Etiological characterization of multiple recombinant lineages of TJ-C6 porcine reproductive and respiratory syndrome virus in Tianjin, Northern China.

Recent outbreaks of PRRSV in live attenuated vaccine-immunized pig farms in Tianjin, China have raised questions about the etiological characteristics and pathogenicity of the PRRSV variant, which remains unknown. In this study, a multiple lineages recombinant PRRSV strain named TJ-C6, was isolated and identified. Phylogenetic trees and genome homology analyses revealed that TJ-C6 belonged to lineage 1.8 (NADC30-like) and with similar 131 discontinuous amino acid deletion pattern (111-aa + 1-a + 19-aa) in Nsp2-coding region, but it was classified in lineage 1.5 (NADC34-like) cluster based on ORF5 sequence. Furthermore, the recombination analyses revealed that TJ-C6 was a multiple recombinant virus among lineage 1.5(NADC34- like), lineage 1.8(NADC30- like), and lineage 3(GM2-Like) strains with four recombination breakpoints in Nsp9 (nt 7298/8111), ORF2 (nt 12213) and ORF6 (nt 14628), which was different from the previously prevalent PRRSV strain. Challenge experiments with 3-week-old piglets showed that TJ-C6 could cause piglets high fever, loss of appetite and severely histopathological lung lesions. Taken altogether, multiple co-circulating lineages of PRRSV strains in the swine population are accelerating the emergence of natural recombinant strains with variations in pathogenicity and highlight the importance of surveillance of newly emerging PRRSV strains in China.