| Porcine reproductive and respiratory syndrome(PRRS)caused by porcine reproductive and respiratory syndrome virus(PRRSV)is a viral disease impacting severely the pork industry.In recent years,the prevalence of PRRSV NADC30-like that bring a huge challenge to control of PRRS have been described by the researchers in China This present study aimed to mornitor the infection of NADC30-like strains and to investigate genomic characteristics and pathogenicity of PRRSV isolate in Tianjin region in order to provide evidence for the prevention and control of PRRSV NADC30-like infection in China.The RT-PCR method that simultaneously distinguishes the classical,highly pathogenic(HP)and NADC30-like PRRSV was established based on Nsp2 gene.396 clinical samples collected from 63 farms during 2014-2016 were detected.The results showed that the positive rate for PRRSV was 26.26%(104/396),and 69.23%(72/104),4.81%(5/104),25.96%(27/104)for HP-PRRSV,classical PRRSV,NADC30-like PRRSV,respectively.The posititive rate for NADC30-like PRRSV was 6.25%;17.07%,58.06%during 2014 to 2016 that showed an increasing tendency.The phylogenetic analysis based on Nsp2 gene revealed that 13 strains of PRRSV NADC30-like contained a discontinuous deletion of 131 amino acids and additional 2 amino acids in the Nsp2-coding region.The phylogenetic analysis based on ORF5 gene indicated that 3 strains of PRRSV NADC30-like had 1 amino acids deletion in the GP5-coding region,causing the diversity of NADC30-like strains.With the investigation of PRRSV vaccine vaccination,all the swine farms practicing vaccination with classical PRRSV vaccines(MLV-VR2332,CH-1R and R98)and HP-PRRSV-derived vaccines(TJm-F92 and JXA1-R)were infected by PRRSV NADC30-like.Seven stains of PRRSV which were named TJnh1401,TJnh1501,TJnh1502,TJdg1601,TJdg1602,TJbd1601 and TJbd1602 were isolated by using MARC-145 cells,and identified by RT-PCR and IFA.Based on the genetic analysis of Nsp2 and ORF5,TJnh1501 was purified and its whole genome was sequenced and analyzed.The results showed that the virus titer of TJnh1501 on MARC-145 cells was up to 107.0TCID50,and the homology of the whole genome sequence with the PRRSV NADC30 was only 86.6%,and the homology with HP-PRRSV was as high as 96.3%,while it’s Nsp2 has the molecular characteristics of 131 amino acid deletion similar to the NADC30.The results of SimPlot biology software showed that TJnh1501 was a recombinant virus between HP-PRRSV-derived vaccine and NADC30,and the recombination site was located at the 1737 nt-3506 nt in the nonstructural protein-coding region(Nsp2).The pathogenicity of the recombinant virus TJnh1501 for piglets was analyzed.The results showed that the clinical symptoms of the inoculated piglets included fever,depression,dyspnea,and decreased ADG following TJnh1501 infection.The lungs of the infected piglets exhibited edema,pulmonary consolidation,peripheral bronchial inflammatory cell infiltration,bronchial mucosal epithelial shedding and intravascular bleeding,the lung score of TJnh 1501-infection group was significantly higher than that of control group(p<0.05).The results showed that the recombinant virus TJnh 1501 had pathogenicity for piglets.The protective efficiency of the commercial PRRSV vaccines against TJnh1501 was further evaluated.Vaccination with MLV Inglevac PRRS(?)and HP-PRRSV(JXA1-R)failed to provide protective efficiency from TJnh1501 challenge in piglets,showing that these two kinds of vaccines induced on cross-protection efficacy against TJnh1501 infection. |
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