[Comparison of different BVD virus strains for their use in the differential diagnosis of classical swine fever--an attempt to standardize neutralization tests].

Six bovine virus diarrhoea (BVD) virus strains were tested in the neutralization test for their use in the differential diagnosis in classical swine fever (CSF) serology. The aim of the investigation was to find a suitable BVD virus strain guaranteeing a safe differentiation of CSF- and BVD virus induced antibodies using permanent cell cultures (PK-15, MDBK). For test purposes the neutralizing antibody titres of 73 defined test sera were titrated against the CSF virus strain Alfort/187 as well as the BVD virus strains Grub, Paplitz, NADL, 1138/69, Stendal, 10421/Han 94). Tests were repeated fivefold. The level of mean antibody titres, the differences in titre to the homologous pestivirus strain, the standard deviation and the variation coefficient served as test criteria. The BVD virus strains Grub and NADL yielded the best results. In view of harmonization and standardization the BVD virus strain NADL in connection with a standard protocol for neutralization tests is recommended for the differential diagnosis in CSF serology. Due to the adaptation of the permanent cell-lines PK-15 and MDBK to horse serum a further source of contamination with non cytopathogenic BVD viruses under routine conditions can be excluded.