Epidemiology investigation of PRRSV discharged by faecal and genetic variation of ORF5

To obtain more information of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) transmission via faeces in/between farms, 360 swine faecal samples were randomly collected from different farms in China from 2017 to 2019. Sixty-two ORF5 genes were amplified by PCR from 120 positive samples identified by real-time RT-PCR and further characterized by sequencing. Phylogenetic analysis based on the ORF5 gene revealed that these strains can be divided into four lineages: lineage 1 (NADC30-like), lineage 3 (QYYZ-like), lineage 5.1 (VR2332-like) and lineage 8.7 (JXA1-like), with 62.9% (39/62) NADC30-like virus, 21% (13/62) QYYZ-like virus, 1.6% (1/62) VR2332-like virus and 14.5% (9/62) for JAX1-like virus. In particular, 14 PRRSVs including lineage 1, 5.1 and 8.7 can be isolated from 120 positive faecal samples, which further suggests that faecal transmission may be an important factor in the spread of PRRSV in farms. Full-length genome sequencing analysis showed that 14 isolates share 83.1%-97.7% homology with each other and 82.3%-96.1% identity with NADC30, 83.2%-99.7% with VR2332, 79.6%-87.2% with QYYZ and 82.6%-98.9% with JXA1 and CH-1a, and only 60.1%-60.7% with LV. Recombination events were observed in the six out of 14 strains. Collectively, the data of this study are useful for understanding the spread of PRRSV via faeces. Additionally, the virus was isolated from positive faecal samples, suggesting that faecal transmission may be an important factor in the spread of PRRSV in farms.