Epizootiological surveillance of porcine circoviruses in free-ranging wild boars in China

Four species of porcine circoviruses (PCV1-4) have been reported to circulate in Chinese domestic pigs, while the epizootiology of these viruses in free-ranging wild boars in China remains unknown. In this study, tissue and serum samples collected from diseased or apparently healthy wild boars between 2018 and 2020 in 19 regions of China were tested for the prevalence of PCV1-4 infections. Positive rates of PCV1, PCV2, and PCV3 DNA in the tissue samples of Chinese wild boars were 1.6% (4/247), 58.3% (144/247), and 10.9% (27/247) respectively, with none positive for PCV4. Sequence analysis of viral genome showed that the four PCV1 strains distributed in Hunan and Inner Mongolia shared 97.5%-99.6% sequence identity with global distributed reference strains. Comparison of the ORF2 gene sequences showed that 80 PCV2 strains widely distributed in 18 regions shared 79.5%-100% sequence identity with reference strains from domestic pigs and wild boars, and were grouped into PCV2a (7), PCV2b (31) and PCV2d (42). For PCV3, 17 sequenced strains shared 97.2%-100% nucleotide identity at the genomic level and could be divided into PCV3a (3), PCV3b (2) and PCV3c (12) based on the phylogeny of ORF2 gene sequences. Serological data revealed antibody positive rates against PCV1 and PCV2 of 11.4% (19/167) and 53.9% (90/167) respectively. The data obtained in this study improved our understanding about the epidemiological situations of PCVs infection in free-ranging wild boars in China and will be valuable for the prevention and control of diseases caused by PCVs infection.

Development and application of a quadruplex real-time PCR assay for differential detection of porcine circoviruses (PCV1 to PCV4) in Jiangsu province of China from 2016 to 2020

To date, four species of porcine circoviruses (PCVs), including PCV1-4, have been reported to exist in the clinical cases. Fast and effective differential detection is critical to monitor the infection and co-infection status of PCVs for adopting reliable control strategies. However, currently available methods cannot simultaneously differentiate the four species of PCV strains. In this study, a quadruplex real-time PCR assay based on TaqMan probes was developed for differential detection of PCV1-4. The new quadruplex real-time PCR assay exhibited satisfied specificity, sensitivity, repeatability and reproducibility. In addition, the new assay was applied to the detection of 120 clinical samples collected from 2016 to 2020 in Jiangsu province of China and compared with previously reported PCV1-4 singleplex conventional PCR assays. Based on the clinical performance, the results from the quadruplex real-time PCR and conventional PCR assays showed 100% agreement. A total of 47 samples were detected as PCV positive by the quadruplex real-time PCR assay, including 1, 2, 1 samples were co-infected with PCV1 and PCV4, PCV2 and PCV3, PCV2 and PCV4, respectively. Full-length ORF2 sequencing and phylogenetic analysis supported the real-time PCR results that 5, 34, 8 and 4 of the 51 PCV sequences were PCV1, PCV2, PCV3 and PCV4, respectively. This study provides a promising alternative tool for rapid differential detection of PCVs and confirms the coexistence of all species of PCV1-4 strains in Jiangsu province in recent years.