Isolation And Identification Of Porcine Circovirus Type2in Jiangsu Province And The Protective Efficacy Induced By Chimeric PCV1-2Inactivated Vaccine Emulsified With206Adjuvant

Porcine circovirus associated disease (PCVAD) is mainly caused by the pathogen of porcine circovirus type2(PCV2). It is an important emerging disease following the porcine reproductive and respiratory syndrome (PRRS). Since PCV2was isolated for the first time by Clark in1997, the disease has caused a huge economic loss to the worldwide pig industry. At the20th International Pig Veterinary Society Congress (20th IPVS) in2008, it was classfied as the number one disease to affect the development of the pig industry. Since PCV2-specific antibody was first reported in pigs in2000by Hongwu Lang in China, then PCV2infection was reported in all around the country.The purpose of this study is to investigate the PCV2infection situation in Jiangsu province, and provide effective information for prevention and control of related diseases. Dulac cell was transfected with the chimeric porcine circovirus type1-2DNA clone constructed in our laboratory by electroporation to obtain chimeric PCV1-2virus. Commercial pigs without PCV2maternal antibodies were injected with the inactivated chimeric PCV1-2vaccine emulsified with206adjuvant followed by the challenge with wild-type PCV2strain. In order to evaluate the validity of the candidate vaccine in prevention for disease caused by PCV2, comparison between vaccinated/challenged pigs and challenged-only pigs was carried out by indirect immunofluorescent assay (IFA) antibody, neutralizing antibody determination, macroscopic and histological lesions, viral loads and growth rates of pigs mentioned above.1Isolation and identification of porcine circovirus type2strains in Jiangsu provinceThe lymphnode and lung tissues of pigs from a slaughter house in Yangzhou were collected and detected by PCR test. At the same time, porcine circovirus type2was isolated and identified from PCV2positive samples, consequently, five PCV2isolates were obtained, and their whole genomes were sequenced.Sequencing results showed that the five PCV2isolates were all1767bp in genome size and705bp in ORF2size. Nucleotide homogenecity of complete genome of the isolated strains ranged from99.6%-99.7%. Phylogenetic analysis revealed that the five PCV2isolates all belonged to PCV2group1(PCV2b). The isolated strains were closed to each other and belonged to the same narrow branch and closed to PCV2group1C strain of Guangdong, China and Netherlands, respectively, refer to the phylogenetic tree. The results demonstrated that PCV2group1has become prevalent group in Jiangsu recently. These achievements will help to understand the epidemiology and prevent/control of PCV2infection, and give the insight into genetics and evolution of PCV2strains in Jiangsu province.2Chimeric PCVI-2inactivation vaccine evaluated in commercial pig without PCV2maternal antibodies for its protective efficacy against PCV2infectionIn this study, Dulac cells were electroporated with the chimeric porcine circovirus type1-2DNA clone constructed in our laboratory using electroporation apparatus to obtain chimeric PCV1-2virus by passage cultures. The inactivated vaccine of chimeric PCV1-2virus emulsified with206adjuvant were made as immunogen to inject42-day-old commercial pigs without PCV2maternal antibodies at1st and21st day respectively. The challenge of wild-type PCV2strain was followed at35th day.By35days post-vaccination (DPV), all vaccinated pigs had seroconversion to antibody against PCV2and developed high titer of the indirect immunofluorescent assay (IFA) antibody and neutralizing antibody at1/15～1/20. By21days post-challenge, gross and microscopic lesions of lymph nodes and lungs in non-vaccinated but challenged pigs were significantly more severe than those found in vaccinated groups. There were multinucleated giant cells, large number of eosinophilia and lymphocyte depletion in lymph nodes in non-vaccinated but challenged pigs. There were no multinucleated giant cells and less lymphocyte depletion in vaccinated pigs. By quantitative PCR (qPCR), PCV2viral copy loads detected in lymph nodes in non-vaccinated but challenged pigs were5.566～0.432, in vaccinated pigs with104.0TCID50,105.0TCID50,106.0TCID50were4.469±1.023,4.434±0.716,3.521±0.958, respectively Comparison between vaccinated pigs with105.0TCID50,106.0TCID50and non-vaccinated but challenged pigs the difference was significant (P<0.05). The results illuminated that the inactivated chimeric PCV1-2could induce protective immunity against PCV2infection effectively.