Hedgehogs are the major amplifying hosts of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne bandavirus mainly transmitted by Haemaphysalis longicornis in East Asia, mostly in rural areas. To date, the amplifying host involved in the natural transmission of SFTSV remains unidentified. Our epidemiological field survey conducted in endemic areas in China showed that hedgehogs were widely distributed, had heavy tick infestations, and had high SFTSV seroprevalence and RNA prevalence. After experimental infection of Erinaceus amurensis and Atelerix albiventris hedgehogs with SFTSV, robust but transitory viremias were detected, which lasted for around nine to eleven days. The infected hedgehogs experienced light weight loss and histopathology of the spleen showed hemorrhagic necrosis and lymphopenia, with infected hedgehogs recovering after viral clearance. Remarkably, SFTSV transmission cycle between hedgehogs and nymph/adult H. longicornis was easily accomplished under laboratory condition with 100% efficiency. Furthermore, naïve H. longicornis ticks could be infected by SFTSV-positive ticks co-feeding on naïve hedgehogs, with transstadial transmission of SFTSV also confirmed. We also found that SFTSV viremia remained high in hedgehogs during hibernation, suggesting that this mechanism might contribute to the persistence of SFTSV from one year to the next. Of concern, we recently found evidence of the natural circulation of SFTSV in the urban area of Beijing City in China involving H. longicornis ticks and E. amurensis hedgehogs. Our study suggests that the hedgehogs are the major wildlife amplifying hosts of SFTSV and that urban outbreaks of SFTSV might occur in the future.

Island, 28% of the captured small mammals were E. amurensis (Amur hedgehog), 18% were 144 Rattus. Norvegicus (brown rat), 36% were Sorex araneus (common shrew), and 18% were 145 Apodemus agrarius (striped field mouse). On Xiushan Island no hedgehogs were caught, 48% of 146 the small mammals caught were R. norvegicus, 44% were S. araneus and 8% were Rattus losea 147 (lesser ricefield rat) (Fig. 1C). Antibody testing showed that 3/9 (33%) of E. amurensis hedgehogs 148 from Daishan Island were positive for SFTSV (Fig. 1D). Hedgehogs are abundant in the two 149 villages in Daishan Island, with an estimated population density of greater than 80 individuals per 150 square kilometer based on the results of the trapping study (Table 1). In addition, these nine 151 trapped hedgehogs were all heavily infected by ticks with an average of 145 ticks per hedgehog,

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Neutralizing antibody titer against SFTSV in the sera of two E. amurensis hedgehogs were

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There was a possibility that the observed weight loss could have been iatrogenic, since the blood 215 samples were taken directly from the heart. Heart sampling was necessary because rapid blood 216 coagulation makes sampling from superficial veins very difficult in hedgehogs (Lewis, 1976). To 217 test whether heart sampling was the cause of the weight loss, a further six A. albiventris were i.p.

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inoculated with SFTSV as above and bled only twice on d 7 and d 14, instead of daily. We found 219 that only one hedgehog showed a weight loss of 20% and recovered by d 16 (Fig. S1A). In these 220 six hedgehogs, SFTSV viremia was detected at d 7 and disappeared at d 14 (Fig. S1B)

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To assess the pathological changes in hedgehogs resulting from SFTSV infection, six A. 295 longicornis ticks were prepared as described above with 100% efficiency (Fig. 5A and 5B). 299 The viral load in the engorged nymphs and previously naïve adults were 2.5 and 2.7 log10 RNA 300 copies/mg tick respectively ( Fig. 5C and 5D). After the nymphs molted, the adult ticks tested

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100% positive for SFTSV, with a level of 6.9 log10 RNA copies/mg tick (Fig. 5E). Thus, these 302 results suggest that hedgehogs could be acting as an amplifying host for SFTSV.

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It's still plausible that other animals or birds could also maintain the natural circulation of SFTSV.

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To conclude that hedgehogs are the major amplifying hosts of SFTSV in the real world,   hedgehogs were introduced to New Zealand by human intervention ISAAC, 2005).

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In conclusion, our data strongly support our initial hypothesis that hedgehogs can maintain the

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Serum samples from animals were tested for SFTSV antibodies including IgG and IgM with a 493 commercial double antigen sandwich ELISA kit from Nanjing Immune-detect Bio-tech Co., Ltd.

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(Jiangsu, China). were performed and selected sections were stained with H&E for light microscopy examination.

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Images were obtained using a Nikon Eclipse 50i Light Microscope (Nikon, Tokyo, Japan) or

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The authors declare no competing interests.

Fig. S3
Seroprevalence of SFTSV in all hedgehogs prior to experimental infection. The serum samples were tested for SFTSV IgG and IgM antibodies prior to experimental infection with a commercial double antigen sandwich ELISA kit. Cutoff = 0.748×Negative OD +0.146. Red dot indicates positive sample, green dot indicates negative sample and gray dot indicates blank control.