seroprevalence of severe fever with thrombocytopenia syndrome (SFTS) virus (SFTSV) and identify potential risk factors in non-endemic areas, a cross-sectional study was conducted among a healthy population without previously reported SFTS in a mountainous area of Anhui Province. We recruited and collected blood samples from 270 participants in 4 age groups. An enzyme-linked immunosorbent assay kit was used to detect immunoglobulin G (IgG) antibodies against SFTSV. The overall seropositive rate of SFTSV-IgG among study participants was 6.3% (17/270). We found a significant difference in the SFTSV seropositivity rate between tea pluckers (9.4%, 14/149) and non-tea pluckers (2.5%, 3/121). An increasing trend in the seropositivity rate was found with age for all participants (1.5% to 14.3%) and tea pluckers (2.8% to 19.4%). The SFTSV seropositivity rate in men was higher than that in women for all participants and tea pluckers, but the differences were not significant. Critical risk factors for SFTSV infection are increasing age and being a tea plucker. Our findings suggest that health education should be enhanced to increase awareness among residents (especially, the older ones and tea pluckers) to protect them against SFTS.