Genetic clustering of Borna disease virus natural animal isolates, laboratory and vaccine strains strongly reflects their regional geographical origin

The aim of this study was to gain more detailed insights into the genetic evolution and variability of Borna disease virus (BDV). Phylogenetic analyses were performed on field viruses originating from naturally infected animals, the BDV vaccine strain 'Dessau', four widely used laboratory strains and the novel BDV subtype No/98. Four regions of the BDV genome were analysed: the complete p40, p10 and p24 genes and the 5'-untranslated region of the X/P transcript. BDV isolates from the same geographical area exhibited a clearly higher degree of identity to each other than to BDV isolates from other regions, independent of host species and year of isolation. Five different clusters could be established within endemic areas, corresponding to the geographical regions from which the viruses originated: (i) a Swiss, Austrian and Liechtenstein Rhine valley group, related closely to the geographically bordering Baden-Wurttemberg and Bavaria II group (ii) in the western part of Germany; (iii) a third group, called Bavaria I group, limited in occurrence to Bavaria; (iv) a southern Saxony-Anhalt and bordering northern Saxony group, bound to the territories of these federal states in the eastern part of Germany; and (v) a mixed group, consisting of samples from different areas of Germany; however, these were mainly from the federal states of Thuringia and Lower Saxony. The laboratory strains and the vaccine strain clustered within these groups according to their geographical origins. All field and laboratory strains, as well as the vaccine strain, clearly segregated from the recently described and highly divergent BDV strain No/98, which originated from an area in Austria where Borna disease is not endemic.