Recently, the emergence of HP-PRRSV (Highly Pathogenic porcine reproductive and respiratory syndrome virus) and the exacerbation of mixed infections of PRRSV and PCV have resulted in significant economic losses for the Chinese pig industry. This study collected a total of 226 samples suspected of infection with the aforementioned viruses from diverse pig farms in seven urban districts of central and northern Guangdong Province between 2020 and 2022. The positive rates of PRRSV, PCV2, and PCV3 in the samples were 33.2%, 37.6%, and 7.5%, respectively, and there were various mixed-infection scenarios present in the samples. This study successfully isolated multiple strains of PRRSV2 and PCV2 from their positive samples, and obtained the gene sequences of six PCV3 (ORF1 + ORF2) from samples. The associated sequences obtained were subjected to bioinformatic analysis and revealed the following:Predominantly prevalent strains of PRRSV in Guangdong Province include HP-PRRSV and NADC30-like variants, whereas PCV2 is primarily represented by the 2b and 2d subtypes. Specifically, the amino acid variation patterns exhibited by the PRRSV GP5 and NSP2 proteins of the strains sg_2108, qy_2008, and fs_2108 under environmental selective pressure are remarkably similar to the characteristics of Highly Pathogenic PRRSV; thus, it is inferred that they may possess higher virulence. The detected PCV3 strains were predominantly concentrated within the PCV3a-IM branch. All PRRSV strains involved in this study are wild-type-PRRSV (wt-PRRSV), comprising three recombinant strains and seven highly virulent strains. Among these strains, the ORF1a gene exhibited the highest variability in their genomes. Environmental selective pressure may enhance the virulence and immune evasion capabilities of PRRSV and drive mutations in the Cap proteins of PCV2 and PCV3. Conversely, PCV2 and PCV3 strains demonstrated greater stability in genetic evolution. In conclusion, this study enhances the epidemiological data regarding PRRSV, PCV2, and PCV3 in Guangdong Province, China, and is significant for the surveillance, prevention, and active control of these three diseases.
Keywords: epidemiological investigation; genetic variation analysis; porcine circovirus type 2 (PCV2); porcine circovirus type 3 (PCV3); porcine reproductive and respiratory syndrome virus (PRRSV).