Pathogenicity Evaluation Of NADC30-like PRRSV And Development Its Infectious CDNA Clone

Porcine reproductive and respiratory syndrome is caused by porcine reproductive and respiratory syndrome virus(PRRSV).The main symptoms include severe reproductive failure,pneumonia,slow growth and the depression.Porcine reproductive and respiratory syndrome(PRRS),also known as blue ear disease,is one of the most prevalent pig diseases in the world.which was first reported in the United States in 1980 and caused huge economic losses in the pig industry.In 1992,the TW91 strain was found in Taiwan,China.In 1996,the classical strain CH-1a strain occurred in mainland China.In 2006,HP-PRRSV caused an extremely high mortality rate of pigs for many years seriously threatening China's pig industry.Obviously,an increasing incidence caused by NADC30-like PRRSV emerged in China since 2015.The most effective method for PRRS control is vaccine immunization.In spite of much research on PRRSV all over the world,the molecular characteristics and pathogenicity of the currently circulating NADC30-like strains need to be studied further.In this study,we first isolated and identified an unknown PRRSV strain from a Sichuan farm,and by RT-PCR,we demonstrated that this strain belongs to the class of NADC30 PRRSV.The isolated strain was named SC-d strain,and by the whole genome sequencing,we showed that there were 3 deletons(323-433 aa,483 aa and 504-522 aa)in the sequence of Nsp2 gene of SC-d strain,which had a total of 131 aa deletion.The recombinant analysis showed that the SC-d strain was a recombinant strain of the NADC30 strain and HP-PRRSV strain.At the same time,we further assessed its pathogenicity.The piglets inoculated with SC-d showed persistent fever,moderate weight loss,mild thymus atrophy,and pulmonary lesions.The pathogenicity of SC-d strain was lower than the highly pathogenic PRRSV HuN4 strain.Finally,we tried to construct an infectious clone of the SC-d strain by merging the full-length genome of the SC-d strain by RT-PCR.In conclusion,this study systematically analyzed the biological characteristics of NADC30 and attempted to construct infectious clones,which will provide theoretical basis and technical support for the prevention and control of NADC30 like strains in China.