Whole genome sequencing of clinical specimens reveals the genomic diversity of porcine reproductive and respiratory syndrome viruses emerging in China.

The Porcine reproductive and respiratory syndrome virus (PRRSV), a single (+) RNA virus, is characterized by high genome variability and constant evolution. Owing to increasingly complex mutations, there is a growing difficulty in accessing the whole genome. Additionally, there is limited knowledge on PRRSV intra-host nucleotide variants, which may reflect the complex viral-host dynamics. Here, we performed next-generation sequencing on four clinical lung tissues to reveal the genomic diversity and highlight virus-host interactions. The complete genomes of the HN0713 and GDYJ1224 strains shared 90.7% and 91.3% homology with the lineage 1 strain NADC30, respectively, while the GDGZ0408 and GDHY0425 strains shared 92.0% and 91.6% homology with the JXA1 strain, respectively. Recombination analysis showed that the ORF5-7 genes of the GDGZ0408 and GDHY0425 strains, whose complete genomes belong to lineage 8.7 based on the phylogenetic tree, are both recombined with lineage 3 strains. Furthermore, nsp3, nsp10-12, ORF2 genes and a part of the 3'-UTR of the GDHY0425 strain were provided by the lineage 5.1 strain. Two lineage 1 strains (GDYJ1224 and HN0713) were produced by a recombination of lineages 8.7 and 1. Additionally, the lineage 3 strain was associated with the recombinant HN0713 strain. We determined the intra-host single nucleotide variant frequencies and found more than 200 sites at a frequency of >1% in all samples. GDGZ0408 with parts of the nsp9 and nsp10 genes of HP-PRRSV lineage 8.7 presented more genetically diverse populations than others, indicating that lineage 8.7 might drive robust intra-host single nucleotide variants (iSNVs). Moreover, in the iSNV pools, nsp2 and ORF2a presented the highest mutation dynamic. Overall, this study provided evidence for the alarmingly increasing recombination and ever-changing evolutionary dynamics of PRRSV, and revealed the potential causes of vaccine escape, providing a novel insight into the nucleotide variant population in clinical samples.