A B S T R A C TPorcine circovirus type 3 (PCV3) is an emerging circovirus species associated with several diseases. The study aimed to investigate the frequency of porcine circovirus 3 (PCV3) and its coinfection with canine parvovirus type 2 (CPV-2) in dogs in the Guangxi province from 2015 to 2017, China, and to examine the genome diversity of PCV3. Using polymerase chain reaction (PCR) amplification and sequencing, 96 of 406 (23.6%)samples were positive for PCV3, 38 out of 406 (9.4%) samples were coinfected with both PCV3 and CPV-2. The CPV-positive rate was significantly higher in the PCV3-positive samples than in the non-PCV3 samples, and the difference was extremely significant (P < 0.01). The complete genome (n=4) and ten capsid genes (n=10) of PCV3 were sequenced. Multiple sequence alignment results showed that these sequences shared 98.5-100% nucleotide similarity with the reference genome sequence and 97.5-100% nucleotide similarity with the reference capsid gene sequence. PCV3 was classified into two different genotypes, according to phylogenetic analysis based on the whole genome. These strains were clustered in PCV3a, showing a close relationship with PCV3-US/SD2016. Surprisingly, we separately analyzed these PCV3 strains from the Guangxi province and found that the dog and pig PCV3 are from different branches. In summary, this was the first seroprevalence and genetic investigation of PCV3 in dogs in the Guangxi province, China, and the first complete genome PCV3 from dogs obtained in the world. The results provide insights into the epidemiology and pathogenesis of this important virus.

Parvoviruses are a diverse group of viruses that infect a wide range of animals and humans. In recent years, advances in molecular techniques have resulted in the identification of several novel parvoviruses in swine. In this study, porcine parvovirus 7 (PPV7) isolates from clinical samples collected in Guangxi, China, were examined to understand their molecular epidemiology and co-infection with porcine circovirus type 2 (PCV2). In this study, among the 385 pig serum samples, 105 were positive for PPV7, representing a 27.3% positive detection rate. The co-infection rate of PPV7 and PCV2 was 17.4% (67/385). Compared with the reference strains, we noted 93.9%-97.9% similarity in the NS1 gene and 87.4%-95.0% similarity in the cap gene. Interestingly, compared with the reference strains, sixteen of the PPV7 strains in this study contained an additional 3 to 15 nucleotides in the middle of the cap gene. Therefore, the Cap protein of fourteen strains encoded 474 amino acids, and the Cap protein of the other two strains encoded 470 amino acids. However, the Cap protein of the reference strain PPV7 isolate 42 encodes 469 amino acids. This is the first report of sequence variation within the cap gene, confirming an increase in the number of amino acids in the Cap protein of PPV7. Our findings provide new insight into the prevalence of PPV7 in swine in Guangxi, China, as well as sequence data and phylogenetic analysis of these novel PPV7 isolates.