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 17, Number 5—May 2011

Japanese Encephalitis, Tibet, China

On This Page
Article Metrics
citations of this article
EID Journal Metrics on Scopus

Cite This Article

To the Editor: Tibet is located in the Qinghai-Tibet Plateau of western People’s Republic of China and has been internationally recognized as a Japanese encephalitis (JE)–nonendemic area because the average altitude is thought to be too high to facilitate the cycle of Japanese encephalitis virus (JEV) between mosquitoes and vertebrates (1,2). In addition, JE is a reportable infectious disease in China, and no clinically confirmed case has been reported in Tibet since establishment of a national case reporting system in 1951 (3,4). Neither the mosquito vector of JEV nor JEV isolates have been described in Tibet. In this study, JEV was isolated from Culex tritaeniorhynchus mosquitoes, the main vectors of JEV, collected in Tibet. Serologic assays detected anti-JEV antibodies in a large number of human and porcine serum samples collected in this region. These data demonstrate that JEV is currently circulating in Tibet.

During August 5–15, 2009, mosquitoes were collected in Mainling County (altitude 2,900 m) and Medog County (altitude 1,000 m) in the Nyingchi area of Tibet. A total of 4,089 mosquitoes representing 7 species (Cx. tritaeniorhynchus, Cx. pipiens pallens, Cx. bitaeniorhynchus, Armigeres obturbans, Anopheles maculatus maculates, An. peditaeniatu, and Aedes albopictus) from 4 genera were collected in this study. The dominant mosquito species detected in Medog County was Cx. tritaeniorhynchus (2,442 [71.1%] of 3,436 mosquitoes collected there) (Table); no previous reports have described this species in Tibet. A total of 653 mosquitoes were collected in Mainling County, of which 489 (74.9%) were Armigeres obturban. No Cx. tritaeniorhynchus mosquitoes were collected in Mainling County.

Mosquitoes were homogenized in 97 pools by using TissueLyser (QIAGEN, Hilden, Germany) and screened with reverse transcription–PCR (RT-PCR) by using seminested primers designed to detect the JEV PreM gene (5). One Cx. tritaeniorhynchus pool, XZ0938, collected in Medog County was positive by PCR. Isolation of virus was conducted from PCR-positive sample by injecting mosquito homogenate supernatants into monolayers of BHK-21 and C6/36 cells. The supernatant of pool XZ0938 caused cytopathic effects in BHK-21 and C6/36 cells in successive cell passages. The complete genome of 10,965 nt was sequenced (GenBank accession no. HQ652538) as described (6), which included a 96-nt 5′ nontranslated region and a 570-nt 3′ nontranslated region. The single open reading frame coded for a polyprotein of 3,432 aa. Compared with the complete genome sequences of 62 known JEV isolates, the nucleotide sequence identity varied from 83.6% to 97.8% and amino acid sequence identity from 94.9% to 99.7%. Phylogenetic trees derived from nucleotide sequences of the complete genome of JEV strains indicated that XZ0938 was a member of genotype I JEV. A more detailed analysis indicated that the Tibet JEV is most closely related to JEV isolates KV1899 (1999, Korea, AY316157), and JEV/sw/Mie/41/2002 (2002, Japan, AB241119) (data not shown).

To determine whether local residents were infected by JEV, 248 human serum samples were collected in Mainling and Medog Counties from healthy persons. Neutralizing antibody against JEV was tested by 90% plaque-reduction neutralization tests by using standard methods (7). Serum samples were tested with serial 2-fold dilutions from 1 to 5. Diluted serum was mixed with equal volumes of culture medium containing JEV P3 strain. The samples were considered positive when the neutralizing antibody titers >10. Sixty-eight positive samples were determined by 90% plaque-reduction neutralization tests, which constituted 68 (27.4%) of all 248 serum samples. Twenty-two (22.0%) of 100 and 46 (31.1%) of 148 serum samples in Mainling and Medog Counties, respectively, were positive (Table). Currently, the local population is not vaccinated against JEV (8) because Tibet is considered a JE-nonendemic area (14). The observation that 68 (27.4%) of 248 serum samples from healthy humans contained neutralizing antibody against JEV at titers >10 suggests that this population is subject to substantial levels of subclinical JEV infection.

To determine the present situation of JEV infection in local pigs, we analyzed 66 serum samples collected from piglets 1–6 months of age in Mainling and Medog Counties; immunoglobulin M antibodies against JEV were detected by capture ELISA as described (9). That 22 (33.3%) of 66 piglet serum samples were positive for immunoglobulin M against JEV suggested that local pigs have been newly infected by JEV in 2009 and have participated in the cycles of JEV in the local area (Table).

JE is a global public health issue that has spread to >20 countries in Asia (6,10). In this study, we present evidence that JEV has extended its geographic range to Tibet, a region that previously was believed to be free of JE because of its elevation. Factors such as global warming, increased pig farming, and increased tourism and transportation may have contributed to the emergence of JE in Tibet. Conditions in Tibet, including the presence of the primary vector (Cx. tritaeniorhynchus mosquitoes), abundant amplification hosts (pig), and a naive population that has not been vaccinated against JEV, present the possibility for JE outbreaks. Increased surveillance for JE in this region is needed.



We thank David Wang for consultation and assistance in preparing and writing this manuscript.

This work was supported by grants from the Ministry of Science and Technology, China (2003BA712A08-01; 2008ZX10004-001; 2011CB504702); China-US CDC Cooperative Agreement U19-GH000004; and Development Grant of State Key Laboratory for Infectious Disease Prevention and Control (2008SKLID105).


Yi-Xing Li1, Ming-Hua Li1, Shi-Hong Fu, Wei-Xin Chen, Qi-Yong Liu, Hai-Lin Zhang, Wa Da, Song-Lin Hu, Sang Dan La Mu, Ju Bai, Zun-Dong Yin, Hong-Yue Jiang, Yu-Hong Guo, Dun Zhu Duo Ji, Hui-Mei Xu, Ge Li, Gu Gu Cuo Mu, Hui-Ming Luo, Jing-Lin Wang, Jun Wang, Xiu-Min Ye, Zhuo Ma Yang Jin, Wei Zhang, Gui-Jun Ning, Huan-Yu Wang, Gui-Chang Li, Jian Yong, Xiao-Feng Liang, and Guo-Dong LiangComments to Author 
Author affiliations: Author affiliations: National Immunization Programme, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China (Y.-X. Li, Z.-D. Yin, H.-M. Luo, G.-J. Ning, X.-F. Liang); Institute for Viral Disease Control and Prevention, Beijing (M.-H. Li, S.-H. Fu, W.-X. Chen, H.-Y. Jiang, J.-L. Wang, H.-Y. Wang, G.-D. Liang); National Institute for Communicable Disease Control and Prevention, Beijing (Q.-Y. Liu, Y.-H. Guo, J. Wang, G.-C. Li); Yunnan Institute of Endemic Disease Control and Prevention, Yunnan, People’s Republic of China (H.-L. Zhang); Tibet Center for Disease Control and Prevention, Tibet, People’s Republic of China (W. Da, D.Z.D. Ji, X.-M. Ye); Nyingchi Center for Disease Control and Prevention, Tibet (S.-L. Hu, H.-M. Xu, Z.M.Y. Jin); Medog County Center for Disease Control and Prevention, Tibet, (S.D.L. Mu, G. Li, W. Zhang, J. Yong); Mainling County Center for Disease Control and Prevention, Tibet (J. Bai, G.G.C. Mu)



  1. International Travel and Health. Infectious diseases of potential risk for travelers. Geneva: World Health Organization; 2010.
  2. Brunette  GW, Kozarsky  PE, Magill  AJ, Shlim  DR. The pre-travel consultation. In: CDC health information for international travel, 2010 (the yellow book). New York: Elsevier; 2009. p. 19–241.
  3. Gao  X, Nasci  R, Liang  G. The neglected arboviral infections in mainland China. PLoS Negl Trop Dis. 2010;4:e624. DOIPubMedGoogle Scholar
  4. Wang  H, Li  Y, Liang  X, Liang  G. Japanese encephalitis in mainland China. Jpn J Infect Dis. 2009;62:3316.PubMedGoogle Scholar
  5. Wang  LH, Fu  SH, Wang  HY, Liang  GD, Cheng  JX, Jing  HM, Japanese encephalitis outbreak, Yuncheng, China, 2006. Emerg Infect Dis. 2007;13:11235.PubMedGoogle Scholar
  6. Solomon  T, Ni  H, Beasley  DW, Ekkelenkamp  M, Cardosa  MJ, Barrett  AD. Origin and evolution of Japanese encephalitis virus in southeast Asia. J Virol. 2003;77:30918. DOIPubMedGoogle Scholar
  7. Kuniholm  MH, Wolfe  ND, Huang  CY, Mpoudi-Ngole  E, Tamoufe  U, LeBreton  M, Seroprevalence and distribution of Flaviviridae, Togaviridae, and Bunyaviridae arboviral infections in rural Cameroonian adults. [Erratum in: Am J Trop Med Hyg. 2006;75:371]. Am J Trop Med Hyg. 2006;74:107883.PubMedGoogle Scholar
  8. Halstead  SB. Japanese encephalitis. In: Artenstein AW, editor. Vaccines: a biography. New York: Springer; 2010. p. 317–34.
  9. Cardosa  MJ, Hah  FL, Choo  BH, Padmanathan  S. Screening of pig sera for antibodies to Japanese encephalitis virus using a dot enzyme immunoassay and IgM capture ELISA: comparison with the hemagglutination inhibition and plaque reduction neutralization tests. Southeast Asian J Trop Med Public Health. 1993;24:4726.PubMedGoogle Scholar
  10. Erlanger  TE, Weiss  S, Keiser  J, Utzinger  J, Wiedenmayer  K. Past, present, and future of Japanese encephalitis. Emerg Infect Dis. 2009;15:17. DOIPubMedGoogle Scholar




Cite This Article

DOI: 10.3201/eid1705.101417

1These authors contributed equally to this article.

Related Links


Table of Contents – Volume 17, Number 5—May 2011

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:

Guo-Dong Liang, State Key Laboratory for Infectious Disease Prevention and Control, Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, 100 Yingxin St., Xuanwu District, Beijing 100052, People’s Republic of China

Send To

10000 character(s) remaining.


Page created: August 09, 2011
Page updated: August 09, 2011
Page reviewed: August 09, 2011
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.