Studies On Molecular Epidemiology Of PCV2and The Preparation Of Chimeric PCV2Virus

Porcine circovirus type2(PCV2) is a small non-enveloped virus with a single-stranded circular DNA genome of approximately1.8kb in size in the genus circovirus, circoviridae family. According to the sequence analysis, PCV2contains three main genotypes of PCV2a, PCV2b and PCV2c. Furthermore, PCV2a can be divided into five subtypes of2A through2E, while PCV2b has three subtypes of1A, IB and1C. PCV2has been confirmed as the primary infectious agent in PCV-associated diseases (PCVAD) which encompasses clinical signs such as systemic infections, pneumonia, enteritis, reproduction disorders, porcine dermatitis nephropathy syndrome, post-weaning multi-systemic wasting syndrome (PMWS) as well as asthenia syndrome symptoms. Currently, the PCV2infections have been increasing in China, resulting in increasing morbidity and mortality in swine populations and significant economic losses in the swine industry worldwide as well.To investigate the infection of PC V2in farms, total of245pig tissue samples from Shandong, Fujian, Anhui, Hebei, Henan, Guangxi, Liaoning and Hubei Provinces were detected by use of polymerase chain reaction (PCR) with1pairs of specific primers against PCV2. The result showed that the infection rate of PCV2, was73.47%. Among the61strains of PCV2, and existed three genotypes of PCV2a, PCV2b1C and PCV2blA1B of8,19and34, respectively.To further study natural recombination of PCV2in the field, the complete genomic sequences of39isolates strains of PCV2were compared. In addition, natural recombination events were analyzed with recombinant analysis software. Three natural recombination strains of PCV2were identified, i.e. AHF13and AHF14derived from the recombination between PCV2a and PCV2b1B, while AHF9was recombinated from PCV2b1A1B and PCV2blC. And the recombination area of AHF13and AHF14was located in ORF2while the AHF9was in ORF1.Recombinant PCV1-2and PCV2-1viruses were constructed by replacing the PCVI ORF2and ORF2ori with those of PCV2isolates with the PCV1as backbone. The genetic stability of the PCV1-2and PCV2-1. The recombiant viruses were obtained by transfection into PK15cell line followed by15continuous passages. Sequence analyses did not reveal any sequence change. Two recombinant viruses were inoculated intraperitoneally into BALB/c mice, and there was no mutation in the whole genomic sequences after2passages. The study might supply a candidate vaccine for PCV2control.