Characterization of tick-borne encephalitis virus isolated from tick infesting dog in central Hokkaido in 2018

Tick-borne encephalitis virus (TBEV) is a zoonotic virus belonging to the genus Flavivirus of the family Flaviviridae, causing meningitis or meningoencephalitis in humans. TBEV is widely distributed across the Eurasian northern regions, including Japan. Dogs have been reported to be sentinel hosts of TBEV in endemic areas, but studies of ticks infesting dogs are limited in Japan. This study isolated a novel TBEV strain from a tick (Ixodes ovatus) collected on a dog from central Hokkaido. Whole-genome sequencing revealed that the isolated strain belonged to the Far Eastern subtype of TBEV and was classified under a different subcluster of other Japanese isolates. Nanporo-18-44 showed growth properties similar to those of Oshima 5-10 both in vitro and in vivo. The pathogenicity of both viruses was similar in mice infected intracerebrally, however they showed a distinct distribution in the infected neurons of the mouse brain. Our results suggest that infections of humans and animals by unknown strains of TBEV exist in other areas of Japan. Further surveys including those conducted outside of Hokkaido, are required to elucidate the epidemiological risk of TBEV in Japan.