Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever in East Asia caused by SFTS virus (SFTSV), a newly discovered phlebovirus. The Haemaphysalis longicornis tick has been suspected to be the vector of SFTSV. To determine whether SFTSV can be transmitted among ticks, from ticks to animals, and from animals to ticks, we conducted transmission studies between developmental stages of H. longicornis ticks and between ticks and mice. Using reverse transcription PCR, we also analyzed the prevalence of SFTSV infection among H. longicornis ticks collected from vegetation in Shandong Province, China. Our results showed a low prevalence of SFTSV among collected ticks (0.2%, 8/3,300 ticks), and we showed that ticks fed on SFTSV-infected mice could acquire the virus and transstadially and transovarially transmit it to other developmental stages of ticks. Furthermore, SFTSV-infected ticks could transmit the virus to mice during feeding. Our findings indicate ticks could serve as a vector and reservoir of SFTSV.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a newly discovered bunyavirus, SFTS virus (SFTSV), and causes high fatality (12% on average and as high as 30%). The objective of this study was to determine whether SFTSV could be transmitted from person to person. We analyzed sera of 13 patients from two clusters of unknown infectious diseases that occurred between September and November of 2006 in Anhui Province of China for SFTSV antibody by indirect immunofluorescence assay and for SFTSV RNA by RT-PCR. We found that all patients ( n =14) had typical clinical symptoms of SFTS including fever, thrombocytopenia, and leukopenia and all secondary patients in both clusters got sick at 6–13 days after contacting or exposing to blood of index patients. We demonstrated that all patients in cluster 1 including the index patient and nine secondary patients and all three secondary patients in cluster 2 had seroconversion or fourfold increases in antibody titer to SFTSV and/or by RT-PCR amplification of SFTSV RNA from the acute serum. The index patient in cluster 2 was not analyzed because of lack of serum. No person who contacted the index patient during the same period, but were not exposed to the index patient blood, had got illness. We concluded that SFTSV can be transmitted from person to person through contacting patient's blood.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly discovered Phlebovirus causing an emerging hemorrhagic fever in East Asia, with reported case fatality rates up to 30%. Despite the high case fatality rate and large number of persons at risk of infection, the pathobiology of the disease is unknown, and no effective animal model has been available for investigating its pathogenesis. We have studied mice and hamsters as potential small-animal models of SFTSV infection following subcutaneous, intraperitoneal, or intracerebral inoculation. Animal tissues were processed for viral load determination, histopathology, immunohistochemistry, and confocal microscopic studies. We found that immunocompetent adult mice and hamsters did not become ill after SFTSV infection. However, alpha/beta interferon receptor knockout (IFNAR ^−/− ) mice were highly susceptible to SFTSV infection, and all mice died within 3 to 4 days after subcutaneous inoculation of 10 ⁶ focus-forming units of SFTSV. Histologic examination of tissues of IFNAR ^−/− mice infected with SFTSV showed no detectable lesions. In contrast, by immunohistochemistry virus antigen was found in liver, intestine, kidney, spleen, lymphoid tissue, and brain, but not in the lungs. Mesenteric lymph nodes and spleen were the most heavily infected tissues. Quantitative reverse transcription-PCR (RT-PCR) confirmed the presence of virus in these tissues. Confocal microscopy showed that SFTSV colocalized with reticular cells but did not colocalize with dendritic cells, monocytes/macrophages, neutrophils, or endothelium. Our results indicate that SFTSV multiplied in all organs except for lungs and that mesenteric lymph nodes and spleen were the most heavily infected tissues. The major target cells of SFTSV appear to be reticular cells in lymphoid tissues of intestine and spleen.

Severe fever with thrombocytopenia syndrome, which results in severe illness and has a high case-fatality rate, is caused by a novel bunyavirus, severe fever with thrombocytopenia syndrome virus. We found that samples from 2/237 (0.8%) healthy persons and 111/134 (83%) goats in Yiyuan County, Shandong Province, China, were seropositive for this virus.