Isolation And Identification Of A Porcine Reproductive And Respiratory Syndrome Virus And Analysis Of Its Genomic Characteristics And Pathogenicity

Porcine reproductive and respiratory syndrome(PRRS)is a highly acute infectious disease caused by porcine reproductive and respiratory syndrome virus(PRRSV),which can infect pigs of all ages and has caused huge losses for the pig industry.PRRSV has been rampant in China for nearly 25 years since its emergence in 1995,especially in 2006 when the highly pathogenic porcine reproductive and respiratory syndrome virus(HP-PRRSV)emerged,dealing a severe blow to China's pig industry.Scientists have taken many measures to counter PRRSV,which has controlled the prevalence of PRRSV to a certain extent,but no effective measures have been found to completely eliminate it.From the perspective of viral genome,mutation and recombination are the core motility of PRRSV evolution.The rapid mutation of PRRSV strain has produced many strains with distant homology,which makes it difficult to achieve reasonable cross protection.In addition,the emergence of NADC30-like PRRSV in 2014,which is prone to recombination with other strains,further complicates the prevention and control of PRRSV.Based on the actual breeding practice,the tissue and blood of the infected pigs were collected from a pig farm in Shandong Province.And RT-PCR was performed to confirm that it was infected with PRRSV.After that,the virus was isolated and the virus isolation was verified by observing cytopathic effect(CPE)and indirect immunofluorescence(IFA).We then performed plaque purification and determined the whole genome of isolated virus SD-YL1712,and carried out genomic analysis including evolution analysis,amino acid deletion pattern analysis,nucleotide homology analysis,and recombinant analysis.The results showed that the isolated strain SD-YL1712 belongs to the recombinant strain formed by HP-PRSV JXA1-like and NADC30-like,and the recombination point is located in NSP2.It maintains the highest homology with JXA1-like strain,but its NSP2 region contains a discontinuous deletion of 131 amino acids specific for the NADC30-like strain.Finally,we used the JXA1 and CH1 a strains as controls to design an animal challenge experiment to investigate the pathogenicity of SD-YL1712 isolates on piglets.The results showed that it could cause severe hyperthermia,dyspnea,cough,loss of appetite and other clinical symptoms in piglets,and could cause piglets to be in the state of dying due to severe secondary infection.In addition,severe interstitial pneumonia was found in the lung tissue at autopsy.In conclusion,the SD-YL1712 isolate is similar to JXA1 strain and belongs to the highly pathogenic PRRSV isolate.In summary,this study successfully isolated a recombinant strain formed by JXA1-like and NADC30-like strains from the farm.The strain remains highly pathogenic to piglets and belongs to the highly pathogenic PRRSV isolation strain.This study provides a certain theoretical basis and data support for the detection of field PRRSV strain prevalence,the analysis of genome differences among epidemic strains,the exploration of the formation mechanism of recombinant strains and the genome characteristics and pathogenicity of recombinant strains.It provides a partial reference for the development of a newly efficient vaccine that can provide sufficient cross-protection effect for the heterogeneous PRRSV strains,especially for NADC30-like and recombinant strains.