Molecular characterization of porcine circovirus 2 isolated from diseased pigs co-infected with porcine reproductive and respiratory syndrome virus

Postweaning multisystemic wasting syndrome (PMWS), characterized by growth retardation, paleness of the skin, dyspnea, and increased mortality rates [1,2], was first described in Canada in 1991, and is now widespread throughout swine production areas of the world [3,4]. The genome of PCV is a single-stranded circular DNA of about 1.76 kb. ORF1 encodes the Rep proteins involved in virus replication and is highly conserved among isolates [5]. ORF2 encodes a 234 amino acid (aa) Cap protein, which is the main structural protein and also the major antigen inducing neutralizing immune responses [6]. The ORF3 protein is involved in PCV2-induced apoptosis by the caspase-8 and caspase-3 pathways [7]. However, healthy pigs experimentally inoculated with PCV2 developed only mild clinical symptoms [8,9], suggesting that other concomitant factors may be needed for the development of typical clinical PMWS [10,11]. Experimental studies on co-infection with PRRSV and PCV2 resulted in the microscopic lesions associated with PMWS and/or porcine dermatitis and nephropathy syndrome (PDNS), and lead to the development of severe disease [12].In may 2008, severe disease, known as ''high fever'' occurred in several pig farms in shanghai, leading to a 57% death rate. PRRSV was detected in all the diseased piglets, genome sequence blast showed the strain belongs to genotype 2, 99.4% homologous to the PRRS virus strain JXA1 isolated in China, which has been proved to cause porcine high fever disease with high morbidity and mortality[13]. There was no Porcine Parvovirus (PPV) detected in all the samples, but we detected PCV2 from all the PRRS infected piglets (Figure 1). To investigate the genetic relationship of this newly identified Shanghai PCV2 isolate with existing viruses isolated from other parts of the world, we sequenced the complete genome of the sh0901 strain and carried out phylogenetic and polymorphic analyses.Two pairs of primers were designed according to the published PCV2 geno