Abstract: The invention relates to the field of PRRS viruses and infectious clones obtained from PRRS viruses. Furthermore, the invention relates to vaccines and diagnostic assays obtainable by using and modifying such infectious clones of PRRS viruses. The invention provides a porcine reproductive and respiratory syndrom virus (PRRSV) replicon having at least some of its original PRRSV nucleic acid deleted, said replicon capable of in vivo RNA replication, said replicon further having been deprived of at least some of its original PRRSV nucleic acid and/or having been supplemented with nucleic acid derived from a heterologous microorganism.

Abstract: The invention provides antigenic sites of PRRSV isolates. The antigenic sites are neutralizing, conserved, non-conserved and conformational, can elicit antibodies and are found on protein GP4 and N encoded ORF4 and ORF7 of PRRSV. The peptide sequences identified by the sites can be incorporated in vaccines directed against PRRS and in diagnostic tests for PRRS. Also, discriminating tests can be developed that can be used next to marker vaccines in programs designed to eradicate PRRS from pig herds.