Epidemiological Detection Of PRRSV And PCV2 In Shandong Province And Pathogenicity Evaluation Of Co Infected And Sequential Infected In Post-weaned Pigs

Porcine reproductive and respiratory syndrome virus is the single stranded positive strand RNA virus in the genus Arterivirus of the family Arteriviridae.PRRSV can be divided into PRRSV-1 and PRRSV-2,PRRSV-2 is the dominant epidemic strain in China.PRRSV-2 can lead to reproductive failure,abortion,stillbirth and mummification and other clinical symptoms in sows;piglets and fattening pigs develop clinical signs,including dyspnea,increased body temperature,coarse disorganized dorsal hair,rash,and cyanosis in the ears.Porcine circoviruse is the single stranded negative circular DNA virus in the genus Circovirus of the family Circoviridae.PCVs is divided into PCV1-PCV4.PCV2 is the main etiological agent of porcine dermatitis nephropathy syndrome,which can be further divided into PCV2a-PCV2 g.PCV2d is the dominant strain in China,and it is mostly subclinical infection in the clinic and does not show obvious clinical symptoms.In this study,the molecular epidemiology of PRRSV and PCV2 in intensive livestock farm of Shandong Province were investigated,and used the China currently predominant NADC-30 like PRRSV strain and PCV2 d strain to infected PCV2 antibody negative post-weaned pigs and PCV2 antibody positive post-weaned pigs and conducted the pathogenicity by using mono infected,sequential infected,and co infected.The main results are as follows:(1)A total of 198 clinical samples were collected from intensive livestock farm in Shandong Province,and then PRRSV and PCV2 were detected after merged.For PCV2,the positive rates were 33.36%,and 19.12% for PRRSV;the rates of PCV2 and PRRSV co infection samples were 12.63%.The cap gene of PCV2 positive samples was sequenced;that the 7successfully sequenced PCV2 strains had the highest nucleotide and amino acid identity to the PCV2 d reference sequence,84.3-97.5% and 86.6-97.9%,respectively.The GP5 Gene of PRRSV positive samples was sequenced;all of the 13 PRRSV successfully sequenced strains were founded to belong to the NADC30-like PRRSV in lineage1.5,and four of these strains exhibited contiguous amino acid deletions at positions 33 and 44 and a mutation from lysine to arginine at position 151(characteristic of PRRSV virulent strains).(2)To determine the co infection characteristics of the NADC30-like PRRSV and PCV2 d,NADC30-like PRRSV and PCV2 d were used to infected the post-weaned pigs of PCV2 negative antibody,and established mono infected,sequential infected and co infected groups.It was found that sequential infected and coinfected showed more severe clinical symptoms,higher viral loads,and higher mortality,with 40% mortality in the sequential infected group and20% mortality in the co infected group;sequential infected of PRRSV and PCV2 can delays the production of PCV2 specific antibodies;co infected and sequential infected of PCV2 and PRRSV can lead the TNF-α,IFN-γ,IL-4 and IL-10 to elevated,and cytokine concentrations were higher in the co infected group and the PRRSV-PCV2 infected group.(3)At present,the immunization coverage of PCV2 vaccine in China is high,and most pigs are PCV2 antibody positive.There for the NADC30-like PRRSV and PCV2 d strains were used to infected the post-weaned pigs of PCV2 positive antibody,and established mono infected,sequential infected and co infected groups.The co infected group and sequential infected group showed more severe clinical symptoms and higher viral loads than the mono infected group,infected post weaned pigs of the PCV2 negative antibody,the viral load did show a significant decrease,after infected the post weaned pigs of the PCV2 positive antibody also showed varying degrees of decrease in viral load,Meanwhile,a significant decrease in mortality was also observed,only 20% mortality in the PCV2-PRRSV;coinfection or sequential infected of PCV2 and PRRSV in the presence of PCV2 antibodies can also lead the TNF-α,IFN-γ,IL-4 and IL-10 to elevated,and the PRRSV infected group exhibited a relatively high detection value of TNF-αand IL-10;the co infected group and sequential infected group exhibited more severe alveolar wall thickening and lymphocytic infiltration.In this study,the molecular epidemiology of intensive livestock farm in Shandong Province were investigated,and conducted the pathogenicity of currently major circulating NADC30- like PRRSV and PCV2 d on post weaned pigs in China,and lay the foundation for vaccine use and clinical prevention and control.