Genetic Variation Of NSP2of PRRSV Isolates In China And Evaluation On The Safety Of PRRS Live Vaccine

Porcine reproductive and respiratory syndrome (PRRS) is a most important infectious diseasecaused by PRRS virus (PRRSV)，which has been characterized by reproductive failure during lateterm gestation in sows and respiratory tract distress in piglets. It can cause enormous economiclosses in the swine industry all over the world. The PRRSV was divided into classic PRRSV andhighly pathogenic PRRSV (HP-PRRSV) based on its pathogenicity and genomic molecularcharacteristics. The HP-PRRSV had been epidemic in South of China in2007, and the1+29amino acid (aa) deletion in nonstructural protein2(NSP2) is the important molecular features ofHP-PRRSV that distinguish from the classic PRRSV strain. To clarify epidemic strains origin andvariation characteristics, and the safety of the PRRS live vaccine, the PRRSV strains were isolatedfrom the swine suspected PRRSV infection in different time and regions, and NSP2geneticevolution characteristics of PRRSV isolates was analyzed. PRRS live vaccine safety wasevaluated, and the PRRS live vaccine application effect was investigated in this study.1300samples were collected from pigs suspected PRRSV infection in12provinces in2005～2010, the PRRSV were isolated by alveolar macrophages and Marc-145cells. The isolatesstrain were identified by RT-PCR and IFA, and virion with the diameter of about45-65nm wasshowed by electronic microscopy. Eventually,39strains of PRRSV were isolated in this research.After the Nsp2genes of the isolates were cloned and analyzed, we found that35isolates contained1aa+29aa deletion in NSP2(type H), and3isolates contained1aa+4aa+29aa deletion in NSP2(type Z), and1strains contained1aa deletion in NSP2(type G). There are3types of NSP2deletion virus, and others3isolates contained30aa+29aa deletion in NSP2(type W). Accordingto the NSP2variation, including CH-1a as representatives of type C, the PRRSV strains can bedivided into5type isolates (C, G, H, Z and W type).The safety of the commercial classic and highly pathogenic PRRS live vaccine was evaluatedby the animal experiment. Two PRRS live vaccine were inoculated nursery pig and late pregnantsows by single repeated dose or high dose test. The results showed that the classical PRRS vaccineon sows and piglets is safe, the pigs inoculated with classic PRRS live vaccine have shorterviremia and shedding time, and the piglets from vaccinated sows were not infected by classicPRRSV strain. While the pigs inoculated with highly pathogenic PRRS vaccine have a longviremia and shedding time (more than4weeks), highly pathogenic PRRS vaccine can result invaccinated pregnant sows reproductive failure, and the most piglets from vaccinated sows wereinfected by highly pathogenic PRRSV strain.A total of355farms were investigated about the application effect of PRRS live vaccine. Forsows,61.28%of them use classical PRRS live vaccine; however, only13.7%of them use highlypathogenic PRRS live vaccine. For piglets,75.00%of them use classical PRRS live vaccine, and 15.58%of them use highly pathogenic PRRS live vaccine. Satisfaction survey results showed thatmore than79.6%of swine farms are satisfied with the use of classical PRRS live vaccine, however,less than63.3%of swine farms are satisfied with the use of highly pathogenic PRRS live vaccine.More than79.95%of swine farms approved the safety of classic PRRS live vaccine, but less than67.31%of swine farms approved the safety of the highly pathogenic PRRS live vaccine. Thesurvey results demonstrated that classic PRRS live vaccine is currently the most widely used andmost trusted PRRS vaccine for users.