Investigation On Molecular Epidemiology Of Type Two Porcine Circovirus(PCV2) In Henan Province

Porcine circovirus type 2(PCV2) not noly be considerded as the causal agent of postweaning multisystemic wasting syndrome(PMWS),it is associated with various other porcine circovirus-associated diseases (PCVAD) .Immunodeficiency is a well-known consequence of PCV2 infection. It often is ignored because of its sub-clinical infection ,so the study of the epidemiology of virus should be further investigated.To understand the genetic heterogeneity and the origin of PCV2 strains in Henan province, 361 samples which were based on clinical signs for PCVAD were detected for PCV2 DNA by PCR test,and 256 samples were positive for PCV2 DNA. Some porcine circovirus 2 strains were isolated from positive samples in Henan province. The complete genome of 11 porcine circovirus 2 strains from Henan province were cloned and sequenced. The complete genome of each isolate is 1767 bp in length. The nucleotide sequences of the 11 strains of PCV2 and other 38 PCV2 and 2 PCV1 sequences published in GenBank were aligned using the CLUSTAL W version 1.7 multiple sequence alignment program. The phylogenetic analysis was performed on the aligned data set and an unrooted tree was constructed using the distance-based neighbor-joining method without correction for multiple substitutions. The result showed that two distinct genotypes of PCV2 exist: American clusters and Europe cluster. However, within the PCV-2 genotype, several minor branches that have been identified appear to be associated with geographic origins. The result indicated that the PCV2 strains in Henan were closely related to each other but also to PCV2 strains in other areas of China ; The PCV2 strains in Henan were included in the Europe cluster . It can be conclued that the PCV2 strains in Henan province may originated with Europe PCV2 ;_Although minor genetic differences do exist among PCV2 strains in different years , the genome of PCV2 strains in Henan province exhibited quite stable genetic homogeneity ; The porcine circovirus-associated disease in Henan province is most likely not due to the emergence of a new genotype of PCV2 .Comparison of complete genome sequence of 11 isolated strains in DNAstar software was carried out, the result showed that there was a 98.0% to 99.7% identity of the complete genomic nucleotides among the 11 Henan strains. What's more, we also analyzed the 3 open reading frames(ORFl,ORF2 and ORF3) and the deduced amino acid sequences in computer. Sequence analysis revealed that ORF1 genes of Henan isolated strains exhibited the variation extent of 97.0 to 99.8% and 96.5 to 99.7% in nucleotide and amino acid respectively. The ORF2 of the 11 strains exhibited the variation extent of 91.3% to 100% and 89.7% to 99.6% in nucleotide and amino acid respectively. Sequence analysis revealed that the variation extent of amino acid was greater for the Cap protein than for the Rep protein. The amino acid sequences alignment of the PCV2 capsid protein identified three major regions of amino acid heterogeneity. Two of which correspond with dominant immunoreactive areas. It may contribute to the change of antigenicity. The conservation of Rep protein may be associated with its function. The ORF3 of the PCV2 Henan strains showed the variation extent of 97.1% to 100% and 84.8% to 99.0% in nucleotide and amino acid respectively.The result demonstrated a low degree of homology of ORF3 protein amino acid sequence. It was presumpted that the variation may contribute to the different pathogenicity.