Frequency detection of porcine circovirus-like viruses in pigs with porcine respiratory disease.

The emergence of the circular replication-associated protein (Rep) encoding single-stranded (CRESS) DNA viruses in different hosts has been associated with serious diseases, such as porcine diarrhea. The prevalence and pathogenicity of porcine circovirus-like virus (Po-Circo-like virus (PCLV)), a member of CRESS DNA virus, has not been fully illustrated. In order to understand the frequency of PCLV in pigs with respiratory disease, 519 healthy tissues (268 lungs, 201 lymph nodes and 50 hearts) and 380 tissues (212 lungs, 124 lymph nodes and 44 hearts) diagnosed with respiratory disease were collected for analyzing the prevalence of the PCLV infection using the Tag-Man qPCR assay. In addition, the complete genome of 43 PCLV strains were then sequenced, which were subsequently to analyze their characteristics. We found that 31.7 % (285/899) samples were tested positive for PCL virus. It is interesting to note that just 9.6 % (50/519) of the healthy samples were tested positive for PCLV, 61.8 % (235/380) of the diseased samples were PCLV positive. Analysis of the full genome of 43 PCLV strains showed that the genome of 42 PCLV strains included two distinct stem-loop structures, but the genome of PCLV FJ5-2020 strain contained no stem-loop structures. A phylogenetic tree analysis based on the Rep protein, PCLV could be classified into four genotypes: PCLVa, PCLVb, PCLVc, and PCLVd. In conclusion, this is the first report that the high frequency of PCLV in association in respiratory diseased pigs. PCLV strains were divided into four new genotypes of PCLV.