Epidemiological survey and genomic characteristics of PRRSV in Hunan during 2021-2022

【Objective】 To investigate the epidemiological characteristics and genotype proportion of porcine reproductive and respiratory syndrome virus（PRRSV）in Hunan，which would provide reference for the prevention and control of PRRS in Hunan.【Method】 1184 tissue samples of pigs suspected of PRRSV infection were collected from 396 pig farms in Hunan from 2021，March to 2022，October，and the detected positive rates of different genotypes were determined by fluorescence quantitative PCR，and the PRRSV infection rates in different regions and seasons were counted. The ORF5 sequences of some positive samples were amplified by RT-PCR，and their sequence homology and genetic evolution were analyzed. Part of the disease samples were inoculated with Marc-145 cells for virus isolation. After the whole gene sequence was sequenced by second-generation sequencing technology，genetic evolution analysis was performed，and the occurrence of group recombination events was analyzed by SimPlot.【Result】167 tissue samples（detected positive rate 14.11%）were PRRSV-positive，the positive rate of PRRSV in different regions and seasons in Hunan were 0-46.43% and 6.95%-19.67% respectively. Moreover，the proportions of highly pathogenic PRRSV（HP-PRRSV），classical strains and NADC30-like strains were 43.11%，15.57%，and 41.32% respectively. Complete ORF5 gene sequences（600-603 bp）of 21 strains of PRRSV were amplified in this study，the homology analysis showed that 7 strains had the highest similarity （92.1%-98.9%）with the HP-PRRSV reference strains；13 strains showed the highest amino acid sequence similarity （91.3%-93.4%）with NADC30-like strains；only one strain were genetically identified with the PRRSV classical strains， with the sequence similarity of 98.6%-99.1%. The GP5 amino acid sequence of different PRRSV was highly variable，and two NADC30-like strains had deletion of amino acid sites in the GP5 amino acid sequence highly variable region，and the amino acid variation regions of some PRRSV strains were mainly located in the GP5 cell epitope region. Two PRRSV strains（named HuN-A and HuN-B）were isolated. HuN-A strain belonged to the NADC30-like strain，with NADC30 strain as the main parent and HP-PRRSV strain as the secondary parent. However，the HuN-B strain belonged to HPPRRSV strain.【Conclusion】The prevalence of PRRSV in Hunan was serious and there are many genotypes，among which NADC30 strains and HP-PRRSV strains are the main genotypes. Two PRRSV strains are successfully isolated，the HuN-A strain is recombinant from the NADC30-like strain and the HP-PRRSV like strain（JXA1），while HuN-B strain may be produced by the atavism of JXA1 attenuated vaccine strain.