Porcine circovirus type 2 (PCV2) infection can lead to porcine circovirus-associated disease (PCVAD), causing great economic losses to the global swine industry. Conventional vaccination programs are a major measure in the prevention and control of this disease. Currently, there are 5 commercially available PCV2 vaccines in the international market and 10 kinds commercially available PCV2 vaccines in the Chinese market that confer good efficacy against this virus by alleviating clinicopathological manifestations and enhancing growth performance in pigs. In addition, diverse experimental PCV2 vaccines with protective efficiency have been developed, including attenuated chimeric, nucleic acid, subunit, multivalent, and viral-vectored vaccines. These experimental vaccines have been shown to be relatively effective in improving the efficiency of pig production and simplifying prevention procedures. Adjuvants can be used to promote vaccines with higher protective immunity. Herein, we review the application of multiple commercial vaccines over the years and research advances in experimental vaccines, which provide the possibility for the development of superior vaccines to successfully prevent and control PCV2 infection in the future.

Infectious bursal disease virus (IBDV), an Avibirnavirus, is the pathogen of infectious bursal disease, which is a severely immunosuppressive disease in 3–15‐week‐old chickens. Different phenotypes of IBDV, including classical, variant, very virulent (vv) and attenuated IBDV, have been reported in many chicken‐rearing countries worldwide. Here, we isolated and identified a naturally reassortant and recombinant IBDV (designated GXB02) from 20‐day‐old chickens with clinicopathological changes of infectious bursal disease (IBD) in Guangxi Province, China. Whole genomic sequencing showed that the strain GXB02 simultaneously has both reassortant and recombinant characteristics with segments A and B being derived from recombinant intermediate vaccine strain and classic strains of IBDV. Segment A of strain GXB02 was incorporated into the skeleton of an intermediate IBDV vaccine strain (W2512), where the breakpoints of two recombinant events located at nucleotide positions 1468 and 1648 were replaced by reassortant vvIBDV (PK2) and vvIBDV (D6948) of segment A, respectively. We used this GXB02 strain to inoculate 21‐day‐old specific‐pathogen‐free chickens to evaluate its pathogenicity. Strain GXB02 has clinicopathologic characteristics of IBD with severe bursal lesions, as evidenced by necrosis, depletion of lymphocytes, and follicle atrophy, indicating that reassortment with classical strains in segment B or/and recombination with very virulent strains increased pathogenicity of the strain GXB02 in chickens. These findings provide important insights into the genetic exchange between classic and attenuated strains of IBDV with two recombinant events occurring at the intermediate derivative segment A with vvIBDV strains, thereby increasing the difficulty of prevention and control of IBD due to novel reassortant–recombinant strains.

Tembusu virus (TMUV) can induce severe egg drop syndrome in ducks, causing significant economic losses. In this study, the possible origin, genomic epidemiology, and transmission dynamics of TMUV were determined. The time to the most recent common ancestor of TMUV was found to be 1924, earlier than that previously reported. The effective population size of TMUV increased rapidly from 2010 to 2013 and was associated with the diversification of different TMUV clusters. TMUV was classified into three clusters (clusters 1, 2, and 3) based on the envelope (E) protein. Subcluster 2.2, within cluster 2, is the most prevalent, and the occurrence of these mutations is accompanied by changes in the virulence and infectivity of the virus. Two positive selections on codons located in the NS3 and NS5 genes (591 of NS3 and 883 of NS5) were identified, which might have caused changes in the ability of the virus to replicate. Based on phylogeographic analysis, Malaysia was the most likely country of origin for TMUV, while Shandong Province was the earliest province of origin in China. This study has important implications for understanding TMUV and provides suggestions for its prevention and control.

Porcine circovirus type 3 (PCV3) is a newly identified virus associated with porcine dermatitis and nephropathy syndrome (PDNS) and multisystemic inflammatory responses in pigs. Recent studies suggests that PCV3 originated from bat circoviruses; however, the origin time, mode of spread, and geographic distribution of PCV3 remain unclear. In this study, the evolutionary origin, phylodynamics, and phylogeography of PCV3 were reconstructed based on the available complete genome sequences. PCV3 showed a closer relationship with bird circovirus than with bat circovirus, but their common ancestor was bat circovirus, indicating that birds may be intermediate hosts for the spread of circoviruses in pigs. Using the BEAST and phylogenetic analyses, three different clades of PCV3 (PCV3a, PCV3b, and PCV3c) were identified, with PCV3a being the most prevalent PCV3 clade. Further studies indicated that the earliest origin of PCV3 can be traced back to 1907.53–1923.44, with a substitution rate of 3.104 × 10–4 to 6.8524 × 10–4 substitution/site/year. A phylogeographic analysis highlighted Malaysia as the earliest location of the original PCV3, which migrated to Asia, America, and Europe. Overall, this study provides novel insights into the evolutionary origin, spread mode, and geographic distribution of PCV3, which will facilitate the prevention and control of PCV3 epidemics in the future.

Entry of virus into cells represents the initiation of a successful infection. As an emerging pathogen of porcine vesicular disease, clarification of the process of SVV entry into cells enables us to better understand the viral life cycle and pathogenesis.