The Isolation,identification And Genetic Evolution Analysis Of PVC2 Virus In A Large-scale Hoggery Of Guangdong Province And Evaluation Of The Use Of Circovirus Vaccine

Porcine circovirus-2(PCV-2)is a circular,non-enveloped single-stranded DNA virus.Up to now,it is one of the major causes of weaning piglet multisystem wasting syndrome(PMWS),which is the smallest animal pathogenic virus.The disease was first discovered in Canada in 1991 after then it became a global epidemic rapidly,China reported the disease in 2000 for the first time.In order to investigate the epidemic situation of PCV2 in large-scale pig farms,we collected the visceral and lymph node grinding materials of suspected sick pigs from 2014 to 2016,we detected the pathogen with PCV2 detection primers,and then detected the isolation and identification of pathogen virus on PK-15 cells.There were eight strains of virus named GD-2,GD-3,GD-4,GD-5,GD-6,GD-7 and GD-8 were isolated and identification.The genetic and phylogenetic tree showed that GD-1,GD2,GD-3,GD-4,GD-5,GD-7 and GD-8 belonged to PCV2 b genotype,while GD-6 belonged to PCV2 a genotype.PCV2 virus usually has 1767 bp and 1768 bp full-length.Eight isolates of this virus isolate 1768 bp of GD-6 and 1767 bp of the seven strains.In addition,10 strains of PCV2 virus at home and abroad were used as the reference strain and the 8 strains of PCV2 viruses were used to analyze their genotyped,ORF1 and ORF2 amino acid homology,The results showed that the whole genome homology of the virus isolated in this study was higher than that of the reference strain at home and abroad at more than 93%,the other ORF1 of the virus was highly conserved,and the ORF2 homology of the virus showed a low homology of 87.4%-88.5% with the PCV2 c genotype.In addition,the isolates and reference strains at home and abroad do not have the regional homology differences,indicating that the PCV2 epidemic strains of genotypes in the world have a wide range of identification with others.The Rep protein of PCV2 has three glycosylation sites: 23-25aa(NPS),256-258aa(NQT)and 286-288aa(N AT),according to the Rep protein encoded by ORF1 and the Cap protein amino acid site encoded by ORF2.The three glycosylation sites were highly conserved and changed.In addition,the result showed that the Cap protein was the key protein of the virus and had no amino acid mutation at its glycosylation site 143-145aa(NYS).The Cap protein had three hyper variable regions located in the amino acid sequence.According to the PCV2 b genotype,the genotype of the strain 86-89 has a specific amino acid position to identify SNPR(L),and PCV2 a genotype strain has specific recognition motif TNKI,it was deduced that GD-6 belonged to PCV2 a,and the other seven isolates belonged to the genotype of PCV2 b.the results were consiste nt with the entire genetic evolution analysis.In this study,we investigated the prevalence of PCV2 and the specificity of PCV2,which can provide the reference for the preve ntion and control of PCV2.Vaccine immunization is an effective method for the preve ntion and control of PCV2.This study is designed to evaluate the immune effects of differe nt PCV2 vaccines.We selected 120 suckling piglets randomly,and divided them into three groups.We imported immune vaccine,domestic round-ring virus vaccine and saline,as well as observed the feed conversation rate,daily gain,morbidity and other indexes of the vaccinated group during the nursery stage.The results showed that the ratio of feed conservation rate of imported PCV2 vaccine group and home-bred PCV2 vaccine group decreased by 0.32 and 0.13 respectively,and the daily gain increased by 60 g and 12 g respectively,which indicated that the PCV2 vaccine of the PCV can decrease the daily gain of pigs and raise the feed-meat ratio during the nursery stage.The clinical use of PCV2 vaccine can achieve good economic benefits.