Abstract: Porcine circoviruse (PCV) is one of the fastest single-stranded DNA viruses known to evolve,and can be classified into four genotypes (PCV1 to PCV4),of which PCV2 has an evolutionary rate of 1.2×10^-3 substitutions/sites/year,which is close to that of RNA viruses.PCV4 is a newly identified genotype with 43.2% to 51.5% similarity to the genomes of other PCVs.PCV1 is not pathogenic,and the remaining genotypes can infect pigs of all ages,causing immunosuppression-related diseases with various clinical manifestations,which has become one of the most important factors constraining the development of contemporary pig farming.Available studies have shown that PCVs are widespread and highly contagious in swine and frequently detected in ruminants,rodents,canines,arthropods and other species,posing a risk of cross-species transmission and warranting great attention.To gain a deeper understanding of the evolution,origin and cross-species transmission potential of PCVs,the authors summarize the detection of PCVs in different species and the potential transmission pathways,which will provide a reference for revealing their evolution,host adaptation studies and prevention and control strategies.

Key words: Porcine circovirus (PCV); genetic evolution; host diversity; pathogenicity