Epidemiological Investigation Of PRRSV In China And Study On Attenuated Vaccine Of NADC30-Like PRRSV

Porcine Reproductive and Respiratory Syndrome(PRRS)is one of the most important disease that threats to world pig industry and causes great economic losses.Porcine Reproductive and Respiratory Syndrome virus(PRRSV)is the pathogen of PRRS,characterized by rapid evolution,containing PRRSV-1 and PRRSV-2.PRRSV-1 has four sub-genotypes,including subtype Ⅰ(Global;Clade A-L),subtype Ⅰ(Russian),subtype Ⅱ,subtype Ⅲ.PRRSV-2 has nine sub-genotypes,including lineage 1 to lineage 9.Currently,five sub-genotypes are prevalent in China,including subtype Ⅰ(Global:Clade A-L),lineage 1,lineage 3,lineage 5 and lineage 8.NADC30-like PRRSV of L1 branch with moderate or high pathogenic to piglets has become one of the dominant strains in China since 2016.Commercial vaccines of PRRSV development based on L5 and L8 branch could not provide complete protection for piglets against challenge of L1 branch PRRSV which seriously threaten the pig industry in China.To investigate the epidemic status of L1 branch PRRSV and its influence on pig industry in China,this study detected 2624 samples that suspected PRRSV infection from 22 Provinces,cities and autonomous regions.The results showed that the L1 branch was the main epidemic strain in China,followed by the L8 branch,and other types of PRRSV coexisted since 2016.Through genome-wide characterization analysis and biological characterization,we further determined its recombination patterns and pathogenicity to piglets of major endemic NADC30-like PRRSV and screened the parent strain(SD)used for vaccine development.Through passage in vitro,whole genome sequencing and animal test evaluation,a candidate live attenuated vaccine strain(SD-R)was obtained.The results demonstrated that SD-R strain had good safety and efficacy on piglets based on safety and efficacy evaluation.To evaluate the cross-protection effect of SD-R on other types of PRRSV,firstly,the study evaluate the cross-protection effect on heterologous NADC30-like PRRSV HLJWK108-1711 challenging piglets,and the results showed that SD-R could provide complete clinical protection to piglets after heterologous NADC30-like PRRSV challenge.Secondly,the study evaluated the cross-protection effect on NADC34-like PRRSV LNLNTZJ1341-2012 challenging piglets,and the results showed that SD-R could provide complete clinical protection to piglets after NADC34-like PRRSV challenge.Finally,the study evaluated the cross-protection effect on HP-PRRSV HuN4 challenging piglets,and the results showed that SD-R could provide clinical protection to piglets after HP-PRRSV challenge.In summary,this study determined that the L1 PRRSV has become the main epidemic strain in China.The NADC30-like wild strain SD was screened and attenuated,and the vaccine candidate SD-R strain had good safety and efficacy.SD-R could provide clinical protection to piglets whether homologous or heterologous NADC30-like PRRSV,NADC34-like PRRSV or HP-PRRSV challenged.