Advance Publication by J-STAGE

Advance Publication by J-STAGE Japanese Journal of Infectious Diseases Low seroprevalence of severe fever with thrombocytopenia syndrome virus antibodies in individuals living in an endemic area of Japan

Mutsuyo Gokuden, Shuetsu Fukushi, Masayuki Saijo, Fumiko Nakadouzono, Yuka Iwamoto, Mami Yamamoto, Nodoka Hozumi, Kouichiro Nakayama, Kanji Ishitani, Nobuyuki Nishi, and Mitsuhiro Ootsubo

Received: November 10, 2017. Accepted: January 22, 2018. Published online: April 27, 2018. DOI: 10.7883/yoken.JJID.2017.497

Advance Publication articles have been accepted by JJID but have not been copyedited or formatted for publication.

Original article

Low seroprevalence of severe fever with thrombocytopenia syndrome

us cr ip

t

virus antibodies in individuals living in an endemic area of Japan

Mutsuyo Gokuden1, Shuetsu Fukushi2*, Masayuki Saijo2, Fumiko Nakadouzono3, Yuka Iwamoto1, Mami Yamamoto1, Nodoka Hozumi1, Kouichiro Nakayama1, Kanji Ishitani4,

1

M an

Nobuyuki Nishi5, and Mitsuhiro Ootsubo1

Kagoshima Prefectural Institute for Environmental Research and Public Health, 11-40,

2

pt ed

Kinko-cho, Kagoshima City, Kagoshima 892-0836, Japan. Department of Virology 1, National Institute of Infectious Diseases, 4-7-1 Gakuen,

Health Promotion Division of the Health and Social Welfare Department, Kagoshima

Ac

3

ce

Musashimurayama, Tokyo 208-0011, Japan.

Prefecture, 10-1 Kamoike-shinmachi, Kagoshima-shi, Kagoshima 890-8577, Japan. 4

Aira Public Health Center, Health Social Welfare and Environmental Department,

Aira-Isa Regional Promotion Bureau, 3320-16, Matsunaga Hayato-cho, Kirishima City, Kagoshima 899-5112, Japan. 1

5

Kaseda Public Health Center, Health Social Welfare and Environmental Department,

Nansatsu Regional Promotion Bureau, 1-1, Kasedamurahara, Minamisatsuma City,

us cr ip

t

Kagoshima 897-0001, Japan.

*Address Correspondence to: Shuetsu Fukushi, Ph.D. Department of Virology 1

M an

National Institute of Infectious Diseases 4-7-1 Gakuen, Musashimurayama

pt ed

Tokyo 208-0011, Japan.

TEL: +81-42-561-0771; FAX: +81-42-561-2039

Ac

ce

E-mail: [email protected]

Key words: Severe fever with thrombocytopenia syndrome (SFTS), seroprevalence, Kagoshima, ELISA, IFA, neutralization assay Running title: SFTS seroprevalence in Kagoshima, Japan

2

御供田睦代

鹿児島県鹿児島市錦江町 11 番 40 号

鹿児島県環境保健センター

東京都武蔵村山市学園 4-7-1 国立感染症研究所

西條政幸

東京都武蔵村山市学園 4-7-1 国立感染症研究所鹿児島県鹿児島市鴨池新町 10-1 鹿児島県庁保健福祉部健康増進課

us cr ip

中堂園文子

t

福士秀悦



山本真実



穂積和佳



石谷完二



鹿児島県霧島市隼人町松永 3320-16 姶良･伊佐地域振興局保健福祉

pt ed

中山浩一郎

M an

岩元由佳

環境部（姶良保健所）宣行

鹿児島県南さつま市加世田村原二丁目 1-1 南薩地域振興局保健福祉

ce

西

Ac

環境部（加世田保健所）大坪充寛


3


SUMMARY Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease

t

with a high rate of mortality. It is caused by the SFTS virus (SFTSV). SFTS is endemic

us cr ip

to western Japan, including the Kagoshima prefecture. Here, healthy persons living in Kagoshima prefecture were examined to assess the anti-SFTSV seroprevalence. An initial study was performed using serum samples collected from a total of 646 persons

M an

living in Kagoshima. At the same time, a questionnaire was used to collect information (occupation and history of being bitten by tick). An enzyme-linked immunosorbent

pt ed

assay and an indirect immunofluorescence assay were used for the screening. Finally, anti-SFTSV antibodies were confirmed in a neutralization assay. Only two persons

ce

among the 646 study participants (0.3%) were positive for anti-SFTSV antibodies.

Ac

There was no significant difference between persons with a high tick bite risk and those with a low tick bite risk in terms of seropositivity. Next, a total of 1,000 serum samples collected from general blood donors by the Japanese Red Cross Kyushu Block Blood Center were tested. None of these samples were positive for anti-SFTSV antibodies.

4

These results suggest that there is a low seroprevalence of anti-SFTSV antibodies in

Ac

ce

pt ed

M an

us cr ip

t

healthy persons living in an endemic area.

5

INTRODUCTION Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne

t

infectious disease first reported in China in 2011 (1). The disease is characterized by

us cr ip

non-specific symptoms, including fever, gastrointestinal tract symptoms, and general fatigue, and by leukopenia and thrombocytopenia. The case fatality rate (CFR) is 12% (1). SFTS is caused by infection by a novel phlebovirus, SFTS virus (SFTSV),

M an

belonging to the family Phenuiviridae (1, 2). The SFTSV genome is detected in some tick species (Haemaphysalis longicornis and Rhipicephalus microplus) living in

pt ed

epidemic areas. These ticks are the most likely vectors responsible for transmission of SFTSV to humans (1, 3). SFTS cases were also reported in South Korea in 2012 and in

ce

Japan in 2013 (4, 5). SFTS is a notifiable infectious disease, and as such 280 SFTS

Ac

patients have been reported to the National Institute of Infectious Diseases (NIID), mostly from the western part of Japan (Chugoku, Shikoku, and Kyushu regions), as of July 2017 (6). In Japan, the CFR of SFTS is approximately 20% (6). Because SFTSV is carried by mammals and ticks, people living in the SFTS-endemic area are at risk of

6

being infected. Therefore, the infection risk should be evaluated properly and greater attention should be paid to controlling SFTS in endemic areas.

t

Laboratory diagnosis of SFTS is based on detection of the SFTSV genome, on

us cr ip

isolation of SFTSV from patient blood samples and/or body fluids (e.g., throat swabs, urine), or on a significant increase in anti-SFTSV antibody titers in patients between the acute and convalescent phases (1, 7). Serological surveys based on detection of

M an

anti-SFTSV IgG antibodies in the general population provide important information about the overall picture of SFTSV infection among humans. Such data might help us to

pt ed

evaluate the ratio of symptomatic and asymptomatic infections among individuals infected with SFTSV. Furthermore, such information might shed light on the

ce

demographics and risk factor(s) for SFTSV infection in endemic areas. Despite the

Ac

simplicity and high sensitivity of antibody detection assays such as enzyme-linked immunosorbent assays (ELISAs) and immunofluorescent antibody assays (IFAs), they can give false-positive reactions. Furthermore, anti-SFTSV antibodies may cross-react with other phleboviruses present in the serum of SFTS patients during the convalescent phase (8). Therefore, the focus reduction neutralization assay (FRNA), which utilizes a

7

susceptible cell line and infectious SFTSV, is used to detect SFTSV-specific neutralizing antibodies (9). In China, a double-antigen ELISA or an indirect ELISA has

t

been used to detect anti-SFTSV IgG antibodies in the general population. Li et al. (10)

us cr ip

recently conducted a systematic review of 21 studies on SFTS seroprevalence in China. No studies have examined the seroprevalence of SFTSV in healthy persons in Japan; therefore, the risk factors associated with infection by this virus in endemic areas

M an

remain unclear. In Kagoshima prefecture (the southernmost prefecture on the island of Kyushu), more than 26 SFTS patients were identified as of July 2017 (6). Therefore, the

pt ed

aim of this study was to examine the seroprevalence of SFTSV among healthy persons in Kagoshima. Serum samples were screened using a combination of ELISA and IFA.

ce

FRNA was used to confirm whether selected samples were SFTSV antibody-positive or

Ac

-negative.

MATERIALS AND METHODS Study design and setting: A total of 646 persons participated in the initial study. From July to August 2015, blood samples were collected from members of the hunting

8

association in areas A, B, and C (Figure 1). Samples were also collected from the general population (not involved in hunting-related activities) from July 2015 to January

t

2016 in area C (Figure 1). In addition, a questionnaire was used to collect information

us cr ip

from each participant, including age, occupation (hunting-related or not), and a history of tick bites. Participants were divided into two groups: a “hunting group” (n = 125) and a “non-hunting group” (n = 521) (Table 1).

M an

Furthermore, a total of 1,000 serum samples collected from general blood donors (age range, 19–69 years) in 2016 by the Japanese Red Cross Kyushu Block Blood

pt ed

Center in Kagoshima prefecture were also included in this study. The serum samples were provided by the Japanese Red Cross Society (JRCS, Table 2). Information about the

Ac

ce

subjects (e.g., occupation and tick bite history) was not collected.

Serological testing: The IgG-ELISA was based on a viral antigen obtained from Huh7 cells infected with SFTSV (HB29 strain) as described previously (11). The cut-off optical density (O.D.) value (0.562) for 100-fold serum dilution was determined using negative control human sera (11). Serum samples with O.D. values above the cut-off

9

were subjected to IFA (11). The IFA titer was calculated as the reciprocal of the highest serum dilution at which the sample generated a specific fluorescent signal against the

t

SFTSV antigen in cells examined under a fluorescent microscope. A FRNA using the

us cr ip

SFTSV strains YG1 and HB29 was performed as described previously (9) to confirm the presence of SFTSV-neutralizing antibodies. The neutralization titer was calculated as the reciprocal of the highest serum dilution at which the number of foci was less than

M an

50% of that of the control. Serum samples that showed a positive reaction in the FRNA

pt ed

were considered anti-SFTSV antibody-positive.

Statistical analysis: Differences in the anti-SFTSV antibody prevalence between the

ce

hunting and non-hunting groups were compared using Fisher’s exact test. Statistical

Ac

analysis was performed using GraphPad Prism software (San Diego, CA).

10

RESULTS SFTS patients have been identified in many areas, including the study areas,

t

in Kagoshima prefecture. An initial study was conducted to compare anti-SFTSV

us cr ip

antibody seropositivity between healthy persons with a high tick bite risk (hunting group) and those with a low tick bite risk (non-hunting group) using a total of 646 serum samples collected from three areas in Kagoshima prefecture (Figure 1). The

M an

hunting group included members of the hunting association involved in hunting-related activities in the forest (Table 1). We used ELISA and IFA to screen samples, and a

pt ed

FRNA to confirm samples as SFTSV antibody-positive or -negative. Of the 125 participants in the hunting group, five tested positive in the IgG-ELISA. Two of these

ce

ELISA-positive subjects were also positive in the IFA (Table 2). Of the 521 participants

Ac

in the non-hunting group, seven tested positive in the IgG-ELISA and three of these were positive in the IFA (Table 2). Since most ELISA-positive sera showed O.D. values slightly higher than the cut-off O.D. value at a 100-fold dilution, the FRNA was performed to confirm the presence of anti-SFTSV antibodies in these sera. The FRNA was performed using two SFTSV strains (YG1 isolated in Japan and HB29 isolated in

11

China) to rule out the possibility that serum neutralization activity was limited to a particular virus strain. One participant in the hunting group and one in the non-hunting

t

group (Nos. 7 and 20, respectively) tested positive in the FRNA using both SFTSV

us cr ip

strains, whereas all remaining serum samples tested negative in this assay (Table 2). There was no significant difference in the rate of SFTSV antibody positivity between the hunting and non-hunting groups (p = 0.35, Table 1).

M an

Half of the participants in the non-hunting group (264/508, 52.0%) definitely recalled being bitten by a tick, whereas most of those in the hunting group (109/121,

pt ed

90.1%) reported a tick bite (p < 0.001, Table 1). There was a significant difference between the hunting and non-hunting groups in terms of the number of participants

ce

reporting multiple experiences of tick bite (p < 0.001, Table 1). There was no

Ac

statistically significant difference between the two groups in terms of onset of fever after a tick bite (p = 0.86, Table 1). The results described above indicate that only two persons (one in the hunting

group and another in the non-hunting group) among the 646 study participants (0.3%) were positive for anti-SFTSV antibodies. To examine the seroprevalence with a larger

12

number of serum samples obtained from healthy persons in Kagoshima, an additional 1,000 serum samples collected from general blood donors by the Japanese Red Cross

t

Kyushu Block Blood Center in Kagoshima prefecture were screened for the presence of

us cr ip

anti-SFTSV antibodies (Table 2). Six out of 1,000 serum samples (0.6%) showed O.D. values higher than the cut-off in the ELISA; however, none was positive in both the IFA and FRNA (Table 2), indicating that all these serum samples were negative for

M an

anti-SFTSV antibodies. Based on the aggregated data obtained in this study, only two out of 1,646 healthy subjects (0.1%) living in Kagoshima had antibodies against

Ac

ce

pt ed

SFTSV.

13

DISCUSSION Here, we examined the prevalence of anti-SFTSV antibodies in healthy

t

persons living in Kagoshima prefecture, a SFTS-endemic region of Japan. Since the

us cr ip

main route by which SFTSV infects humans is a bite by a SFTSV-carrying tick, there is an occupational risk for persons working on farms, as well as those in contact with domestic and/or wild animals (12-14). SFTSV is thought to circulate in Japan because

M an

SFTS patients are being notified (6), because the SFTSV genome is detected in several tick species, and because there is a high prevalence of anti-SFTSV antibody

pt ed

seropositivity among deer, wild boar, dogs, and raccoon dogs (15). There was a significantly higher rate of tick bites among the hunting group than among the

ce

non-hunting group (Table 1). However, we found that only two study participants (one

Ac

in the hunting group and another in the non-hunting group) were positive for SFTSV antibodies and the rate of seropositivity was similar in the two groups (Table 1 and 2). According to the questionnaire, neither of these two antibody-positive subjects developed fever after the tick bite (data not shown); therefore, we suggest that mild or asymptomatic infection is infrequent in this SFTS-endemic area of Japan.

14

The seroprevalence of anti-SFTSV antibodies in healthy persons living in Kagoshima was further examined using an additional 1,000 serum samples collected

t

from general blood donors in Kagoshima prefecture (Table 2). None of these samples

us cr ip

were positive for anti-SFTSV antibodies. Therefore, we conclude that the seroprevalence of anti-SFTSV antibodies in healthy persons living in Kagoshima prefecture is low (0.1%, 2/1,646).

M an

Similar to our findings, a previous study reported low seroprevalence (2/237, 0.8%) of SFTSV antibodies in the general population of the agricultural Yiyuan County,

pt ed

Shandong province, China, in which more than 80% of goats are anti-SFTSV antibody-positive (16). By contrast, studies conducted in SFTS-endemic regions in

ce

China reported a higher seroprevalence (more than 5%) among healthy persons (17-20).

Ac

A recent study in South Korea reported that the seroprevalence of SFTS among patients visiting a tertiary hospital was 2.1%. The reasons for these discrepancies may be explained, at least in part, by occupation, geographical location, and environmental conditions (10, 21). However, it is more likely that the higher seroprevalence reported in China and South Korea might be due to the differences in the SFTSV antibody detection

15

methods used. Previous studies used a double-antigen ELISA or an indirect ELISA to detect anti-SFTSV IgG antibodies (10, 21). By contrast, we used ELISA and IFA to

t

screen samples, and a FRNA to confirm samples as SFTSV antibody-positive or

us cr ip

-negative. An ELISA makes a rapid, sensitive, simple to perform, and easy to standardize antibody screening test; however, it may generate false-positive results (e.g., 1–2% of test samples), resulting in erroneous interpretation of seroepidemiology.

M an

Therefore, a neutralization assay is required to confirm the presence of virus-specific antibodies in serum samples (22-24).

pt ed

Among the 1,646 sera examined, 18 (1.1%) tested positive in the IgG-ELISA. However, at a dilution of 1:100, most of the ELISA-positive sera showed O.D. values

ce

slightly higher than the cut-off value (Table 2). One participant (No. 38) in the hunting

Ac

group had a high antibody titer (>640) in the IFA but tested negative in the SFTSV-FRNA. The neutralization assay is a gold-standard method for measuring serum antibody

responses

to

viral

infection;

therefore,

we

defined

neutralization

antibody-positive sera as SFTSV antibody “true-positives” and concluded that serum No. 38 was a false-positive in the ELISA and IFA.

16

It is important to note that sera obtained during the SFTS convalescent phase cross-react with Bhanja virus and Heartland virus, which are tick-borne phleboviruses

t

closely related to SFTSV (8). It is possible that this cross-reactivity among tick-borne

us cr ip

phleboviruses is due to conserved amino acids in the nucleocapsid protein, but not the glycoprotein, which is the target for neutralizing antibodies (8). Further studies are

Japan, China, or South Korea.

M an

needed to determine whether any viruses antigenically related to SFTSV are present in

Taken together, the results suggest that there is low seroprevalence of SFTS

pt ed

antibodies in healthy persons living in an endemic area, and that hunters (who have a higher risk of tick bites) have no increased risk of infection by SFTS. This study

ce

enhances understanding of the seroprevalence of anti-SFTSV antibodies in an endemic

Ac

area of Japan. Further surveillance of healthy persons living in endemic and non-endemic areas is needed to clarify the risk factor(s) associated with infection of humans with SFTSV.

17

Acknowledgments We thank Drs. Nobuyuki Mitani, Hiroshi Fukuda, Junichiro Nishi, and Koumei Shirabe

t

for help with blood sampling and testing.

us cr ip

We also thank Drs. Masayuki Shimojima, Takeshi Kurosu, Shumpei Watanabe, Hideki Tani, Satoshi Taniguchi, and Aiko Fukuma, and Ms. Momoko Ogata (Department of

Conflict of interest

M an

Virology 1, NIID), for technical support and helpful discussion.

pt ed

The authors declare no competing interests.

ce

Funding: This work was supported in part by the Japan Agency for Medical Research

Ac

and Development (AMED) and by the Ministry of Health, Labour, and Welfare (grant number H25-Shinko-Shitei-009).

Ethics statement

18

All protocols and procedures were carried out with the approval of the Research Ethics Committee of Kagoshima University, Graduate School of Medical and

t

Dental Sciences (No. 549), the Research Ethics Committee of the Kagoshima

us cr ip

Prefectural Institute for Environmental Research and Public Health (No. 28-1), and the

Ac

ce

pt ed

M an

Research Ethics Committee of the NIID (No. 626 and No. 727).

19

References 1. Yu XJ, Liang MF, Zhang SY, et al. Fever with thrombocytopenia associated with a

us cr ip

2. ICTV. Virus Taxonomy: 2016 Release, 2016.

t

novel bunyavirus in China. N Engl J Med. 2011;364:1523-1532.

3. Zhang YZ, Zhou DJ, Qin XC, et al. The ecology, genetic diversity, and phylogeny of Huaiyangshan virus in China. J Virol. 2012;86:2864-2868.

M an

4. Kim KH, Yi J, Kim G, et al. Severe fever with thrombocytopenia syndrome, South Korea, 2012. Emerg Infect Dis. 2013;19:1892-1894.

pt ed

5. Takahashi T, Maeda K, Suzuki T, et al. The first identification and retrospective study of Severe Fever with Thrombocytopenia Syndrome in Japan. J Infect Dis.

ce

2014;209:816-827.

Ac

6. NIID. National Institute of Infectious Diseases. 2017; https://www.niid.go.jp/niid/ja/sfts/3143-sfts.html. 7. Yoshikawa T, Fukushi S, Tani H, et al. Sensitive and specific PCR systems for detection of both Chinese and Japanese severe fever with thrombocytopenia syndrome

20

virus strains and prediction of patient survival based on viral load. J Clin Microbiol. 2014;52:3325-3333.

t

8. Matsuno K, Weisend C, Travassos da Rosa AP, et al. Characterization of the Bhanja

us cr ip

serogroup viruses (Bunyaviridae): a novel species of the genus Phlebovirus and its

relationship with other emerging tick-borne phleboviruses. J Virol. 2013;87:3719-28. 9. Taniguchi S, Fukuma A, Tani H, et al. A neutralization assay with a severe fever with

Methods. 2017;244:4-10.

M an

thrombocytopenia syndrome virus strain that makes plaques in inoculated cells. J Virol

pt ed

10. Li P, Tong ZD, Li KF, et al. Seroprevalence of severe fever with thrombocytopenia syndrome virus in China: A systematic review and meta-analysis. PLoS One.

ce

2017;12:e0175592.

Ac

11. Fukuma A, Fukushi S, Yoshikawa T, et al. Severe Fever with Thrombocytopenia Syndrome Virus Antigen Detection Using Monoclonal Antibodies to the Nucleocapsid Protein. PLoS Negl Trop Dis. 2016;10:e0004595.

21

12. Liang S, Bao C, Zhou M, et al. Seroprevalence and risk factors for severe fever with thrombocytopenia syndrome virus infection in Jiangsu Province, China, 2011. Am J

t

Trop Med Hyg. 2014;90:256-259.

us cr ip

13. Huang X, Zhang Z, Jin G, et al. Presence of Antibodies against Severe Fever with Thrombocytopenia Syndrome Virus in Non-Endemic Areas of China. Jpn J Infect Dis. 2017;70:248-251.

M an

14. Li Z, Hu J, Bao C, et al. Seroprevalence of antibodies against SFTS virus infection in farmers and animals, Jiangsu, China. J Clin Virol. 2014;60:185-189.

pt ed

15. IASR. 2016; 37(3) No.433. http://www.nih.go.jp/niid/en/iasr-e.html. 16. Zhao L, Zhai S, Wen H, et al. Severe fever with thrombocytopenia syndrome virus,

ce

Shandong Province, China. Emerg Infect Dis. 2012;18:963-965.

Ac

17. Zhang L, Sun J, Yan J, et al. Antibodies against severe fever with thrombocytopenia syndrome virus in healthy persons, China, 2013. Emerg Infect Dis. 2014;20:1355-1357. 18. Wei J, Li S, Dong JH, et al. The first human infection with severe fever with thrombocytopenia syndrome virus in Shaanxi Province, China. Int J Infect Dis. 2015;35:37-39.

22

19. Hu C, Guo C, Yang Z, et al. The severe fever with thrombocytopenia syndrome bunyavirus (SFTSV) antibody in a highly endemic region from 2011 to 2013: a

t

comparative serological study. Am J Trop Med Hyg. 2015;92:479-481.

us cr ip

20. Zhang L, Ye L, Ojcius DM, et al. Characterization of severe fever with

thrombocytopenia syndrome in rural regions of Zhejiang, China. PLoS One. 2014;9:e111127.

M an

21. Kim KH, Ko MK, Kim N, et al. Seroprevalence of Severe Fever with

Thrombocytopenia Syndrome in Southeastern Korea, 2015. J Korean Med Sci.

pt ed

2017;32:29-32.

22. Schwarz NG, Mertens E, Winter D, et al. No serological evidence for Zika virus

ce

infection and low specificity for anti-Zika virus ELISA in malaria positive individuals

Ac

among pregnant women from Madagascar in 2010. PLoS One. 2017;12:e0176708. 23. Rocha ES, Oliveira JG, Santos JR, et al. Recombinant envelope protein-based enzyme immunoassay for IgG antibodies is comparable to neutralization tests for epidemiological studies of dengue infection. J Virol Methods. 2013;187:114-120.

23

24. Meyer B, Drosten C, Muller MA. Serological assays for emerging coronaviruses:

Ac

ce

pt ed

M an

us cr ip

t

challenges and pitfalls. Virus Res. 2014;194:175-183.

24

Legend for figure Figure 1. Geographical locations of the study sites. Areas A, B, and C are indicated in

Ac

ce

pt ed

M an

us cr ip

t

the mainland of Kagoshima prefecture.

25

Table 1. Characteristics, SFTS seropositivity, and tick bite history of the study population Non-hunting group

Gender and age

(n=125)

(n=521)

Male

120

250

Female

5

271

p

us cr ip

t

Hunting group

Age range in years

(n=125)

(n=521)

1

32

8

134

81

270

31

63

4

22

(n=125)

(n=521)

1 (0.8%)

1 (0.2%)

Experience of tick bite

(n=121)

(n=508)

yes

109 (90.1%)

264 (52.0%)

Frequency of tick bite/year

(n=102)

(n=263)

multiple

85 (83.3%)

135 (51.3%)

< 0.001

once

7 (6.9%)

78 (29.7%)

< 0.001

at least once in recent years

10 (9.8%)

50 (19.0%)

0.04

Fever appeared after tick bite

(n=109)

(n=264)

yes

13 (11.9%)

29 (11.0%)

< 30 30–49 50–69 NR SFTSV antibodypositive

M an

> 70

0.35

Ac

ce

pt ed

Tick bite history

NR, no response.

26

< 0.001

0.86

Table 2. Detection of anti-SFTSV antibodies in serum samples from healthy persons living in Kagoshima. Neutralization titer using a specific

Non-hunting (n=521)

YG1

#7

80

20

#31

n.d.

< 5

#38

< 5

#43

n.d.

#50

n.d.

#78

< 5

#80

n.d.

#20

20

> 640

2.888

< 10

0.564

< 5

> 640

0.65

< 5

< 10

0.607

< 5

< 10

0.586

< 5

40

0.588

< 5

< 10

0.605

20

40

2.003

< 5

< 5

80

0.786

n.d.

< 5

< 10

0.723

n.d.

< 5

< 10

0.648

n.d.

< 5

< 10

1.011

#198

n.d.

< 5

< 10

0.584

#313

n.d.

< 5

< 10

1.16

#397

n.d.

< 5

< 10

0.627

#458

n.d.

< 5

< 10

0.939

#488

n.d.

< 5

< 10

1.025

#500

n.d.

< 5

< 10

0.84

#153 #214 #215

pt ed

#226

ce

(n=1,000)

Positives in each assay are highlighted in

Ac

1:100 serum dilution

HB29

t

(n=125)

IFA titer

us cr ip

Hunting

JRCS

SFTSV strain

ID

M an

Group

ELISA O.D. at

bold.

ID, identification number;

n.d., not

determined.

27

28

ce

Ac pt ed us cr ip

M an

t