| Porcine circovirus(PCV) belongs to the family Circoviridae, genus Circovirus. Circoviruses are small single-stranded DNA viruses that infect birds and pigs. PCV are distributed worldwide and poses a considerable threat to the health and reproduction of pigs. There are two types of PCV, type 1(PCV1) and type 2(PCV2). PCV1 was first identified as a contaminant in the PK-15 cell line. Experimental infection of pigs with PCV1 resulted in no clinical signs, and thus PCV1 is considered to be non-pathogenic. In contrast, PCV2 infection of pigs results in diverse clinical syndromes, including diseases such as porcine multi-systemic wasting syndrome(PMWS), porcine dermatitis and nephropathy syndrome(PDNS), porcine respiratory disease complex(PRDC), reproductive failure, and more. Consequently, the majority of research has been focused on PCV2. PCV2 has now evolved into three major groups, 2a, 2b and 2c. PCV2 of group 2c has only been isolated in Denmark.During September 2013 to December 2015, we carried out an epidemiological surveillance on pigs in Guangdong province. The seropositive rate of PCV2 in these pigs was 71.89% by ELISA, indicating that PCV2 infection is common in Guangdong province. Five PCV2 strains were also isolated from pigs. The nucleotide homology of these isolateswasfrom 95.2% to 99.2%, and was between 94.9% to 99.7% nucleotide homology when compared to reference strains(ie. 2013 Guangdong isolates, 2008 Beijing isolates, 2005 Shandong isolates, and 2008 Guangxi isolates). Our results indicate that the origin of PCV2 in Guangdong province is complex.In our study, the codon usage bias of PCV was investigated. The result revealed that codon usage bias indeed existed in both subtypes of PCV.The results showed that the average ENC value of PCV was greater than 50, indicating that the codon usage bias of PCV was low.The mutation bias dominated over natural selection in shaping the codon usage bias of PCV1.Meanwhile, in PCV2, the roles of mutation bias and natural selectionwere equal.The result showed that ORF1, ORF2 and ORF3 contributed to the codon usage bias of PCV to a degree.Analysis of PCV codon bias beneficial to in-depth understanding of the genetic evolution of the virus and the way the codon usage pattern, so as to provide reference for the prevention and control of the virus.Micro RNAs(mi RNAs) are a class of endogenous non-coding small RNAs that are 18-22-nucleotides in length. mi RNAs regulate gene expression at the post-transcriptional level. To investigate the pathogenic mechanism of PCV2 infection, we used a high throughput approach to sequence mi RNA libraries from the PK15 cell line before and after infection with PCV2 to identify mi RNAs involved in PCV2 infection. Eighteen known mi RNAs were differentially expressed between infected and control cells, which include 12 upregulated and 6 downregulated mi RNAs. Eight new mi RNAs were differentially expressed between infected and control cells, which include 6 upregulated and 2 downregulated mi RNAs.Through our network analysis, we discovered an important mi RNA(ssc-mi RNA-328), two important genes(ATG and JUN(AP1)), and an important pathway(Toll-like receptor signaling pathway) that play a major role in PCV2 infection. Furthermore, the host innate immune system plays a substantial role in PCV2 infection of PK15 cells.In summary, epidemiological surveillance and genetic evolution of PCV2 were performed in Guangdong province and the codon usage bias of PCV was analyzed, which will contribute to better understanding of PCV2 evolution. The present study also examined the expression profiles of mi RNAs in PK15 cells infected with PCV2, which will contribute to understanding PCV2 pathogenesis. These findings will further our understanding of the host-PCV2 interaction, contributing to the prevention and control of PCV2 in pigs. |
PDF Full Text Request