Isolation and characterization of a new subtype of Borna disease virus

Borna disease virus (BDV), the causative agent of severe meningoencephaliti s in a wide variety of animal species, has been considered to be geneticall y invariable and to form a single type within the genus Bornavirus of the f amily Bornaviridae, BDV infections are of particular interest, because for the first time a virus infection appears to be linked to human psychiatric disorders. We now describe a new subtype of BDV isolated from a horse which was euthanatized due to severe, incurable neurological disease. The nucleo tide sequence of this new strain, named No/98, differs from the reference s trains by more than 15%, and the subtype is difficult to detect by standard reverse transcriptase PCR protocols, The nucleotide exchanges of the novel BDV isolate have surprisingly little effect on the primary structures of m ost viral proteins, with the notable exception of the X protein (p10), whic h is only 81% identical to its counterpart in reference strains. Our data i ndicate that the genome of BDV is far more variable than previously assumed and that naturally occurring subtypes may escape detection by currently us ed diagnostic assays.