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

Abstract

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.

Keywords: China; Epizootiology; Porcine circoviruses (PCVs); Wild boar.

Fig. 1

Detection of PCVs infection in the tissue samples of Chinese wild boars collected between 2018 and 2020. A Geographical distribution of wild boars collected in this study and the positive numbers of PCVs DNA in each region. Green, blue and red circles represent PCV1, PCV2, and PCV3-positive regions respectively accompanied with the positive numbers. The number of isolates of PCVs is shown with the corresponding-colored dot. B The positive numbers of PCVs detected in the Chinese wild boars in different years.

Fig. 2

Phylogenetic trees based on the nucleotide sequences of full-length ORF2 genes of PCV1. Phylogenetic analysis was performed using MEGA v7.0 with the maximum likelihood method and 1000 bootstraps replicates, and the best fitting substitution model was Hasegawa-Kishino-Yano. PCV1 strains identified in this study are marked with black triangles (▲).

Fig. 3

Phylogenetic analysis and temporal dynamics of wild boar PCV2 strains. A Phylogenetic tree based on the nucleotide sequences of full-length ORF2 genes of PCV2. Phylogenetic analysis was performed using MEGA v7.0 with the maximum likelihood method and 1000 bootstraps replicates, and the best fitting substitution model was Tamura-Nei model. PCV2 strains identified in this study are marked with black triangles (▲). B Temporal dynamics of different PCV2 genotype strains identified in Chinese wild boars.

Fig. 4

Phylogenetic analysis of wild boar PCV3 strains with the reference strains based on the nucleotide sequences of full-length ORF2 genes of PCV3. Phylogenetic analysis was performed using MEGA v7.0 with the maximum likelihood method and 1000 bootstraps replicates, and the best fitting substitution model was Hasegawa-Kishino-Yano. The genotype-specific amino acid residues in Cap proteins of PCV3 strains were attached with the phylogenetic tree. PCV3 strains identified in this study are marked with black triangles (▲).

Fig. 5

Alignment of deduced amino acid sequences of PCV3 Cap proteins. Sequence comparison was performed using CLC Sequence Viewer 8 software. The major amino acid mutations are displayed in a red vertical box. Red horizontal boxes indicate the strains identified in this study.