Isolation, Identification and Genetic Evolution Analysis of a Multilineage Recombinant Porcine Reproductive and Respiratory Syndrome Virus

Purpose To investigate the genetic evolution of porcine reproductive and respiratory syndrome virus (PRRSV).

Methods Blood samples from diseased pigs and lung tissues from dead pigs were collected from a suspected porcine reproductive and respiratory syndrome outbreak pig farm in Anhui Province. RT-PCR, indirect immunofluorescence assay, virus growth curve and bioinformatics software were used for virus isolation, identification and gene sequence analysis.

Results A strain of PRRSV was isolated from Marc-145 cells and designated as AH1. The complete genome of AH1 was 15022 bp in length, which shared 90.0% nucleotide identity with the NADC30 strain from USA. The virus titer was 10^5.67 mL⁻¹. Phylogenetic analysis based on the whole genome showed that AH1 and NADC30-like strain were on the same branch of the genetic evolutionary tree, and had characteristic insertion or deletion of amino acids in NSP2 region similar to NADC30-like strain. The tenth amino acid of GP2 protein was mutated from L10 to S10. Recombinant analysis showed that PRRSV AH1 was a recombinant strain with NADC30 as the backbone and PRRSV CH-1a, JXA1 and QYYZ strains providing recombinant fragments.

Conclusion Strain AH1 results from multiple recombinations among PRRSV lineage 1, lineage 3 and lineage 8, and new virulence-associated amino acid mutations occur at the same time. This study provides a new reference for the study of the epidemic distribution and genetic variation of PRRSV recombinant strains in China.