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

Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.

Volume 32, Number 12—December 2026

Dispatch

Wild Mice and Shrews as Natural Reservoirs of Emerging Tickborne Yezo Virus, Hokkaido, Japan, 2023–2025

Mebuki Ito, Yuma Ohari, Isshu Kojima1, Yume Mimura, Keita Mizuma2, Jingshu Li, Hayato Torisu, Shumpei Kamiyama, Tomoki Sakiyama3, Hironori Mieda, Naoya Matsumoto, Natsumi Iijima, Eri Fujii, Yasuko Orba, Kuniko Kawai, Satoshi D. Ohdachi, and Keita MatsunoComments to Author 
Author affiliation: Hokkaido University International Institute for Zoonosis Control, Sapporo, Japan (M. Ito, Y. Ohari, I. Kojima, Y. Mimura, K. Mizuma, J. Li, E. Fujii, Y. Orba, K. Matsuno); Hokkaido University Graduate School of Environmental Science, Sapporo (H. Torisu, T. Sakiyama, H. Mieda); Tokai University Graduate School of Biology, Sapporo (S. Kamiyama, K. Kawai); Sapporo Maruyama Zoo, Sapporo (N. Matsumoto, N. Iijima); Hokkaido University Institute of Low Temperature Science, Sapporo (S.D. Ohdachi)

Main Article

Figure 1

RNA copy numbers and viral titers in organs of wild small mammals in study of wild mice and shrews as natural reservoirs of emerging tickborne Yezo virus, Hokkaido, Japan, 2023–2025. A) Copy numbers of 3 segments in the livers of wild small mammals. Liver samples positive for the S segment were used for this analysis. The detection limits were 1.62 log10 copies/mg for M segment and 1.52 log10 copies/mg for L segment. B–E) RNA copy numbers and viral titers of the serum and internal organs quantified using the 2 animals from which the virus was isolated (HAs25-107 and HSg23-013). B, C) Copy numbers of the S segment RNA quantified by quantitative reverse-transcription PCR. D, E) TCID50 determined using ISE6 cells (Ixodes scapularis embryo–derived cells), which was provided by the Centre for Ecology and Hydrology Institute of Virology and Environmental Microbiology (Oxford, UK) (14). The detection limits of virus titer were −0.5 log10 TCID50/mg for the liver, lung, and heart of HSg23-013; −2.5 log10 TCID50/μL for serum of HAs25-107; and −1.5 log10 TCID50/mg for the other samples. Serum, kidney, and brain samples of HSg23-013 were not available. L, large; M, medium; ND, not detected; S, small; TCID50, 50% tissue culture infectious dose.

Figure 1. RNA copy numbers and viral titers in organs of wild small mammals in study of wild mice and shrews as natural reservoirs of emerging tickborne Yezo virus, Hokkaido, Japan, 2023–2025. A) Copy numbers of 3 segments in the livers of wild small mammals. Liver samples positive for the S segment were used for this analysis. The detection limits were 1.62 log10 copies/mg for M segment and 1.52 log10 copies/mg for L segment. B–E) RNA copy numbers and viral titers of the serum and internal organs quantified using the 2 animals from which the virus was isolated (HAs25-107 and HSg23-013). B, C) Copy numbers of the S segment RNA quantified by quantitative reverse-transcription PCR. D, E) TCID50 determined using ISE6 cells (Ixodes scapularis embryo–derived cells), which was provided by the Centre for Ecology and Hydrology Institute of Virology and Environmental Microbiology (Oxford, UK) (14). The detection limits of virus titer were −0.5 log10 TCID50/mg for the liver, lung, and heart of HSg23-013; −2.5 log10 TCID50/μL for serum of HAs25-107; and −1.5 log10 TCID50/mg for the other samples. Serum, kidney, and brain samples of HSg23-013 were not available. L, large; M, medium; ND, not detected; S, small; TCID50, 50% tissue culture infectious dose.

Main Article

References
  1. Kodama  F, Yamaguchi  H, Park  E, Tatemoto  K, Sashika  M, Nakao  R, et al. A novel nairovirus associated with acute febrile illness in Hokkaido, Japan. Nat Commun. 2021;12:5539. DOIPubMedGoogle Scholar
  2. Zhang  MZ, Bian  C, Ye  RZ, Cui  XM, Yao  NN, Yang  JH, et al. A series of patients infected with the emerging tick-borne Yezo virus in China: an active surveillance and genomic analysis. Lancet Infect Dis. 2025;25:390–8. DOIPubMedGoogle Scholar
  3. Ogata  Y, Sato  T, Kato  K, Kikuchi  K, Mitsuhashi  K, Watari  K, et al. A case of tick-borne Yezo virus infection: concurrent detection in the patient and tick. Int J Infect Dis. 2024;143:107038. DOIPubMedGoogle Scholar
  4. Yamaguchi  H, Mizuma  K, Watari  K, Ohari  Y, Mitsuhashi  K, Tamiya  K, et al. Epidemiological, clinical, and virological characterizations of Yezo virus infections, an emerging tick-borne orthonairovirus disease in Japan. J Infect Dis. 2026;233:1036–45. DOIPubMedGoogle Scholar
  5. Epik  YO, Sycheva  KA, Karan  LS, Mokretsova  EV, Dragomeretskaya  AG, Trotsenko  OE, et al. Yezo virus diversity in tick bite patients and ticks, Russia. Emerg Infect Dis. 2026;32:759–62. DOIPubMedGoogle Scholar
  6. Ito  M, Minamikawa  M, Kovba  A, Numata  H, Itoh  T, Katada  Y, et al. Environmental and host factors underlying tick infestation in invasive raccoons (Procyon lotor) in Hokkaido, Japan. Ticks Tick Borne Dis. 2024;15:102389. DOIPubMedGoogle Scholar
  7. Ito  M, Minamikawa  M, Kovba  A, Numata  H, Itoh  T, Ariizumi  T, et al. Environmental and host factors underlying tick-borne virus infection in wild animals: investigation of the emerging Yezo virus in Hokkaido, Japan. Ticks Tick Borne Dis. 2024;15:102419. DOIPubMedGoogle Scholar
  8. Ito  M, Ohari  Y, Kishimoto  M, Matsuno  K. Spatial distribution of ticks and tick-borne pathogens in central Hokkaido, Japan and associated ecological factors revealed by intensive short-term survey in 2024. PLoS One. 2026;21:e0349386. DOIPubMedGoogle Scholar
  9. Nishino  A, Tatemoto  K, Ishijima  K, Inoue  Y, Park  ES, Yamamoto  T, et al. Transboundary movement of Yezo virus via ticks on migratory birds, Japan, 2020–2021. Emerg Infect Dis. 2024;30:2674–8. DOIPubMedGoogle Scholar
  10. Yamaguti  N, Tipton  V, Keegan  H, Toshioka  S. Ticks of Japan, Korea, and the Ryukyu Islands. Brigham Young University Science Bulletin. Biological Series. 1971;15:1.
  11. Ohdachi  DS, Ishibashi  Y, Iwasa  AM, Fukui  D, Saitoh  T. The wild mammals of Japan, 2nd edition. Kyoto: Shoukadoh Book Sellers; 2015.
  12. The American Society of Mammalogists. The mammal diversity database [cited 2026 Jan 14]. https://www.mammaldiversity.org/index.html
  13. Ohdachi  S. Home ranges of sympatric soricine shrews in Hokkaido, Japan. Acta Theriol (Warsz). 1992;37:91–101. DOIGoogle Scholar
  14. Munderloh  UG, Kurtti  TJ. Formulation of medium for tick cell culture. Exp Appl Acarol. 1989;7:219–29. DOIPubMedGoogle Scholar
  15. Apanasevich  M, Dubovitskiy  N, Derko  A, Khozyainova  A, Tarasov  A, Kokhanenko  A, et al. Genomic characterization of a novel Yezo virus revealed in Ixodes pavlovskyi tick virome in western Siberia. Viruses. 2025;17:1362. DOIPubMedGoogle Scholar

Main Article

1Current affiliation: Okayama University of Science Faculty of Veterinary Medicine, Imabari, Japan.

2Current affiliation: Tokyo University, Tokyo, Japan.

3Current affiliation: Umeå University, Umeå, Sweden.

Page created: September 05, 2026
Page updated: October 27, 2026
Page reviewed: October 27, 2026
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.
file_external