Shishan Yuan

Recombination between North American strains of porcine reproductive and respiratory syndrome virus

Abstract Porcine reproductive and respiratory syndrome virus (PRRSV), a recently discovered arterivirus swine pathogen, was shown to undergo homologous recombination. Co-infection of MA-104 cells with two culture-adapted North American PRRSV strains resulted in recombinant viral particles containing chimeric ORF 3 and ORF 4 proteins. Nucleotide sequence analysis of cloned recombinant PCR products, encompassing 1182 bases of the 15.4 kb viral genome, revealed six independent recombination events. Recombinant products persisted in culture for at least three passages, indicating continuous formation of recombinant viruses, growth of recombinant viruses in competition with parental viruses, or both. The frequency of recombination was estimated from <2% up to 10% in the 1182 b fragment analyzed, which is similar to recombination frequencies observed in coronaviruses. An apparent example of natural ORF 5 recombination between naturally occurring wild type viruses was also found, indicating that recombination is likely an important genetic mechanism contributing to PRRSV evolution.

Complete genome comparison of porcine reproductive and respiratory syndrome virus parental and attenuated strains

Abstract Two full-length porcine reproductive and respiratory syndrome virus (PRRSV) genomes, strain VR-2332 and its cell culture passaged descendent RespPRRS vaccine strain, were compared and analyzed in order to identify possible sites of attenuation. Of the 44 nucleotide changes, 13 resulted in conservative changes and 18 produced non-conservative changes. The results suggest that key amino acids in ORF1 may contribute to the phenotype of RespPRRS, which includes increased growth rate on MA-104 cells and decreased virulence in swine. The results provide a genetic basis for future manipulation of a PRRSV reverse genetics system.

Appearance of Novel PRRSV Isolates by Recombination in the Natural Environment

Porcine reproductive and respiratory syndrome virus (PRRSV) emerged in North America and Europe in the 1980’s as a new viral disease of swine. PRRSV now is endemic in swine-rearing regions essentially worldwide. A better understanding of the mechanisms of genetic change may help to elucidate its evolutionary history and emergence as a swine pathogen.

Predicted RNA Folding Suggests PRRSV Major and Heteroclite Subgenomic Transcripts Result from Polymerase Switching at Unpaired Nucleotides

Porcine reproductive and respiratory syndrome virus (PRRSV) has emerged as a major disease of swine worldwide, causing stillbirths and abortions in pregnant sows and reproductive failure in young swine. Even though modified-live vaccines have been used for many years, PRRSV continues to thrive and spread. Previous work has shown that one of the mechanisms which PRRSV uses to evade host defenses is to undergo viral recombination at a high frequency (Yuan et al 1999). The high frequency nidovirus recombination mechanism occurs by discontinuous transcription (Baric et al 1987) that appears to be guided by basepairing between sense and antisense strands at sites of secondary structure. Support for this model has been recently been obtained for equine arteritis virus subgenomic (sg) mRNAs, which utilize a common leader body junction site sequence which undergoes sequential basepairing at two distinct sites on the genome of the opposite strand (Marle et al 1999). In this report, we document that besides standard PRRSV sg mRNAs, other subgenomic RNAs, which utilize alternative junction sites, are transcribed during PRRSV infection. We also provide evidence that these novel subgenomic RNAs are produced by a similar basepairing mechanism, yet the newly identified RNAs appear to be generated in a less-stringent manner. Thus, the PRRSV polymerase complex appears to be more promiscuous than other nidoviruses complexes in deciding where and when to switch templates during transcription. The identification of these novel subgenomic RNAs during normal PRRSV infection will allow further characterization of the specific mechanism for nidovirus discontinuous transcription.

Packaged Heteroclite Subgenomic RNAs of PRRSV

Porcine reproductive and respiratory syndrome virus (PRRSV) is a member of the Arteriviridae family of the Nidovirales (Meulenberg et al, 1993b; Nelsen et al., 1999). While the complete genomes of three PRRSV strains are known (Allende et al., 1999; Meulenberg et al., 1993; Nelsen et al., 1999), main questions remains to be elucidated concerning viral replication and transcription processes.

Erratum to “Complete genome comparison of porcine reproductive and respiratory syndrome virus parental and attenuated strains”: [Virus Research 74 (2001) 99–110]

Two full-length porcine reproductive and respiratory syndrome virus (PRRSV) genomes, strain VR-2332 and its cell culture passaged descendent RespPRRS vaccine strain, were compared and analyzed in order to identify possible sites of attenuation. Of the 41 nucleotide changes, 12 resulted in conservative changes and 18 produced non-conservative changes. The results suggest that key amino acids in ORF1 may contribute to the phenotype of RespPRRS, which includes increased growth rate on MA-104 cells and decreased virulence in swine. The results provide a genetic basis for future manipulation of a PRRSV reverse genetics system.