Porcine pestivirus designated herein as atypical porcine pestivirus (“APPV”) (Genbank accession no. KR011347.1). Immunogenic compositions to induce an immune response against porcine pestivirus infection in a pig are described, which APPV antigenic agents (e.g., isolated whole virus, derivatives thereof, functional fragments thereof, and combinations of the foregoing). Methods of vaccinating against porcine pestivirus infection using the immunogenic compositions are also described. The methods can be also applied for clinical research and/or study, including diagnostic methods for detecting pestivirus infection using monoclonal antibodies specifically binding to APPV epitopes.