title: Reversion of a live porcine reproductive and respiratory syndrome virus vaccine investigated by parallel mutations.
abstract: A live attenuated porcine reproductive and respiratory syndrome (PRRS) vaccine virus has been shown to revert to virulence under field conditions. In order to identify genetic virulence determinants, ORF1 from the attenuated vaccine virus and three Danish vaccine-derived field isolates was sequenced and compared with the parental strain of the vaccine virus (VR2332). This revealed five mutations that had occurred independently in all three vaccine-derived field isolates, indicating strong parallel selective pressure on these positions in the vaccine virus when used in swine herds. Two of these parallel mutations were direct reversions to the parental VR2332 sequence and were situated in a papain-like cysteine protease domain and in the helicase domain. The remaining parallel mutations might be seen as second-site compensatory mutations for one or more of the mutations that accumulated in the vaccine virus sequence during cell-culture adaptation. Evaluation of the remaining mutations in the ORF1 sequence revealed stronger selective pressure for amino acid conservation during spread in pigs than during vaccine production. Furthermore, it was found that the selective pressure did not change during the time period studied. The implications of these findings for PRRS vaccine attenuation and reversion are discussed.
authors.affiliation: Danish Veterinary Institute for Virus Research, Lindholm, DK-4771 Kalvehave, Denmark1.
authors.forename: Henriette S
authors.initials: HS
authors.lastname: Nielsen
authors.affiliation: Danish Veterinary Institute for Virus Research, Lindholm, DK-4771 Kalvehave, Denmark1.
authors.forename: Martin B
authors.initials: MB
authors.lastname: Oleksiewicz
authors.affiliation: Institute of Biological Science, University of Aarhus, Aarhus, Denmark2.
authors.forename: Roald
authors.initials: R
authors.lastname: Forsberg
authors.affiliation: National Veterinary Research Institute, Pulawy, Poland3.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Stadejek
authors.affiliation: Danish Veterinary Institute for Virus Research, Lindholm, DK-4771 Kalvehave, Denmark1.
authors.forename: Anette
authors.initials: A
authors.lastname: Bøtner
authors.affiliation: Danish Veterinary Institute for Virus Research, Lindholm, DK-4771 Kalvehave, Denmark1.
authors.forename: Torben
authors.initials: T
authors.lastname: Storgaard
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics; D004252:DNA Mutational Analysis; D019143:Evolution, Molecular; D005814:Genes, Viral / Q000235:genetics; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010206:Papain / Q000737:chemistry; D010802:Phylogeny; D017354:Point Mutation / Q000235:genetics; D016133:Polymerase Chain Reaction; D019318:Porcine Reproductive and Respiratory Syndrome / Q000276:immunology / Q000821:virology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000201:enzymology / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity*; D017434:Protein Structure, Tertiary; D012641:Selection, Genetic; D013489:Suppression, Genetic / Q000235:genetics*; D013552:Swine; D014613:Vaccines, Attenuated / Q000009:adverse effects / Q000235:genetics* / Q000276:immunology; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics; D014765:Viral Vaccines / Q000009:adverse effects / Q000235:genetics* / Q000276:immunology; D014774:Virulence / Q000235:genetics
chemical_list: D014613:Vaccines, Attenuated; D014764:Viral Proteins; D014765:Viral Vaccines; D010206:Papain; D004265:DNA Helicases