The strain was isolated in 1954 from the kidney of a yellow necked fildemouse (Apodemus flavicollis) in the Danube region of Czechoslovakia (Kmet, Ple{ko, 1956).
Factor analysis revealed its separate serological status (Kmety, 1977). The serovar name istrica was given, and it was suggested that it should be placed in the subgroup Sejroe of the Sejroe serogroup.