[Analysis of genome determinants of virulence and setting-up of a library of full-size genome copies of the attenuated virus strain of the porcine reproductive and respiratory syndrome virus North American type].

Primary genome structures of 3 variants of the NADC-8 North American virulent strain of porcine reproductive and respiratory syndrome virus (PRRSV) were compared for the purpose of detecting any potential genetic virulence determinants of genus Arterivirus. Apart from the virulent variant, we also investigated the attenuated variant, obtained after 251 passages in cell culture, and the intermediate variant isolated from a pig after a partial reversion of the attenuated virus. The attenuated variant genome acquired a 3-nucleotide deletion and 50 mutations versus its virulent precursor.

Genomic characterization of virulent, attenuated, and revertant passages of a North American porcine reproductive and respiratory syndrome virus strain.

Pigs were exposed to three passages of the NADC-8 strain of porcine reproductive and respiratory syndrome virus (PRRSV) to investigate the relationship between genotypic and phenotypic properties. Differences were found in the virulence of the three passages called virulent, intermediate, and avirulent. Avirulent virus was derived by attenuation of virulent virus in cell culture and intermediate virus was derived by passage of avirulent virus in a pig.

Strain predominance following exposure of vaccinated and naive pregnant gilts to multiple strains of porcine reproductive and respiratory syndrome virus.

Two studies were performed in order to test the relative ability of different strains of porcine reproductive and respiratory syndrome virus (PRRSV) to replicate and cross the placental barrier in pregnant gilts. Study 1 comprised 6 nonvaccinated gilts. Study 2 comprised 8 nonvaccinated gilts and 12 gilts that were vaccinated twice before conception.

Comparative safety and efficacy of attenuated single-strain and multi-strain vaccines for porcine reproductive and respiratory syndrome.

The objective of this study was to compare the efficacy and safety of single-strain and multi-strain vaccines for the prevention of the respiratory facet of porcine reproductive and respiratory syndrome. The study comprised six groups of pigs (A through F, eight pigs per group). At the beginning of the study (Day 0) Groups C and D were vaccinated with a single-strain vaccine, and Groups E and F were vaccinated with a multi-strain vaccine.

Strain specificity of the immune response of pigs following vaccination with various strains of porcine reproductive and respiratory syndrome virus.

The primary objective of the study was to determine strain specificity of the immune response of pigs following vaccination with selected strains of porcine reproductive and respiratory syndrome virus (PRRSV). The experimental design included five groups (I through V, six pigs per group) free of antibody for PRRSV at the beginning of the experiment (day 0). On day 0, groups III, IV, and V were vaccinated with attenuated versions of PRRSV strains 8, 9, and 14, respectively.