number of strains starting around 300 years ago. Different strains of the virus have been transmitted at least three times into Japan between 260–430 years ago. The strains circulating in Latvia appear to have originated from both Russia and Western Europe while those in Estonia appear to have originated in Russia. The Lithuanian strains appear to be related to those from Western Europe. Phylogenetic analysis indicates that the European and Siberian TBEV sub-types are closely related while the Far-eastern sub-type is closer to the Louping Ill Virus. However, in antigenic relatedness, based on the E, NS3, and NS5 proteins, all three sub-types are highly similar, and Louping Ill virus is the closest relative outside the collective TBEV group. History Though the first description of what may have been TBE appears in records in the 1700s in Scandinavia, identification of the TBEV virus occurred in the Soviet Union in the 1930s. The investigation began due to an outbreak of what was believed to be Japanese Encephalitis ("Summer encephalitis"), among Soviet troops stationed along the border with the Japanese empire (present day People's Republic of China), near the Far Eastern city of Khabarovsk. The expedition was led by virologist Lev A. Zilber, who assembled a team of twenty young scientists in a number of related fields such as acarology, microbiology, neurology, and epidemiology. The expedition arrived in Khabarovsk on May 15, 1937, and divided into squads, Northern-led by Elizabeth N. Levkovich and working in the Khabarovski Krai- and Southern-led by Alexandra D. Sheboldaeva, working in the Primorski Krai. Inside the month of May, the expedition had identified ticks as the likely vector, collected I. persucatus ticks by exposure of bare skin by entomologist Alexander V. Gutsevich and virologist Mikhail P. Chumakov had isolated the virus from ticks feeding on intentionally infected mice. During the summer, five expeditions members became infected with TBEV, and while there were no fatalities, three of the five suffered damaging sequelae. The expedition returned in mid-August and in October of 1937 Zilber and Sheboldova were arrested, falsely accused of spreading Japanese encephalitis. Expedition epidemiologist Tamara M. Safonov, was arrested the following January for protesting the charges against Zilber and Sheboldova. As a consequence of the arrests, one of the important initial works was published under the authorship of expedition acarologist, Vasily S. Mironov. Zilber was released in 1939 and managed to restore, along with Sheboldova, co-authorship on this