| Porcine reproductive and respiratory syndrome(PRRS)is caused by infection of pigs with porcine reproductive and respiratory syndrome viruses(PRRSV),but PRRSV is constantly mutating,making it easy for PRRSV to evade the body’s immune response,resulting in a constant epidemic of PRRS.Nowadays,PRRS has become one of the major epidemics in large-scale pig farms in China,which greatly affects the healthy development of pig farming in China.In this study,we carried out the isolation and identification of PRRSV,and studied and analysed the epidemic situation of PRRS in China in 2021-2022,as well as the genetic change pattern of PRRSV,to provide a theoretical basis for the prevention and control of PRRS,as follows:1.Detection and sequencing analysis of PRRSV in clinical disease materialIn this study,a total of 2,691 clinical samples of porcine lymph nodes,lungs and aborted fetuses were collected from diseased pig farms in 24 provinces,municipalities and autonomous regions in China during 2021-2022.A total of 924 positive samples were detected by RT-PCR for ORF5 and Nsp2 genes,with a positive detection rate of 34.33%(924/2691).A total of 352 positive samples were randomly selected for sequencing analysis of the ORF5 gene.58.6%(171/352)were positive for Lineage 1(NADC30-like);19.0%(67/352)for Lineage 8(JXA1-like/CH-1a-like);19.0%(67/352)for Lineage 3(The positive detection rate for QYYZ-like was 9.4%(33/352);the positive detection rate for Lineage 5(VR2332-like)was 21.2%(77/352).Clinical samples from 1038 pig farms nationwide were tested,of which 472 farms were positive for PRRSV,with a positive detection rate of 45.47%(472/1038).Pig farms in different regions of China were tested and analysed: 85 pig farms in Northwest China(Xinjiang,Qinghai,Gansu,Ningxia,Shaanxi)were tested and 44 positive farms were found,with a detection rate of 76%(44/85).76%(44/85);256 pig farms in Southwest China(Tibet,Guizhou,Sichuan,Chongqing,Yunnan)were tested and 126 positive farms were found,accounting for 49.22%(126/ The number of positive pig farms tested in South China(Guangxi,Guangdong,Hainan)was 91 out of 179 farms,accounting for 50.84%(91/179);the number of positive pig holdings tested in East China(Jiangxi,Fujian,Zhejiang,Anhui,Jiangsu,Shandong)was 91 out of 213 holdings,accounting for 42.72%(91/213);the number of positive pig holdings tested in Central China(Henan,Hubei)163pig holdings were tested in Central China(Henan,Hubei,Hunan)and 66 positive pig holdings were found,accounting for 40.49%(66/163).2.Isolation and identification of PRRSV and sequencing and analysis of Nsp2 and ORF5 genesIn this study,61 samples identified as NADC30-like strains by RT-PCR were selected and inoculated onto PAM cells.10 PRRSV strains were isolated and a genetic evolutionary tree was constructed based on the ORF5 gene.8 strains were found to be on the sublineage 1.8(NADC30-like)branch and 2 strains were found to be on the The Nsp2 genetic tree was constructed and all 10 isolates belonged to sublineage 1.8.The strain from the Nsp2 region had 131 interrupted amino acid deletions(111+1+19)at loci322-432,483 and 504-522.3.Whole genome sequencing analysis of PRRSV isolatesWhole genome sequencing of 10 isolates was performed to obtain whole genome sequences of 5 PRRSV strains.Recombination analysis of the isolates with the reference strains(GM2,CH-1a,VR-2332,NADC30,JXA1)showed that all five isolates were recombinant strains,being recombinant strains of NADC30-like and JXA1,VR-2332 or NADC34-like.The recombination sites of these five isolates were mainly located in the Nsp2,Nsp9,GP5 and GP4 regions. |
