Spatial epidemiological determinants of severe fever with thrombocytopenia syndrome in Miyazaki, Japan: a GWLR modeling study

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.

Evaluating the Spatial Risk of Bacterial Foodborne Diseases Using Vulnerability Assessment and Geographically Weighted Logistic Regression

Foodborne diseases are an increasing concern to public health; climate and socioeconomic factors influence bacterial foodborne disease outbreaks. We developed an “exposure–sensitivity–adaptability” vulnerability assessment framework to explore the spatial characteristics of multiple climatic and socioeconomic environments, and analyzed the risk of foodborne disease outbreaks in different vulnerable environments of Zhejiang Province, China. Global logistic regression (GLR) and geographically weighted logistic regression (GWLR) models were combined to quantify the influence of selected variables on regional bacterial foodborne diseases and evaluate the potential risk. GLR results suggested that temperature, total precipitation, road density, construction area proportions, and gross domestic product (GDP) were positively correlated with foodborne diseases. GWLR results indicated that the strength and significance of these relationships varied locally, and the predicted risk map revealed that the risk of foodborne diseases caused by Vibrio parahaemolyticus was higher in urban areas (60.6%) than rural areas (20.1%). Finally, distance from the coastline was negatively correlated with predicted regional risks. This study provides a spatial perspective for the relevant departments to prevent and control foodborne diseases.

Serological and molecular survey of tick-borne zoonotic pathogens including severe fever with thrombocytopenia syndrome virus in wild boars in Miyazaki Prefecture, Japan

Background

Miyazaki Prefecture is one of the hotspots of severe fever with thrombocytopenia syndrome (SFTS) cases and related deaths in Japan since 2013 and other pathogens of tick‐borne diseases (TBDs). Japanese spotted fever and scrub typhus are also endemic in this region.

Objectives

A total of 105 wild boars, hunted in 2009, were serologically examined as sentinels for TBDs to indirectly demonstrate the potential hazard of ticks transmitting pathogens to humans in the studied area.

Methods

The collected blood and spleens of the wild boars underwent serological and molecular tests for SFTSV, Rickettsia japonica (Rj) [antibody to spotted fever group rickettsiae (SFGR) were tested by using species‐common antigen], and Orientia tsutsugamushi (Ot).

Results

Seroprevalences of SFTSV, SFGR, and Ot were 41.9%, 29.5%, and 33.3%, respectively. SFTS viral RNA was identified in 7.6% of the sera, whereas DNA of Rj or Ot was not detected in any sample. In total, 43.8% of the boars possessed an infection history with SFTSV (viral gene and/or antibody). Of these, 23.8% had multiple‐infection history with SFGR and/or Ot.

Conclusions

The high prevalence of SFTSV in wild boars might reflect the high risk of exposure to the virus in the studied areas. In addition, SFTSV infection was significantly correlated with Ot infection, and so were SFGR infection and Ot infection, indicating that these pathogens have common factors for infection or transmission. These data caution of the higher risk of SFTSV infection in areas with reported cases of other TBDs.

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.

Isolation of Severe Fever with Thrombocytopenia Syndrome Virus from Various Tick Species in Area with Human Severe Fever with Thrombocytopenia Syndrome Cases

Severe fever with thrombocytopenia syndrome (SFTS), caused by Dabie bandavirus, generally called SFTS virus (SFTSV), is an emerging zoonosis in East Asia. In Japan, 50-100 cases of SFTS have been reported each year since the first case was reported in 2013. SFTS is a tick-borne infectious disease, and SFTSV has been isolated from ticks in China and South Korea. Haemaphysalis longicornis and Amblyomma testudinarium are considered the primary vectors in Japan. However, the other tick species seldom feeding on humans might also play an important role in maintaining the virus in nature. In this study, we collected ticks on vegetation around the location where two SFTS patients were estimated to have been infected in Miyazaki Prefecture, Japan, isolated live SFTSV, and performed a phylogenetic analysis. A total of 257 ticks were collected, and SFTSV RNA was detected in 19.5% (9/46) of tick pools. A total of 10 infectious SFTSVs were successfully isolated from A. testudinarium, Haemaphysalis flava, Haemaphysalis formosensis, Haemaphysalis hystricis, and Haemaphysalis megaspinosa. Furthermore, the whole viral sequences isolated from ticks were highly homologous to sequences isolated from SFTS patients in the same sampling area in the past. These results suggest that SFTSVs are maintained in these tick species in the sampling area and sporadically transmitted to humans. Surveillance of SFTSV in ticks provides important information about the risk of incidental transmission to humans.

Epidemic character and environmental factors in epidemic areas of severe fever with thrombocytopenia syndrome in Shandong Province

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging lethal tick-borne disease that has been widely prevalent in East Asia in recent years, and raised an important public health problem in China. However, a comprehensive and thorough understanding of the current SFTS epidemic areas in Shandong Province is not available. Accordingly, a descriptive analysis was applied to explore the demographic and spatio-temporal features of SFTS cases in Shandong Province from 2010 to 2015. The division between epidemic areas and non-epidemic areas was given by maximum entropy niche model (MaxEnt) based on environmental factors such as temperature and precipitation. There were 1,786 SFTS cases between 2010 and 2015 in Shandong, mainly involving middle-aged and elderly individuals (age:40-80) and farmers (84.6 %). May-October was the high-incidence period and the SFTS cases were mostly clustered in the central and eastern regions of Shandong Province. In light of MaxEnt, 3 specific environmental features between dichotomous areas were identified, including 1) most epidemic areas are covered by acidic soils (Constituent ratio: 63.8 %) while 29.1 % coverage appears in non-epidemic areas, 2) compared with non-epidemic areas, the identical kinds of agricultural areas accounted for a higher constituent ratio (64.9 % vs. 42.7 %), and 3) lower level of annual temperature in epidemic areas compared to non-epidemic areas [Median: 13.2℃ vs. 14.2℃; (25th IQR, 75th IQR): (12.5, 13.7) vs. (13.6, 14.9)]. Our study suggests middle-aged and elderly farmers are high-risk population to be focused on in future prevention and acidic soils, agricultural activities as well lower temperature that may be related to increased SFTS incidence.

Severe Fever with Thrombocytopenia Syndrome: Japan under Threat from Life-threatening Emerging Tick-borne Disease

Japan, like many other parts of the world, is under threat from newly emerging, potentially fatal diseases. Severe fever with thrombocytopenia syndrome (SFTS), first clinically identified in 2009, is an emerging tick-borne hemorrhagic viral disease, currently limited in distribution to East Asia. Relatively little is known about the disease with an initial Case Fatality Rate ranging from 5% to 40%. It primarily affects the elderly living in rural areas, which is particularly troublesome given Japan’s rapidly aging population. Control efforts are severely hampered by lack of specific knowledge of the disease and its means of transmission, coupled with the absence of both a vaccine and an effective treatment regime, although some antiviral drugs and blood transfusions are successful in treating the disease. Despite both the causative virus and vector ticks being commonly found throughout Japan, the disease shows a very specific, limited geographical distribution for as yet unknown reasons.