Construction And Application Of Chimeric Infentious Clones Of Porcine Reproductive And Respiratory Syndrome Virus

Porcine Reproductive and Respiratory Syndrome(PRRS) is a severe infectious disease. PRRS is a economically significant infectious disease in the swine industry worldwide. from 2006,"Porcine High Fever Syndrome" has spreaded all over the Chinese swine industry,the highly pathogenic(HP) PRRSV is one of the major cause pathogen.As the virus genome recombinating and mutating,the biological type,antigen type and genotype of PRRSV variated quickly,current control for PRRS is insufficient.The available vaccines are lack of antigencity and cross protection.It is urgent that more efficient PRRS vaccine should be developed.At the same time,the virulence factor of PRRSV is not known clearly. Based on our established PRRSV infectious clone of North American strain and first highly pathogenic(HP) PRRSV infectious clone in China,chimeric structural protein infectious clones are constructed successfully,in order to provide the platform for searching virulent factor and multi- valence PRRS vaccine.The detailed experimentations are discussed as follows.1.Construction of Chimeric Infectious Clones of PRRSVIn recent years,mass outbreaks of highly pathogenic(HP) porcine reproductive and respiratory syndrome virus(PRRSV) have spread all over the Chinese swine industry. There is no highly efficient PRRS vaccine to control it.Based on the first infectious cDNA clone of HP PRRSV strain pJX143 and that of an attenuated PRRSV,pAPRRS,we constructed several chimeric clones with various substitutions of structural protein genes (ORF4-7) and 3′UTR between attenuated pAPRRS and virulent pJX143.Upon transfection on Marc-145 cell lines,all chimeric constructs pSX12,p5NX12,and p56N12 were rescued. The rescued viruses maintain the similar virological properties,based on the results of the growth curve of the rescued viruses.In this study,three chimeric infectious clones are constructed successfully,the chimeric viruses can be passaged stably on Marc-145 cell.2.The Immunogenicity and Protection Study of Chimeric Virus vaccine CandidatesTo test if the chimeric viruses can be used as a vaccine candidate,the proper amount of vSX12 and v56N12 were used for vaccinated in pigs of 29 days old.As a result,the pigs vaccinated by vSX12 were all seroeonverted into positive 14-day-post vaccination,the neutralizing antibody of vSX12-vaccinated group increased from under 1:5 to 1:15 on 28th day,while v56N12 vaccinated pigs showed poor immuno responses.28 days post vaccination,the vSX12 group is challenged with the HP PRRSV JX143 strain,the vSX12-vaccinated group showed no signs of PRRS clinical symptom,and viremia period was shortened to 6 days.Our results demonstrated that 1) vSX12 chimeric virus is a good vaccine candidate;2) the virulence determinants of HP PRRSV probably located in coding regions other than ORF4-7 and 3′UTR,as our chimeric viruses were proved to be attenuated,this study could provide the significant platform for searching virulent determinants and developing multi- valence PRRS vaccine.