Six antigenic groups within the genus pestivirus as identified by cross neutralization assays.

Antigenic differences between pestivirus isolates of ruminant and porcine origin were characterized by neutralization assays. First, six different clusters of pestiviruses were identified by clustering cross-neutralization results of 13 pestivirus strains tested against 23 sera. Cluster I consisted of four strains of bovine viral diarrhoea virus (BVDV) of bovine origin and two BVDV isolates of porcine origin. Cluster II consisted of one sheep isolate and two porcine BDV isolates. Cluster III consisted of one classical swine fever virus strain and cluster IV, V, and VI each consisted of one strain isolated from a giraffe, a deer, and a pig. After the clusters were identified, one-way neutralization tests were used to test a total of 45 pestivirus isolates. Although the same six groups were found, results of some individual strains differed from previous cross-neutralization results and the results obtained by typing with monoclonal antibodies. The discrepancy between one way neutralization tests and cross-neutralisation tests is demonstrated clearly by recalculation of the cross-neutralization results without the classical swine fever sera. We conclude that neutralization tests are only suitable to characterize antigenic differences when virus strains are tested in a cross-neutralization test.