Genetic Variation Analysis Of Porcine Reproductive And Respiratory Syndrome Virus In Henan Province

Porcine reproductive and respiratory syndrome(PRRS)is an acute,febrile and highly infectious disease characterized by reproductive and respiratory failure,caused mainly by an arteritis virus,porcine reproductive and respiratory syndrome virus(PRRSV).Although the virus is currently divided into two genotypes,its degree of genetic variation is constantly increasing with the continuous evolution of PRRSV,which brings great difficulties to the clinical prevention and control of the virus.Monitoring the genetic variation of the virus and the efficacy of its vaccines is a hotspot in related field.In this study,etiological and serological tests were performed on clinical samples from large-scale pig farms in Henan in2021,and sequencing analysis and virus isolation and culture of PRRSV on positive samples from 2018 to 2021.Our results are shown as below.The PCR method was carried out for etiological detection on 472 tissue and blood samples suspected of PRRSV infection.These samples were submitted by large-scale pig farms in Henan in 2021.43%(203/472)of the samples were found PRRSV positive.Analysis of the distribution of positive samples showed no obvious seasonal epidemic,but the infection rate was higher with greater fluctuation in temperature.Next,ELISA method was used to detect serological antibodies in 1630 whole blood samples submitted by largescale pig farms in Henan in 2021.The positive rate of PRRSV antibody was 76%(1231/1630).No seasonal differences were found in the distribution of the positive samples,consistant with previous results.Sequence analysis of NSP2 and ORF5 genes was performed on 200 PRRSV positive samples in Henan from 2018 to 2021.A total of 79 strains of NSP2 sequences were obtained in NSP2 sequencing analysis.They belong to two different subgroups.Discontinuous deletions of 1+29 amino acids were detected in 8 strains,which were consistent with the deletion characteristics of HP-PRRSV strain,with a 87.9%-99.9% nucleotide similarity;Discontinuous deletions of 111+1+19 amino acids were detected in 71 strains,characteristic of the NADC30 strain,with a 77.6%-97.8% similarity.These results show that the prevalent PRRSV strains in recent years in Henan are NADC30-like strains,and some strains have novel deletions with large variation.A total of 150 strains were obtained ORF5 sequencing analysis,belonging to 5 different subgroups.6,5,1,25,113 strains were closely related to VR2332,CH-1a,GM2,JXA1 and NADC30 with a 83.9%-99.7%,85.9%-98.5%,82.6%-90.4%,84.1%-99.3% and 85.4%-95.2% nucleotide similarity,respectively.These results indicate that the NADC30-like strain in Henan is gradually gaining grounds in recent years,becoming dominant strains.Furher analysis of important amino acid sites in the ORF5 sequence showed that the neutralizing epitopes and non-neutralizing epitopes,virulencerelated sites and glycosylation sites all mutated to varying degrees.non-neutralizing epitopes and glycosylation sites may lead to immune failure and increase the risk of PRRSV infection.9 strains were successfully isolated from 200 PRRSV positive samples in Henan from2018 to 2021,and further sequencing analysis of NSP2 and ORF5 protein found that 6 of them may have genetic recombination,Clinical prevention and control of the virus will be more difficult.In conclusion,multiple subtypes of PRRSV exist in the pig population in Henan province,but NADC30-like strain is the main strain.New variations have been detected in samples of recent years,mainly in the means of gene mutation,deletion and recombination.The PRRSV vaccine retains a good efficacy,but the infection of the pig polutation is in a hight rate possibly due to the significant variations in PRRSV.Our epidemiologic survey of the PRRSV provides valuable information to further work on this issue.