Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 25, Number 5—May 2019
Research Letter

Endemic Severe Fever with Thrombocytopenia Syndrome, Vietnam

Xuan Chuong Tran, Yeojun Yun, Le Van An, So-Hee Kim, Nguyen T. Phuong Thao, Phan Kim C. Man, Jeong Rae Yoo, Sang Taek Heo, Nam-Hyuk Cho, and Keun Hwa LeeComments to Author 
Author affiliations: The Hue University Hospital and Hue University of Medicine and Pharmacy, Hue, Vietnam (X.C. Tran, L.V. An, N.T.P. Thao, P.K.C. Man); Ewha Womans University, Seoul, South Korea (Y. Yun); The Kyung Hee University, Seoul (S.-H. Kim); The Jeju National University College of Medicine, Jeju, South Korea (J.R. Yoo, S.T. Heo, K.H. Lee); Seoul National University College of Medicine, Seoul (N.-H. Cho)

Cite This Article


Severe fever with thrombocytopenia syndrome (SFTS), a tickborne viral disease, has been identified in China, South Korea, and Japan since 2009. We found retrospective evidence of SFTS virus (SFTSV) infection in Vietnam, which suggests that SFTSV infections also occur in Vietnam, where the virus has not been known to be endemic.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tickborne virus (genus Phlebovirus, family Phenuiviridae) that can cause a mild to severe febrile illness similar to hemorrhagic fever (1). Phleboviruses have been found in the Americas, Asia, Africa, and the Mediterranean region. For example, Heartland virus (HRTV), another tickborne phlebovirus, was identified in northwestern Missouri, USA, in 2009 (2). Malsoor virus, a new bat phlebovirus closely related to SFTSV and HRTV, was identified in western India, and a phlebovirus similar to SFTSV and HRTV was isolated from ticks in Australia (3,4).

Severe fever with thrombocytopenia syndrome (SFTS) illness was first confirmed in China in 2009. It was retrospectively identified in South Korea in 2010 and the western regions of Japan in 2013 (1,5,6). SFTS is characterized by acute high fever, thrombocytopenia, leukopenia, elevated serum hepatic enzymes, gastrointestinal symptoms, and multiorgan failure and has a death rate of 16.2%–30% (1,6,7). Atypical signs and symptoms and asymptomatic infections also have been identified (5,8). Most SFTSV infections occur through Haemaphysalis longicornis ticks, although SFTSV transmission can also occur through close contact with an infected patient (8).

To investigate evidence of SFTSV infections in Vietnam, we collected serum samples from 80 patients with acute febrile illnesses admitted to Hue University Hospital (Hue, Vietnam) during October 1, 2017–March 31, 2018. The Institutional Review Board of Hue University Hospital approved the study.

For the molecular diagnosis of SFTSV, we extracted RNA from stored patient serum using a QIAamp Viral RNA Mini Kit (QIAGEN, and performed real-time reverse transcription PCR (rRT-PCR) to amplify the partial small (S) segment of the viral RNA from the stored serum and confirm SFTSV infection (9). rRT-PCR showed 2 positive results, from the stored serum of 2 patients with thrombocytopenia who had been seen at Hue University Hospital during 2017 and who had no history of travel to SFTSV-endemic countries, such as China, South Korea, and Japan. We also detected IgM in the serum of 1 of these patients (Appendix Table) (8).

On October 29, 2017, a 29-year-old woman (Hue 06-Vietnam-10-2017) was hospitalized at Hue University Hospital because of headache, vomiting, and gum bleeding. She lived in Hue City and was unaware of having received an insect bite. Her temperature was 38°C, and blood tests showed leukopenia (leukocyte count 1,900 cells/μL [reference 4,000–10,000 cells/μL]), thrombocytopenia (platelet count 125 × 103/μL [reference 150–450 × 103/μL]), and a low hematocrit level (34.3% [reference 36%–44%]). The patient fully recovered without other complications after 5 days.

On November 2, 2017, a 27-year-old man (Hue 13-Vietnam-11-2017) was hospitalized at Hue University Hospital because of headache and fatigue. He had had dengue fever at 8 years of age. Blood tests showed thrombocytopenia (platelet count 14 × 103/μL), normal leukocyte count (7,410 cells/μL), mildly elevated aspartate aminotransferase (84 IU/L [reference 8–38 IU/L]), elevated alanine aminotransferase (98 IU/L [reference 4–44 IU/L]), and mildly elevated hematocrit (47.6% [reference 36%–44%]). He fully recovered without other complications after 7 days.

We sequenced rRT-PCR products from the stored serum samples using a BigDye Terminator Cycle Sequencing kit (Applied Biosystems, We performed phylogenetic analysis of the partial S segment sequences with MEGA6 ( and constructed phylogenetic trees using the maximum-likelihood method, which confirmed SFTSV infection (Appendix Figure).

We confirmed 2 SFTSV infections in Hue in 2017 by amplifying the partial S segment of the viral RNA in stored serum from patients with thrombocytopenia; elevated levels of serum hepatic enzymes, including aspartate aminotransferase and alanine aminotransferase; and gastrointestinal symptoms, such as vomiting. The signs and symptoms were milder than the major signs and symptoms of SFTS, which has a high death rate.

H. longicornis, Amblyomma testudinarium, and Ixodes nipponensis ticks are vectors of SFTSV, and A. testudinarium has been found in Vietnam. Migratory birds are known to be long-distance carriers of virus-bearing ticks (10). Therefore, virus-bearing A. testudinarium ticks and migratory birds may play a role in dispersing SFTSV to Vietnam (10).

This study expands the understanding of the distribution of SFTSV in Southeast Asia and suggests that SFTSV may have a much wider global distribution than previously thought. The 2 patients reported here had relatively mild illness, and 1 did not have leukopenia. Therefore, further epidemiologic and clinical research is needed to clarify the epidemiology, geographic distribution, and transmission dynamics of SFTSV in Vietnam and other areas of Southeast Asia. This subject deserves further discussion and might warrant changes in the background description of the disease (5,8).

Dr. Tran is a professor at the Department of Infectious Diseases, Hue University Hospital and Hue University of Medicine and Pharmacy, Hue, Vietnam. His research interest is infectious diseases.



We thank L. Bakkensen for providing comments on this paper.

This work was supported by the Bio & Medical Technology Development Program of the National Research Foundation (NRF), funded by the South Korean government (grant no. NRF-2016M3A9B6021161), and a grant from the Korean Health Technology R&D Project of the Ministry of Health and Welfare, South Korea (grant no. HI15C2891).



  1. Yu  XJ, Liang  MF, Zhang  SY, Liu  Y, Li  JD, Sun  YL, et al. Fever with thrombocytopenia associated with a novel bunyavirus in China. N Engl J Med. 2011;364:152332. DOIPubMedGoogle Scholar
  2. McMullan  LK, Folk  SM, Kelly  AJ, MacNeil  A, Goldsmith  CS, Metcalfe  MG, et al. A new phlebovirus associated with severe febrile illness in Missouri. N Engl J Med. 2012;367:83441. DOIPubMedGoogle Scholar
  3. Mourya  DT, Yadav  PD, Basu  A, Shete  A, Patil  DY, Zawar  D, et al. Malsoor virus, a novel bat phlebovirus, is closely related to severe fever with thrombocytopenia syndrome virus and heartland virus. J Virol. 2014;88:36059. DOIPubMedGoogle Scholar
  4. Wang  J, Selleck  P, Yu  M, Ha  W, Rootes  C, Gales  R, et al. Novel phlebovirus with zoonotic potential isolated from ticks, Australia. Emerg Infect Dis. 2014;20:10403. DOIPubMedGoogle Scholar
  5. Kim  YR, Yun  Y, Bae  SG, Park  D, Kim  S, Lee  JM, et al. Severe tever with thrombocytopenia syndrome virus infection, South Korea, 2010. Emerg Infect Dis. 2018;24:21035. DOIPubMedGoogle Scholar
  6. Takahashi  T, Maeda  K, Suzuki  T, Ishido  A, Shigeoka  T, Tominaga  T, et al. The first identification and retrospective study of Severe Fever with Thrombocytopenia Syndrome in Japan. J Infect Dis. 2014;209:81627. DOIPubMedGoogle Scholar
  7. Li  H, Lu  QB, Xing  B, Zhang  SF, Liu  K, Du  J, et al. Epidemiological and clinical features of laboratory-diagnosed severe fever with thrombocytopenia syndrome in China, 2011-17: a prospective observational study. Lancet Infect Dis. 2018;18:112737. DOIPubMedGoogle Scholar
  8. Yoo  JR, Heo  ST, Park  D, Kim  H, Fukuma  A, Fukushi  S, et al. Family cluster analysis of severe fever with thrombocytopenia syndrome virus infection in Korea. Am J Trop Med Hyg. 2016;95:13517. DOIPubMedGoogle Scholar
  9. Zhang  YZ, He  YW, Dai  YA, Xiong  Y, Zheng  H, Zhou  DJ, et al. Hemorrhagic fever caused by a novel Bunyavirus in China: pathogenesis and correlates of fatal outcome. Clin Infect Dis. 2012;54:52733. DOIPubMedGoogle Scholar
  10. Yun  Y, Heo  ST, Kim  G, Hewson  R, Kim  H, Park  D, et al. Phylogenetic analysis of severe fever with thrombocytopenia syndrome virus in South Korea and migratory bird routes between China, South Korea, and Japan. Am J Trop Med Hyg. 2015;93:46874. DOIPubMedGoogle Scholar


Cite This Article

DOI: 10.3201/eid2505.181463

Original Publication Date: March 29, 2019

Table of Contents – Volume 25, Number 5—May 2019

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.



Please use the form below to submit correspondence to the authors or contact them at the following address:

Keun Hwa Lee, Jeju National University College of Medicine, Department of Microbiology and Immunology, 15, Aran 13-gil, Jeju 63241, South Korea

Send To

10000 character(s) remaining.


Page created: April 18, 2019
Page updated: April 18, 2019
Page reviewed: April 18, 2019
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.