In vitro studies on Borna virus. II. Properties of the virus.

Successful cultivation and titration of Borna disease virus in cell cultures enabled detailed studies of the virus properties. Borna virus is labile towards treatment with heat, pH 3.0 and lipid solvents. It is relatively stable at low temperatures and in frozen state. It is easily inactivated by ultraviolet light as e.g. vesicular stomatitis virus. After ultrafiltration studies, the size of the infectious virus unit is between 80 and 100 nm. Its buoyant density in cesium chloride is 1.165 g per ml. The one step multiplication curve shows that Borna virus has a replication cycle of about 2 days in BSC 1 cells. In growth experiments using antimetabilites it behaves like certain RNA containing viruses. As its multiplication is not inhibited by bromo- and iododeoxyuridine and actinomycin D, no DNA step seems to be involved in virus synthesis. Regarding these properties and the intracellular antigen distribution as shown by fluorescent antibodies, it is not possible to attribute Borna virus to any of the established virus groups.