Advances in Crosstalk between Porcine Circoviruses and Host

Soluble expression and immunogenicity analysis of capsid proteins of porcine circoviruses types 2, 3, and 4

Porcine circoviruses (PCVs) contain four types: PCV1, PCV2, PCV3, and PCV4, all of which can infect pigs. Among them, PCV1 is non-pathogenic, and PCV2 can cause porcine circovirus diseases (PCVD) or porcine circovirus-associated diseases (PCVAD). Although the pathogenicity of PCV3 and PCV4 is still controversial, increasing evidence shows that PCV3 and PCV4 can cause PCV-related disease. However, mixed infection of PCV2, PCV3, and PCV4 with other pathogens often occurs in large-scale pig breeding, bringing severe economic losses to the global pig industry. In this study, the soluble recombinant proteins of PCV2, PCV3, and PCV4 Cap were expressed by the prokaryotic expression system and biotinylated to combine with the Streptavidin magnetic beads, followed by immunogenicity evaluation of the recombinant proteins. Furthermore, we also assessed the efficacy and immunogenicity of trivalent recombinant proteins conjugated with different adjuvants in mice. The results showed that the highly effective anti-PCV serum was successfully prepared, and the recombinant proteins conjugated with different adjuvants produced various degrees of humoral and cellular immunity in mice. Three recombinant proteins are effective immunogens, and the trivalent proteins coupled with the aluminum adjuvant or GM-CSF-CpG for two-dose immunization can stimulate prominent humoral and cellular immunity against PCVs in vivo. The soluble recombinant proteins are the most promising candidate for developing a trivalent vaccine against PCVs (PCV2, PCV3, and PCV4) infection simultaneously.

Circovirus Hepatitis in Immunocompromised Patient, Switzerland

We identified a novel human circovirus in an immunocompromised 66-year-old woman with sudden onset of self-limiting hepatitis. We detected human circovirus 1 (HCirV-1) transcripts in hepatocytes and the HCirV-1 genome long-term in the patient's blood, stool, and urine. HCirV-1 is an emerging human pathogen that persists in susceptible patients.

Detection of Porcine Circovirus (PCV) Using CRISPR-Cas12a/13a Coupled with Isothermal Amplification

The impact of porcine circovirus (PCV) on the worldwide pig industry is profound, leading to notable economic losses. Early and prompt identification of PCV is essential in managing and controlling this disease effectively. A range of detection techniques for PCV have been developed and primarily divided into two categories focusing on nucleic acid or serum antibody identification. The methodologies encompass conventional polymerase chain reaction (PCR), real-time fluorescence quantitative PCR (qPCR), fluorescence in situ hybridization (FISH), loop-mediated isothermal amplification (LAMP), immunofluorescence assay (IFA), immunohistochemistry (IHC), and enzyme-linked immunosorbent assay (ELISA). Despite their efficacy, these techniques are often impeded by the necessity for substantial investment in equipment, specialized knowledge, and intricate procedural steps, which complicate their application in real-time field detections. To surmount these challenges, a sensitive, rapid, and specific PCV detection method using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas12a/13a coupled with isothermal amplification, such as enzymatic recombinase amplification (ERA), recombinase polymerase amplification (RPA), and loop-mediated isothermal amplification (LAMP), has been developed. This novel method has undergone meticulous optimization for detecting PCV types 2, 3, and 4, boasting a remarkable sensitivity to identify a single copy per microliter. The specificity of this technique is exemplary, with no observable interaction with other porcine viruses such as PEDV, PRRSV, PRV, and CSFV. Its reliability has been validated with clinical samples, where it produced a perfect alignment with qPCR findings, showcasing a 100% coincidence rate. The elegance of merging CRISPR-Cas technology with isothermal amplification assays lies in its on-site testing without the need for expensive tools or trained personnel, rendering it exceptionally suitable for on-site applications, especially in resource-constrained swine farming environments. This review assesses and compares the process and characteristics inherent in the utilization of ERA/LAMP/RPA-CRISPR-Cas12a/Cas13a methodologies for the detection of PCV, providing critical insights into their practicality and effectiveness.

Full-genome sequencing of dozens of new DNA viruses found in Spanish bat feces

Bats are natural hosts of multiple viruses, many of which have clear zoonotic potential. The search for emerging viruses has been aided by the implementation of metagenomic tools, which have also enabled the detection of unprecedented viral diversity. Currently, this search is mainly focused on RNA viruses, which are largely over-represented in databases. To compensate for this research bias, we analyzed fecal samples from 189 Spanish bats belonging to 22 different species using viral metagenomics. This allowed us to identify 52 complete or near-complete viral genomes belonging to the families Adenoviridae, Circoviridae, Genomoviridae, Papillomaviridae, Parvoviridae, Polyomaviridae and Smacoviridae. Of these, 30 could constitute new species, doubling the number of viruses currently described in Europe. These findings open the door to a more thorough analysis of bat DNA viruses and their zoonotic potential.

IMPORTANCE

Metagenomics has become a fundamental tool to characterize the global virosphere, allowing us not only to understand the existing viral diversity and its ecological implications but also to identify new and emerging viruses. RNA viruses have a higher zoonotic potential, but this risk is also present for some DNA virus families. In our study, we analyzed the DNA fraction of fecal samples from 22 Spanish bat species, identifying 52 complete or near-complete genomes of different viral families with zoonotic potential. This doubles the number of genomes currently described in Europe. Metagenomic data often produce partial genomes that can be difficult to analyze. Our work, however, has characterized a large number of complete genomes, thus facilitating their taxonomic classification and enabling different analyses to be carried out to evaluate their zoonotic potential. For example, recombination studies are relevant since this phenomenon could play a major role in cross-species transmission.

The porcine circovirus 3 humoral response: characterization of maternally derived antibodies and dynamic following experimental infection

Since Porcine Circovirus 3 (PCV3) was first identified in 2016, our understanding of the humoral response is still relatively scarce. Current knowledge of the PCV3 humoral response is primarily based on field studies identifying the seroprevalence of PCV3 Cap-induced antibodies. Studies on the humoral response following experimental PCV3 infection have conflicting results where one study reports the development of the Cap IgG response 7 days postinfection with no concurrent Cap IgM response, while a second study shows a Cap IgM response at the same time point with no detection of Cap IgG. The dynamics of the PCV3 Cap and Rep IgG following maternal antibody transfer and experimental infection have not been well characterized. Additionally, the cross-reactivity of convalescent serum from PCV2 and PCV3 experimentally infected animals to serologic methods of the alternate PCV has limited evaluation. Here, we show that maternally derived antibodies were detectable in piglet serum 7-9 weeks postfarrowing for the Cap IgG and 5-weeks-post farrowing for the Rep IgG using Cap- and Rep-specific enzyme linked immunosorbent assays (ELISA) and immunofluorescent assays (IFA) methods. Following experimental inoculation, Cap IgG was detected at 2-weeks-post inoculation and Rep IgG detection was delayed until 4-weeks-post inoculation. Furthermore, convalescent serum from either PCV2 or PCV3 methods displayed no cross-reactivity by serological methods against the other PCV. The information gained in this study highlights the development of both the Cap- and Rep-specific antibodies following experimental infection and through the transfer of maternal antibodies. The increased understanding of the dynamics of maternal antibody transfer and development of the humoral response following infection gained in the present study may aid in the establishment of husbandry practices and potential application of prophylactics to control PCV3 clinical disease.

IMPORTANCE

Research on Porcine Circovirus 3 (PCV3) immunology is vital for understanding and controlling this virus. Previous studies primarily relied on field observations, but they have shown conflicting results about the immunological response against PCV3. This study helps fill those gaps by looking at how antibodies develop in pigs, especially those maternal-derived, and their impact in neonatal pigs preventing PCV3-associated disease in piglets. In addition, we look at the dynamics of antibodies in experimental infections mimicking infection in pigs in the grower-phase condition. Understanding this process can help to develop better strategies to prevent PCV3 infection. Also, this research found that PCV2 and PCV3 do not cross-react, which is crucial for serological test development and results interpretation. Overall, this work is essential for improving swine health and farming practices in the face of PCV3 infections.

The pigeon circovirus evolution, epidemiology and interaction with the host immune system under One Loft Race rearing conditions

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.

Optimized production of full-length PCV2d virus-like particles in Escherichia coli: A cost-effective and high-yield approach for potential vaccine antigen development

Porcine circovirus type 2 (PCV2) is a globally prevalent infectious pathogen affecting swine, with its capsid protein (Cap) being the sole structural protein critical for vaccine development. Prior research has demonstrated that PCV2 Cap proteins produced in Escherichia coli (E. coli) can form virus-like particles (VLPs) in vitro, and nuclear localization signal peptides (NLS) play a pivotal role in stabilizing PCV2 VLPs. Recently, PCV2d has emerged as an important strain within the PCV2 epidemic. In this study, we systematically optimized the PCV2d Cap protein and successfully produced intact PCV2d VLPs containing NLS using E. coli. The recombinant PCV2d Cap protein was purified through affinity chromatography, yielding 7.5 mg of recombinant protein per 100 ml of bacterial culture. We augmented the conventional buffer system with various substances such as arginine, β-mercaptoethanol, glycerol, polyethylene glycol, and glutathione to promote VLP assembly. The recombinant PCV2d Cap self-assembled into VLPs approximately 20 nm in diameter, featuring uniform distribution and exceptional stability in the optimized buffer. We developed the vaccine and immunized pigs and mice, evaluating the immunogenicity of the PCV2d VLPs vaccine by measuring PCV2-IgG, IL-4, TNF-α, and IFN-γ levels, comparing them to commercial vaccines utilizing truncated PCV2 Cap antigens. The HE staining and immunohistochemical tests confirmed that the PCV2 VLPs vaccine offered robust protection. The results revealed that animals vaccinated with the PCV2d VLPs vaccine exhibited high levels of PCV2 antibodies, with TNF-α and IFN-γ levels rapidly increasing at 14 days post-immunization, which were higher than those observed in commercially available vaccines, particularly in the mouse trial. This could be due to the fact that full-length Cap proteins can assemble into more stable PCV2d VLPs in the assembling buffer. In conclusion, our produced PCV2d VLPs vaccine elicited stronger immune responses in pigs and mice compared to commercial vaccines. The PCV2d VLPs from this study serve as an excellent candidate vaccine antigen, providing insights for PCV2d vaccine research.

Development and application of a TaqMan-probe-based multiplex real-time PCR assay for simultaneous detection of porcine circovirus 2, 3, and 4 in Guangdong province of China

Porcine circoviruses disease (PCVD), caused by porcine circovirus (PCVs), is an important swine disease characterized by porcine dermatitis, nephrotic syndrome and reproductive disorders in sows. However, diseases caused by PCV2, PCV3, or PCV4 are difficult to distinguish, so a simple, rapid, accurate and high-throughput diagnostic and identification method is urgently needed to differentiate these three types. In this study, specific primers and probes were designed based on the conserved region sequences of the Rep gene of PCV2, and the Cap gene of PCV3 and PCV4. A multiplex qPCR assay was developed and optimized that the limit of detection concentration could reach as low as 3.8 copies/μL, with all correlation coefficients (R2) exceeding 0.999. Furthermore, the method showed no cross-reaction with other crucial porcine viral pathogens, and both intra-repeatability and inter-reproducibility coefficients of variation were below 2%. The assay was applied to the detection of 738 pig samples collected from 2020 to 2021 in Guangdong Province, China. This revealed positive infection rates of 65.18% for PCV2, 29.27% for PCV3, and 0% for PCV4, with a PCV2/PCV3 co-infection rate of 23.17%. Subsequently, complete genome sequences of 17 PCV2 and 4 PCV3 strains were obtained from the above positive samples and pre-preserved positive circovirus samples. Nucleotide sequence analysis revealed that the 17 PCV2 strains shared 96.7-100% complete nucleotide identity, with 6 strains being PCV2b and 11 strains being PCV2d; the 4 PCV3 strains shared 98.9-99.4% complete nucleotide identity, with 2 strains being PCV3a-1 and 2 strains being PCV3b. This research provides a reliable tool for rapid PCVs identification and detection. Molecular epidemiological investigation of PCVs in pigs in Guangdong Province will help us to understand PCV2 and PCV3 epidemiological characteristics and evolutionary trends.

Circular Single-Stranded DNA: Discovery, Biological Effects, and Applications

The field of nucleic acid therapeutics has witnessed a significant surge in recent times, as evidenced by the increasing number of approved genetic drugs. However, current platform technologies containing plasmids, lipid nanoparticle-mRNAs, and adeno-associated virus vectors encounter various limitations and challenges. Thus, we are devoted to finding a novel nucleic acid vector and have directed our efforts toward investigating circular single-stranded DNA (CssDNA), an ancient form of nucleic acid. CssDNAs are ubiquitous, but generally ignored. Accumulating evidence suggests that CssDNAs possess exceptional properties as nucleic acid vectors, exhibiting great potential for clinical applications in genetic disorders, gene editing, and immune cell therapy. Here, we comprehensively review the discovery and biological effects of CssDNAs as well as their applications in the field of biomedical research for the first time. Undoubtedly, as an ancient form of DNA, CssDNA holds immense potential and promises novel insights for biomedical research.

DUSP1 mRNA modulation during porcine circovirus type 2 and porcine reproductive and respiratory syndrome virus co-infection regulates viruses replication

The effects of porcine circovirus type 2b (PCV2b) and porcine reproductive and respiratory syndrome virus (PRRSV) co-infection in epithelial cells of the swine respiratory tract is unknown. In the present study, the newborn pig trachea cell line NPTr-CD163, which is permissive to both viruses, was persistently infected with PCV2b and then with PRRSV. Viral replication, cell viability, cytokines' mRNA expression, and modulation of cellular genes expression were evaluated in infected cells. In NPTr-CD163 co-infection model, PCV2b replication was enhanced while PRRSV replication was suppressed. Cell viability was significantly decreased during PCV2b single infection and co-infection compared to mock-infected and PRRSV single infected cells. However, no difference was observed in cell viability between PCV2b and PCV2b/PRRSV infected cells. The IL6, IL8 and IL10 mRNA expression was significantly higher in co-infected cells compared to PCV2b and PRRSV single infected cells. Moreover, the IFN-α/β expression was significantly reduced in co-infected cells compared to PCV2b infected cells whereas it remained higher compared to PRRSV infected cells. The differential gene expression analysis revealed that the mRNA expression level of the cellular gene DUSP1 was significantly higher in all PRRSV infection models compared to PCV2b single infected cells. Knockdown of DUSP1 expression in co-infected cells significantly reduced PCV2b replication, suggesting a role for DUSP1 in PCV2b/PRRSV pathogenesis.

Nucleophosmin 1a translocated from nucleus to cytoplasm and facilitate GCRV replication

To decipher the functional characterization of Nucleophosmin 1a (NPM1a) from grass carp (Ctenopharyngodon idellus) (CiNPM1a), its cDNA was cloned and bioinformatic analysis were conducted. The full-length cDNA sequence of CiNPM1a is 1732 bp, which encodes 307 amino acids. CiNPM1a contains conserved domains of Nucleoplasmin domain, NPM1-C terminal domain, as well as nuclear localization signals, nuclear export signal (NES) and acid patches. There are 52 and 20 consensus amino acids exist in the Nucleoplasmin domain and the NPM1-C terminal domain of all blasted species. In addition, the immune function of CiNPM1a were analyzed. The Ciirf7, Ciifn1 and Ciifn2 transcription was inhibited, whereas the vp2 and vp7 expressions were enhanced in CiNPM1a overexpressing cells after GCRV infection (P < 0.05). Moreover, the Ciirf7, Ciifn1 and Ciifn2 mRNA levels were significantly up-regulated, but the vp2 and vp7 expressions were significantly down-regulated in CiNPM1a knockdown cells after infection. This indicated that CiNPM1a played negative roles in the induction of Type I IFN reaction and thus the GCRV replication. Finally, the NES domain that affect the nucleous-cytoplasm shuttle and the replication of GCRV were investigated. The deletion of NES1 and NES(1 + 2+3) absolutely limited the transloacation of CiNPM1a△NES1 protein and CiNPM1a △NES(1 + 2+3) protein to cytoplasm after infection, and the deletion of NES2 resulted in partially limitation of protein shuttle. In general, Ciirf3, Ciirf7, Ciifn1 and Ciifn2 expressions were enhanced in the CiNPM1a△NES1, CiNPM1a△NES2 and CiNPM1a△NES3 overexpression groups, and the deletion of functional domains in CiNPM1a led to significantly reduction of the vp2 and vp7 replication. The results indicated that CiNPM1a may be a target molecular for GCRV infection curation, and a candidate molecular for resistance strain breeding of grass carp.

Novel Circovirus in Blood from Intravenous Drug Users, Yunnan, China

We identified a novel circovirus (human-associated circovirus 2 [HuCV2]) from the blood of 2 intravenous drug users in China who were infected with HIV-1, hepatitis C virus, or both. HuCV2 is most closely related to porcine circovirus 3. Our findings underscore the risk for HuCV2 and other emerging viruses among this population.

Phylogenetic and Structural Analysis of Porcine Circovirus Type 2 from 2016 to 2021 in Jilin Province, China

Porcine circovirus disease (PCVD) caused by porcine circovirus type 2 (PCV2) is widely distributed in pig farms. Up until now, nine genotypes of PCV2, PCV2a to 2i, have been identified in diseased pigs worldwide. This study analyzed 302 samples collected in the Jilin Province of China from 2016 to 2021, followed by genetic analysis of the PCV2 isolates. Meanwhile, the antigen epitopes, amino acid mutations, 3D structure of the PCV2 isolates and commercially available vaccine strains were evaluated and compared. The results showed that the predominant genotypes of PCV2 were PCV2b, followed by PCV2e and PCV2d in Jilin Province during 2016-2021. Although mutations were detected in the isolates, no recombination occurred in the PCV2 isolates, indicating a stable genotype of PCV2 in Jilin Province during these years. Moreover, the B cell epitopes in the Cap and Rep proteins of eighteen PCV2 isolates and T cell epitopes in the Cap of the isolates were changed compared to three currently used vaccine strains. The mutations in the Cap and Rep proteins did not affect their spatial conformation. Therefore, bivalent or multivalent vaccines with different genotypes of PCV2 might improve the protective effect of vaccines.

Special Issue "State-of-the-Art Porcine Virus Research in China"

China is one of the major countries involved in pig production and pork consumption [...].

Flavonoids as Potential Antiviral Agents for Porcine Viruses

Flavonoids are types of natural substances with phenolic structures isolated from a variety of plants. Flavonoids have antioxidant, anti-inflammatory, anticancer, and antiviral activities. Although most of the research or applications of flavonoids are focused on human diseases, flavonoids also show potential applicability against porcine virus infection. This review focuses on the recent progress in antiviral mechanisms of potential flavonoids against the most common porcine viruses. The mechanism discussed in this paper may provide a theoretical basis for drug screening and application of natural flavonoid compounds and flavonoid-containing herbs to control porcine virus infection and guide the research and development of pig feed additives.

Porcine circovirus type 2 induces CHOP-ERO1α-ROS-mediated apoptosis in PK-15 cells

Porcine circovirus type 2 (PCV2) infection induces endoplasmic reticulum (ER) stress and oxidative stress. These cellular responses could be connected with apoptosis. However, the mechanisms that link ER stress and oxidative stress in PCV2-induced apoptosis are poorly characterized. Here, we demonstrate that PCV2 infection increased expression of proapoptotic protein C/EBP homologous protein (CHOP) and ER oxidoreductase 1 alpha (ERO1α). Inhibition of CHOP by RNA silencing or inhibition of ERO1α by short hairpin RNA or EN460 repressed PCV2-induced reactive oxygen species (ROS) generation, cytosolic calcium level, and apoptotic rate in PK-15 cells. Overexpression of ERO1α enhanced PCV2-induced oxidative stress, caspase-3 cleavage, and apoptosis rate. Treatment of PCV2-infected cells with ROS scavenger N-acetyl-L-cysteine downregulated PCV2-induced ROS production, cytosolic calcium level, and apoptosis rate, but intriguingly decreased expression of CHOP and ERO1α. Thus, we propose that PCV2 induces apoptosis through ER Stress via CHOP-ERO1α-ROS signaling in host cells.