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Porcine circovirus-associated disease (PCVAD) caused by porcine circovirus type 2 (PCV2) is an important disease in the global pig industry. Dendritic cells (DCs) are the primary immune cells capable of initiating adaptive immune responses as well as major target cells of PCV2. To determine whether PCV2 affects the immune functions of DCs, we evaluated the expression of endocytosis and co-stimulatory molecules on DCs (CD11c super(+)) from PCV2-infected mouse spleen by flow cytometry (FCM). We also analyzed the main cytokines secreted by DCs (CD11c super(+)) and activation of CD4 super(+) and CD8 super(+) T cells by DCs (CD11c super(+)) through measurement of cytokine secretion, using ELISA. Compared with control mice, PCV2 did not affect the endocytic activity of DCs but it significantly enhanced TNF- alpha secretion and markedly decreased IFN- alpha secretion. Subsets of CD40 super(+), MHCII super(+) CD40 super(+) and CD137L super(+) CD86 super(+) DCs did not increase obviously, but MHCII super(+) CD40 super(-) and CD137L super(-) CD80 super(+)/CD86 super(+) DCs increased significantly in PCV2-infected mouse spleen. Under the stimulation of DCs from PCV2-infected mouse, secretion of IFN- gamma by CD4 super(+) and CD8 super(+) T cells and of IL-12 by CD8 super(+) T cells was significantly lower than in control mice, while secretion of IL-4 by CD4 super(+) T cells was remarkably higher. These results indicate that PCV2 modulates cytokine secretion and co-stimulatory molecule expression of DCs, and alters activation of CD4 super(+) and CD8 super(+) T cells by DCs. The immunomodulatory effects of PCV2 on DCs might be related to the host's immune dysfunction and persistent infection with this virus.

Porcine circoviruses (PCVs), including porcine circovirus 2 (PCV2) and porcine circovirus 3 (PCV3), have been associated with clinical syndromes in swine, resulting in significant economic losses. To better understand the epidemiology and clinical relevance of PCV2 and PCV3, this study analyzed a dataset comprising diagnostic data from six veterinary diagnostic laboratories (VDLs) in the United States of America. The data comprised of polymerase chain reaction (PCR) test results, sample type, and age group for PCV2 and PCV3 submissions from 2002–2023. Findings indicated a decrease in the percentage of PCV2-positive submissions after introducing a commercial PCV2 vaccine in 2006 and a resurgence in positivity after 2018, particularly in breeding herds, associated with an increased number of submissions using processing fluid samples. After its first report in the U.S. in 2016, PCV3 detection had an upward trend in the percentage of positive cases, peaking in spring 2023. PCV3 detection was more frequent in adult/sow farms, while PCV2 was more frequently detected in the wean-to-market category. An additional analysis used results from tissue diagnostic data from 2019–2023 from one VDL to associate PCR cycle threshold (Ct) values with the probability of confirming a PCV2 or PCV3 disease diagnosis confirmation. An interpretative PCR Ct cutoff for PCV2 and PCV3 diagnoses was assessed based on the logistic regression model associating Ct values with the presence of tissue lesions. The analysis considered only cases tested for PCV2 and PCV3 by PCR with tissue evaluations by diagnosticians. An interpretative Ct cutoff of 22.4 for PCV2 was associated with a high probability of confirming a diagnosis of PCV2 clinical disease through histopathology. For PCV3, the interpretative cutoff with the highest performance was 26.7. These findings contribute to the ongoing efforts to monitor and understand the clinical relevance of PCV2 and PCV3 PCR results, identifying potential disease challenges.

The family Circoviridae contains viruses with covalently closed, circular, single-stranded DNA (ssDNA) genomes, including the smallest known autonomously replicating, capsid-encoding animal pathogens. Members of this family are known to cause fatal diseases in birds and pigs and have been historically classified in one of two genera: Circovirus , which contains avian and porcine pathogens, and Gyrovirus , which includes a single species ( Chicken anemia virus ). However, over the course of the past six years, viral metagenomic approaches as well as degenerate PCR detection in unconventional hosts and environmental samples have elucidated a broader host range, including fish, a diversity of mammals, and invertebrates, for members of the family Circoviridae . Notably, these methods have uncovered a distinct group of viruses that are closely related to members of the genus Circovirus and comprise a new genus, Cyclovirus . The discovery of new viruses and a re-evaluation of genomic features that characterize members of the Circoviridae prompted a revision of the classification criteria used for this family of animal viruses. Here we provide details on an updated Circoviridae taxonomy ratified by the International Committee on the Taxonomy of Viruses in 2016, which establishes the genus Cyclovirus and reassigns the genus Gyrovirus to the family Anelloviridae, a separate lineage of animal viruses that also contains circular ssDNA genomes. In addition, we provide a new species demarcation threshold of 80% genome-wide pairwise identity for members of the family Circoviridae , based on pairwise identity distribution analysis, and list guidelines to distinguish between members of this family and other eukaryotic viruses with circular, ssDNA genomes.

Circovirids have a circular single-stranded DNA genome packed into a small icosahedral capsid. They are classified within two genera, Circovirus and Cyclovirus, in the family Circoviridae (phylum Cressdnaviricota, class Arfiviricetes, order Cirlivirales). Over the last five years, a number of new circovirids have been identified, and, as a result, 54 new species have been created for their classification based on the previously established species demarcation criterion, namely, that viruses classified into different species share less than 80% genome-wide pairwise sequence identity. Of note, one of the newly created species includes a circovirus that was identified in human hepatocytes and suspected of causing liver damage. Furthermore, to comply with binomial species nomenclature, all new and previously recognized species have been (re)named in binomial format with a freeform epithet. Here, we provide a summary of the properties of circovirid genomes and their classification as of June 2024 (65 species in the genus Circovirus and 90 species in the genus Cyclovirus). Finally, we provide reference datasets of the nucleotide and amino acid sequences representing each of the officially recognized circovirid species to facilitate further classification of newly discovered members of the Circoviridae.

Porcine circovirus type 2 (PCV2) is an economically important swine pathogen and, although small, it has the highest evolution rate among DNA viruses. Since the discovery of PCV2 in the late 1990s, this minimalistic virus with a 1.7 kb single-stranded DNA genome and two indispensable genes has become one of the most important porcine pathogens, and presently is subjected to the highest volume of prophylactic intervention in the form of vaccines in global swine production. PCV2 can currently be divided into five different genotypes, PCV2a through PCV2e. It is well documented that PCV2 continues to evolve, which is reflected by changes in the prevalence of genotypes. During 2006, commercial vaccines for PCV2 were introduced on a large scale in a pig population mainly infected with PCV2b. Since 2012, the PCV2d genotype has essentially replaced the previously predominant PCV2b genotype in North America and similar trends are also documented in other geographic regions such as China and South Korea. This is the second major PCV2 genotype shift since the discovery of the virus. The potential increase in virulence of the emergent PCV2 genotype and the efficacy of the current vaccines derived from PCV2a genotype against the PCV2d genotype viruses has received considerable attention. This review attempts to synthesize the understanding of PCV2 biology, experimental studies on the antigenic variability, and molecular epidemiological analysis of the evolution of PCV2 genotypes.

Background Porcine circovirus 2 causes different clinical syndromes resulting in a significant economic loss in the pork industry. Three pigs with unexplained cardiac and multi-organ inflammation that tested negative for PCV2 and other known porcine pathogens were further analyzed. Methods Histology was used to identify microscopic lesions in multiple tissues. Metagenomics was used to detect viral sequences in tissue homogenates. In situ hybridization was used to detect viral RNA expression in cardiac tissue. Results In all three cases we characterized the genome of a new circovirus we called PCV3 with a replicase and capsid proteins showing 55 and 35 % identities to the genetically-closest proteins from a bat-feces associated circovirus and were even more distant to those of porcine circovirus 1 and 2. Common microscopic lesions included non-suppurative myocarditis and/or cardiac arteriolitis. Viral mRNA was detected intralesionally in cardiac cells. Deep sequencing in tissues also revealed the presence of porcine astrovirus 4 in all three animals as well as rotavirus A, porcine cytomegalovirus and porcine hemagglutinating encephalomyelitis virus in individual cases. Conclusion The pathogenicity and molecular epidemiology of this new circovirus, alone or in the context of co-infections, warrants further investigations.

Background Diseases caused by polyomaviruses and circoviruses in parrots were first described in the 1980s. Then they began to be diagnosed in other orders of birds, including Passeriformes, such as Atlantic canaries ( Serinus canaria ) and estrildid and fringillid finches. Over time, these viruses have also been found in an increasing number of captive and wild passerine species. The aim of the study was to assess the occurrence of these viruses in captive and wild Passeriformes in Poland, and the transmission of polyomaviruses and circoviruses through eggs in Atlantic canaries and Bengalese munias ( Lonchura striata domestica ). Results Nested PCR tests for avian polyomavirus (APyV) and circovirus (CV) were carried out on organ samples from 331 captive and wild birds belonging to 45 species, necropsied between 2006 and 2024. Additionally, 112 samples of eggs and dead chicks of Atlantic canaries and Bengalese munias from two aviaries with breeding problems were examined. Positive PCR results for APyV were found in 98 birds (29.6%), while CV DNA was detected in 152 birds (45.9%). In 104 wild birds examined, APyV was found in 13 (12.5%) and CV in 35 (33.7%) individuals. In 227 captive birds, APyV was found in 85 (37.4%) and CV in 117 (51.5%) individuals. Co-infections with both viruses were found in 25.1% of captive birds and 7.7% of wild birds. Negative results for both APyV and CV were found in 145 (43.8%) birds tested. In Atlantic canaries, CV DNA was identified in 79% of unfertilized eggs and 59% of embryos examined. In Bengalese munias, CV DNA was identified in 62.5% of unfertilized eggs and in all chicks examined. APyV DNA was not detected in eggs or embryos of canaries and Bengalese munias, nor in any Bengalese munia chicks or canary chicks younger than 7 days. Conclusions Avian polyomaviruses and circoviruses are widespread in the population of captive and wild passerines in Poland, and a higher percentage of birds are infected with circovirus than with polyomavirus. Co-infections are more commonly observed in captive passerine birds than in wild passerine birds. Vertical transmission occurs for circoviruses, but not for polyomaviruses, in Atlantic canaries and Bengalese munias.

Circoviruses cause diseases in a wide range of hosts, including avian species. One of the most studied circoviruses is beak and feather disease virus (BFDV), which has spread worldwide due to global trade of birds and characteristics of the virus that allow it to persist in the environment. The Eurasian griffon vulture (Gyps fulvus) is one of the largest birds in the world and is among several vulture species that are considered endangered today, and currently the only remaining vulture species in Croatia. Several juvenile Eurasian griffon vultures undergoing rehabilitation at the Beli Visitor Centre and Rescue Centre for Griffon Vultures on the island of Cres, Croatia, had feather lesions similar to those caused by BFDV in psittacine birds. Signs included partially retained feather sheaths, discoloration and circumferential constrictions of the feather shafts, gnawed feather tips, keratin and egg deposits near the feather shafts, as well as feather breakage and spontaneous feather loss. Feather samples were collected for molecular detection of viral pathogens and macroscopic detection of ectoparasites; blood samples were taken for complete blood count (CBC), biochemical analysis and oxidative stress analysis. The molecular analysis confirmed a circovirus infection, which was supported by the blood analyses indicating a viral infection. The collected ectoparasites were identified as chewing lice - Colpocephalum turbinatum and Falcolipeurus quadripustulatus , which have previously been detected in Eurasian griffon vultures. To our knowledge, this is the first report of circovirus infection in Eurasian griffon vultures. Considering that circoviruses are highly contagious, very resistant and easily transmissible, it is extremely important to perform continuous monitoring in order to improve the breeding and survival conditions of Eurasian griffon vulture populations worldwide.

Porcine circovirus type 3 (PCV3) capsid protein (Cap) is a key antigen for immunological studies and vaccine development. Different optimized PCV3 ORF2 sequences were used to construct six baculovirus transfer plasmids, with the pOET1.1-based design yielding the highest Cap level. Cap expression was confirmed by Western blot, IPMA and IFA. Recombinant baculovirus amplification was optimized, achieving the highest titer at an MOI of 0.1 with a 72 h harvest to 10 TCID /0.1 mL, while maximal Cap production was obtained at an MOI of 0.1 with a 96 h harvest. PCV3 Cap virus-like particles (VLPs) were purified by sucrose density-gradient ultracentrifugation and cation-exchange chromatography, and TEM revealed spherical particles of approximately 17-20 nm. In mice, VLP immunization induced increasing antigen-specific IgG from day 14. Immunization increased both IgG1 and IgG2a without a significant difference, and post-immunization serum specifically recognized PCV3-positive passaged PK-15 cells in an indirect immunofluorescence assay. In splenic lymphocytes, IFN-γ, TNF-α, IL-4, and IL-10 mRNA levels were significantly upregulated ( < 0.01). Moreover, pig challenge data supported the protective potential of PCV3 Cap VLPs in the natural host. In our study, Cap assembled into VLPs and induced immune responses, providing a basis for PCV3 subunit vaccine development.

This study was aimed to investigate the frequency of PiCV recombination, the kinetics of PiCV viremia and shedding and the correlation between viral replication and host immune response in young pigeons subclinically infected with various PiCV variants and kept under conditions mimicking the OLR system. Fifteen racing pigeons originating from five breeding facilities were housed together for six weeks. Blood and cloacal swab samples were collected from birds every seven days to recover complete PiCV genomes and determine PiCV genetic diversity and recombination dynamics, as well as to assess virus shedding rate, level of viremia, expression of selected genes and level of anti-PiCV antibodies. Three hundred and eighty-eight complete PiCV genomes were obtained and thirteen genotypes were distinguished. Twenty-five recombination events were detected. Recombinants emerged during the first three weeks of the experiment which was consistent with the peak level of viremia and viral shedding. A further decrease in viremia and shedding partially corresponded with IFN-γ and MX1 gene expression and antibody dynamics. Considering the role of OLR pigeon rearing system in spreading infectious agents and allowing their recombination, it would be reasonable to reflect on the relevance of pigeon racing from both an animal welfare and epidemiological perspective.