Porcine circovirus type 2 in China: an update on and insights to its prevalence and control

A novel linear B cell epitope of the porcine circovirus type 3 capsid protein identified by phage display technology

Porcine circovirus type 3 (PCV3) is endemic in swine worldwide and causes reproductive disorders, dermatitis and nephrotic syndrome, and multi-organ inflammation. PCV3 capsid protein (Cap) can self-assemble into virus-like particles (VLPs), and is an ideal candidate for vaccines and diagnostic reagents.In this study, the recombinant PCV3 Cap protein was successfully expressed in E. coli by deleting the nuclear localization sequence (NLS). The PCV3 VLPs were observed by transmission electron microscopy, and its immunogenicity was evaluated in six-week-old female BALB/c mice. A monoclonal antibody was named mAb 2D6, and demonstrated strong reactivity and specificity to PCV3 Cap. The purified mAb 2D6 was further used for bio-panning to select phage expressing specific epitopes from phage-displayed 7 mer-peptide library. A novel linear B-cell epitope, recognized by mAb 2D6, was identified at the amino acid region 47-53 of Cap. The phage peptide sequences were analyzed using multiple sequence alignment and evaluated by peptide ELISA. These results provide insights for developing diagnostic tools and potential vaccines for PCV3.

Detection of PCV2d in Vaccinated Pigs in Colombia and Prediction of Vaccine T Cell Epitope Coverage against Circulating Strains Using EpiCC Analysis

Porcine circovirus type 2 (PCV2) is strongly linked to a group of syndromes referred to as porcine-circovirus-associated diseases (PCVADs), which are controlled through vaccination; however, this does not induce sterilizing immunity but is instead involved in the evolution of the virus and is considered a factor in vaccine failure. This study sampled 84 herds (167 pigs) vaccinated against PCV2 and with clinical signs of PCVADs in five provinces across Colombia. PCV2 was identified and further characterized at the molecular level via genotyping and phylogenetic reconstructions. In addition, PCV2-associated lesions were examined via histopathology. Furthermore, the PCV2-Cap sequences retrieved were compared with three vaccines via the EpiCC tool and T cell epitope coverage. The prevalence of PCV2 was 82% in pigs and 92.9% in herds. The highest viral loads were identified in lymphoid tissue, and PCV2d emerged as the most predominant in pigs and herds (93.4% and 92.3%). Sequences for PCV2-ORF2 (n = 57; 55 PCV2d and 2 PCV2a) were determined, and PCV2d sequences were highly similar. The most common pneumonia pattern was suppurative bronchopneumonia, while the most common lung lesion was exudation in the airways; in lymphoid tissue, there was lymphoid depletion. The bivalent vaccine (PCV2a and PCVb) exhibited a higher EpiCC score (8.36) and T cell epitope coverage (80.6%) than monovalent PCV2a vaccines. In conclusion, PCV2d currently circulates widely in Colombia. Despite vaccination, there are clinical cases of PCV2, and immunoinformatic analyses demonstrate that bivalent vaccines improved the average coverage.

Establishment and preliminary application of duplex fluorescence quantitative PCR for porcine circoviruses type 2 and type 3

Porcine circovirus types 2 (PCV2) and 3 (PCV3) are the two most prevalent porcine circoviruses in China, all of which can infect swine herds and cause serious diseases. To detect coinfection with PCV2 and PCV3, primers and probes for duplex PCV2 and PCV3 real-time PCR were designed to target their cap genes based on the constructed plasmids pUC57-PCV2 and pUC57-PCV3. The established duplex PCV2 and PCV3 real-time PCRs were specific to PCV2 and PCV3 and showed no cross-reactions with other porcine viral pathogens. The limit of detection was 5 and 50 copies for the PCV2 and PCV3 plasmids, respectively. The intra- and interassay repeatability had coefficients of variation below 3 %. The established methods were used to analyze clinical samples from Liaoning and Jilin provinces of China. The coinfection rates of PCV2 and PCV3 in pigs extensively fed in Liaoning and Jilin, large-scale farmed pigs in Liaoning and large-scale farmed pigs in Jilin were 15.0 % (6/40), 36.7 % (11/30) and 35.4 % (62/175), respectively. This study established a useful duplex PCV2 and PCV3 real-time PCR method that can be used for the detection of PCV2 and PCV3 in local clinical samples.

Molecular analysis of canine circovirus in dogs from animal shelters in Belém, Pará, northern Brazil: first detection at the amazon region

The canine circovirus (CanCV) is a single-stranded DNA virus that has become an important emerging virus associated with gastroenteritis in dogs worldwide. In the present study, the CanCV was detected by PCR in 15% (22/147) of dogs from animal shelters in Belém, between 2019 and 2020. We observed an association between the CanCV infection and the presence of diarrhea in animals younger than one year of age (p > 0.01). The Brazilian strains were grouped in Chinese genotypes, with 99.54 to 100% nucleotilde homology. The GMRF Bayesian Skyride used the molecular clock model, which was the best suited technique to plot the dataset. The most recent common ancestor (TMRCA) was estimated in 2017, with the evolution rate of 1.6 x 10-3 s/s/y. The viral family diversity was also investigated, with emphasis on the families of the enteric pathogenic viruses Parvoviridae, Picornaviridae and Astroviridae, which were detected in the CanCV positive pooled samples. This study highlights the importance of the CanCV as an emergent virus that causes diarrhea in Brazilian dogs. The results found herein contribute to the understanding of the role of CanCV in enteric diseases and in the evolutionary molecular characterization of the circulating genotypes. Furthermore, we increased the understanding of the fecal virome in dogs with diarrhea, providing data for the monitoring and prevention viral gastroenteric diseases in domestic animals.

Porcine circovirus type 2 infection inhibits macrophage M1 polarization induced by other pathogens via viral capsid protein and host gC1qR protein

Porcine circovirus type 2 (PCV2) has been proven to co-infect with a variety of pathogens and cause immunosuppression. Previously, we have reported that PCV2 infection attenuates the production of pro-inflammatory cytokines induced by other pathogens in porcine macrophages. However, whether PCV2 can affect M1-type macrophage polarization induced by other pathogens is less well reported. Herein, we found that PCV2 infection suppressed M1 macrophage production induced by porcine reproductive and respiratory syndrome virus (PRRSV) and Haemophilus parasuis (H. parasuis) in the lung and promoted the proliferation of these pathogens in the piglets. Consistently, we confirmed that PCV2 inhibits M1 macrophage production and its associated gene expression in porcine alveolar macrophages (PAMs) both ex vivo and in vitro. Meanwhile, PCV2 inhibited lipopolysaccharide (LPS)-induced pro-inflammatory cytokines in vitro in a time- and dose-dependent manner. In PCV2-infected cells, LPS-induced signal transducer and activator of transcription (STAT1) phosphorylation and its nuclear translocation were decreased. Based on these findings, we further identified a role for PCV2 capsid protein (Cap) in LPS-induced M1 macrophage-associated genes and found that PCV2 Cap can significantly reduce STAT1 phosphorylation and its nuclear translocation, as well as the production of M1 macrophage-related genes. As the binding protein of PCV2 Cap, gC1qR protein was also associated with this inhibition process. gC1qR-binding activity-deficient PCV2 Cap mutated protein (Cap RmA) appeared an attenuated inhibitory effect on other pathogen-induced polarization of M1-type macrophages, suggesting that the inhibitory effect of PCV2 infection on M1-type macrophage polarization induced by other pathogens is dependent on Cap protein and the host gC1qR protein. Altogether, our results demonstrate that PCV2 infection inhibits macrophage M1 polarization induced by other pathogens via capsid and host gC1qR protein modulating JAK/STAT signaling.

Epizootiological surveillance of porcine circoviruses in free-ranging wild boars in China

Four species of porcine circoviruses (PCV1-4) have been reported to circulate in Chinese domestic pigs, while the epizootiology of these viruses in free-ranging wild boars in China remains unknown. In this study, tissue and serum samples collected from diseased or apparently healthy wild boars between 2018 and 2020 in 19 regions of China were tested for the prevalence of PCV1-4 infections. Positive rates of PCV1, PCV2, and PCV3 DNA in the tissue samples of Chinese wild boars were 1.6% (4/247), 58.3% (144/247), and 10.9% (27/247) respectively, with none positive for PCV4. Sequence analysis of viral genome showed that the four PCV1 strains distributed in Hunan and Inner Mongolia shared 97.5%-99.6% sequence identity with global distributed reference strains. Comparison of the ORF2 gene sequences showed that 80 PCV2 strains widely distributed in 18 regions shared 79.5%-100% sequence identity with reference strains from domestic pigs and wild boars, and were grouped into PCV2a (7), PCV2b (31) and PCV2d (42). For PCV3, 17 sequenced strains shared 97.2%-100% nucleotide identity at the genomic level and could be divided into PCV3a (3), PCV3b (2) and PCV3c (12) based on the phylogeny of ORF2 gene sequences. Serological data revealed antibody positive rates against PCV1 and PCV2 of 11.4% (19/167) and 53.9% (90/167) respectively. The data obtained in this study improved our understanding about the epidemiological situations of PCVs infection in free-ranging wild boars in China and will be valuable for the prevention and control of diseases caused by PCVs infection.

Development of a Gold Nanoparticle-Based Immunochromatographic Strip for Rapid Detection of Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is an important swine infectious pathogen that seriously threatens the global swine industry. PCV2 Cap protein is the only structural and the main immunogenic protein constituting the viral capsid. In this study, a gold nanoparticle-based immunochromatographic strip with high sensitivity and specificity was developed which could be used for rapid detection of PCV2 virions or Cap protein in research. The visual detection limit of the strip was 103.18 50% tissue culture infective does (TCID50)/mL for PCV2, and 2.03 μg/mL for PCV2 Cap protein. No cross-reactivity was observed with the PCV1 and PCV3 Cap proteins and other common swine pathogens such as porcine reproductive and respiratory syndrome virus, classical swine fever virus, pseudorabies virus, porcine epidemic diarrhea virus, porcine parvovirus, and swine influenza virus. The repeatability of the strip was good. The stability of the strip was perfect for 12 months in a dry state at room temperature. Visual results could be obtained within 5 min by simply inserting the strip into the diluted sample. The strip is a time-saving, labor-saving, and reliable tool for testing of PCV2 virions or Cap protein in research. The idea of this study might open a new perspective for the application of the strip. IMPORTANCE Porcine circovirus type 2 (PCV2) Cap protein is the only structural and the main immunogenic protein constituting the viral capsid. Although many methods can be used to identify PCV2 or PCV2 Cap protein in vaccine research, they usually require high workload and time. The developed strip can specifically detect PCV2 virions or Cap protein, and visual qualitative results can be obtained within 5 min by simply diluting the sample and inserting the strip into the sample. The final value of the strip is providing a simple and time-saving method for real-time monitoring of PCV2 antigen in vaccine research with reliable results, such as the different stages of PCV2 Cap protein expression and purification, as well as the different stages of PCV2 reproduction and purification.

Matrine combined with Osthole inhibited the PERK apoptosis of splenic lymphocytes in PCV2-infected mice model

BACKGROUND

Porcine circovirus type 2 (PCV2) is one of the major pathogens commonly found in pigs, which causes immunosuppression and apoptosis. Vaccination and a single drug cannot totally prevent and treat PCV2 infection. Our previous in vitro study reported that the synergistic anti-PCV2 effect of Matrine and Osthole was better than that of Matrine or Osthole alone, This study was aimed to evaluate the synergistic anti-PCV2 effect as well as the underline molecular mechanism of Matrine and Osthole in Kunming (KM) mice model infected with PCV2. KM mice were randomly divided into 8 groups namely control group, PCV2 infected, Matrine combined with Osthole high dose treatment (40 mg/kg + 12 mg/kg), medium dose treatment (20 mg/kg + 6 mg/kg), low dose treatment (10 mg/kg + 3 mg/kg), Matrine treatment (40 mg/kg), Osthole treatment (12 mg/kg) and Ribavirin positive control (40 mg/kg) groups. PCV2 was intraperitoneally (i.p.) injected in all mice except the control group. 5 days of post-infection (dpi), mice in different treatment groups were injected i.p. with various doses of Matrine, Osthole and Ribavirin once daily for the next 5 consecutive days.

RESULTS

The synergistic inhibitory effect of Matrine and Osthole on PCV2 replication in mouse liver was significantly heigher than that of Matrine and Osthole alone. The expression of GRP78, p-PERK, p-eIF2α, ATF4, CHOP, cleaved caspase-3 and Bax proteins were significantly reduced, while that of Bcl-2 was significantly increased in Matrine combined with Osthole groups, which alleviated the pathological changes caused by PCV2, such as interstitial pneumonia, loss of spleen lymphocytes, infiltration of macrophages and eosinophils.

CONCLUSIONS

The synergistic anti-apoptotic effect of Matrine and Osthole was better than their alone effect, Both Matrine and Osthole had directly inhibited the expression of PCV2 Cap and the apoptosis of spleen cells induced by PCV2 Cap through the PERK pathway activated by endoplasmic reticulum (ER) GRP78. These results provided a new insight to control PCV2 infection and provide good component prescription candidate for the development of novel anti-PCV2 drugs.

Evolutionary Origin, Genetic Recombination, and Phylogeography of Porcine Kobuvirus

The newly identified porcine Kobuvirus (PKV) has raised concerns owing to its association with diarrheal symptom in pigs worldwide. The process involving the emergence and global spread of PKV remains largely unknown. Here, the origin, genetic diversity, and geographic distribution of PKV were determined based on the available PKV sequence information. PKV might be derived from the rabbit Kobuvirus and sheep were an important intermediate host. The most recent ancestor of PKV could be traced back to 1975. Two major clades are identified, PKVa and PKVb, and recombination events increase PKV genetic diversity. Cross-species transmission of PKV might be linked to interspecies conserved amino acids at 13-17 and 25-40 residue motifs of Kobuvirus VP1 proteins. Phylogeographic analysis showed that Spain was the most likely location of PKV origin, which then spread to pig-rearing countries in Asia, Africa, and Europe. Within China, the Hubei province was identified as a primary hub of PKV, transmitting to the east, southwest, and northeast regions of the country. Taken together, our findings have important implications for understanding the evolutionary origin, genetic recombination, and geographic distribution of PKV thereby facilitating the design of preventive and containment measures to combat PKV infection.

Canine circovirus: An emerging or an endemic undiagnosed enteritis virus?

Canine Circovirus (CanineCV) belongs to the family Circoviridae. It is an emerging virus described for the first time in 2011; since then, it has been detected in different countries and can be defined as worldwide distribution virus. CanineCV infects domestic and wild canids and is mainly related to hemorrhagic enteritis in canines. However, it has been identified in fecal samples from apparently healthy animals, where in most cases it is found in coinfection with other viral agents such as the canine parvovirus type-2 (CPV). The estimated prevalence/frequency of CanineCV has been variable in the populations and countries where it has been evaluated, reaching from 1 to 30%, and there are still many concepts to define the epidemiological characteristics of the virus. The molecular characterization and phylo-evolutive analyses that allow to postulate the wild origin and intercontinental distribution of the virus. This review focuses on the importance on continuing research and establish surveillance systems for this emerging virus.

Visual and label-free ASFV and PCV2 detection by CRISPR-Cas12a combined with G-quadruplex

African swine fever (ASF) and postweaning multisystemic wasting syndrome (PMWS) are acute infectious diseases caused by the African swine fever virus (ASFV) and porcine circovirus type 2 (PCV2). At present, there are no effective vaccines for the prevention of ASFV. PMWS, which is harmful to the domestic and even the world pig industry, is difficult to cure and has a high mortality. So, developing simple, inexpensive, and accurate analytical methods to detect and effectively diagnose ASFV and PCV2 can be conducive to avoid ASFV and PCV2 infection. CRISPR has become a potentially rapid diagnostic tool due to recent discoveries of the trans-cleavage properties of CRISPR type V effectors. Herein, we report the visual detection based on CRISPR-Cas12a (cpf1), which is more convenient than fluorescence detection. Through in vitro cleavage target DNA activation, Cas12a can trans-cleavage ssDNA G-quadruplex. TMB/H2O2 and Hemin cannot be catalyzed by cleavaged G-DNA to produce green color products. This protocol is useful for the detection of ASFV and PCV2 with high sensitivity. This method can enable the development of visual and label-free ASFV and PCV2 detection and can be carried out in the field without relying on instruments or power. This method can complete nucleic acid detection at 37 °C without using other instruments or energy. Our research has expanded the application of Cas12a and laid the foundation for the field's rapid detection of viral nucleic acid in future.

First Identification and Phylogenetic Analysis of Porcine Circovirus Type 4 in Fur Animals in Hebei, China

A novel circovirus called porcine circovirus type 4 (PCV4) was recently detected in pigs suffering from severe clinical diseases in Hunan province, China. There are few reports on the origin and evolution of PCV4, although some researchers have conducted epidemiological investigations of PCV4 and found that PCV4 is widespread in pigs. Based on the previous study, we detected PCV2 in farmed foxes and raccoon dogs with reproductive failure. To explore whether the PCV4 genome also exists in fur animals, we detected 137 cases admitted from fur animal farms in Hebei China between 2015 and 2020, which were characterized by inappetence, lethargy, depression, abortion, and sterility. The overall infection rate of PCV4 was 23.36% (32/137), including 20.37% (22/108) for raccoon dogs, 18.75% (3/16) for foxes, and 53.85% (7/13) for minks. Finally, five raccoon dog-origin PCV4 strains and one fox-origin PCV4 strain were sequenced in our study, whose nucleotide identities with other representative PCV4 strains varied from 96.5% to 100%. Phylogenetic analysis based on the complete genomes of PCV4 strains indicated a close relationship with those of PCV4 strains identified from pigs. To our knowledge, this is the first study to detect PCV4 in fur animals. Interestingly, we also identified PCV4 in a mixed farm (feeding pigs and raccoon dogs at the same time). In summary, our findings extend the understanding of the molecular epidemiology of PCV4 and provide new evidence for its cross-species transmission.

Viromic analysis of feces from laboratory rabbits reveals a new Circovirus

BACKGROUND

Members of the genus Circovirus with the family Circoviridae are responsible for fatal diseases that can affect mammals and birds. Beak and feather disease virus (BFDV) is responsible for fatal diseases that could affect birds, causing the psittacine beak and feather disease. The current study discovered a new Circovirus from feces of laboratory rabbits and name it RabCV, which shows close relationship to BFDVs.

RESULTS

We investigated the feces virome of 10 laboratory rabbits using the viral metagenomic method. In these samples, we detected a new rabbit-associated Circovirus (RabCV) and performed phylogenetic analysis based on replication-associated (Rep) protein. The result showed that the RabCV was closely clustered with BFDVs, sharing the identity of 56.7%-57.2% with them based on the whole genome sequence. PCR screening in a cohort of 38 laboratory rabbits showed that 3 out of the 38 rabbits were positive for this new rabbit-associated Circovirus.

CONCLUSION

A new Circovirus was discovered from feces of rabbits, which showed low prevalence in the healthy laboratory rabbits. BFDV is responsible for fatal diseases that could affect birds, which suggested that the potential threat of the new rabbit-associated Circovirus to the health of laboratory rabbits needs further study.

Immunoglobin G Sero-Dynamics Aided Host Specific Linear Epitope Identification and Differentiation of Infected from Vaccinated Hosts

Differentiation of infected from vaccinated hosts (DIVH) is a critical step in virus eradication programs. DIVH-compatible vaccines, however, take years to develop, and are therefore unavailable for fighting the sudden outbreaks that typically drive pandemics. Here, we establish a protocol for the swift and efficient development of DIVH assays, and show that this approach is compatible with any type of vaccines. Using porcine circovirus 2 (PCV2) as the experimental model, the first step is to use Immunoglobin G (IgG) sero-dynamics (IsD) curves to aid epitope discovery (IsDAED): PCV2 Cap peptides were categorized into three types: null interaction, nonspecific interaction (NSI), and specific interaction (SI). We subsequently compared IsDAED approach and traditional approach, and demonstrated identifying SI peptides and excluding NSI peptides supports efficient diagnostic kit development, specifically using a protein-peptide hybrid microarray (PPHM). IsDAED directed the design of a DIVH protocol for three types of PCV2 vaccines (while using a single PPHM). Finally, the DIVH protocol successfully differentiated infected pigs from vaccinated pigs at five farms. This IsDAED approach is almost certainly extendable to other viruses and host species. IMPORTANCE Sudden outbreaks of pandemics caused by virus, such as SARS-CoV-2, has been determined as a public health emergency of international concern. However, the development of a DIVH-compatible vaccine is time-consuming and full of uncertainty, which is unsuitable for an emergent situation like the ongoing COVID-19 pandemic. Along with the development and public health implementation of new vaccines to prevent human diseases, e.g., human papillomavirus vaccines for cervical cancer; enterovirus 71 vaccines for hand, foot, and mouth disease; and most recently SARS-CoV-2, there is an increasing demand for DIVH. Here, we use the IsDAED approach to confirm SI peptides and to exclude NSI peptides, finally to direct the design of a DIVH protocol. It is plausible that our IsDAED approach is applicable for other infectious disease.

Production of Bivalent Subunit Vaccine for Porcine via 2A-Like Sequence in Baculovirus Expression Vector System

Classical swine fever virus (CSFV) and porcine circovirus type 2 (PCV2) have caused severe diseases in swine populations worldwide. Here, a polycistronic baculovirus vector was developed to express a bivalent vaccine, consisting of the CSFV-E2 and PCV2-Cap protein, and an immunomodulator protein derived from the Flammulina velutipes, FVE-FIP, as well as the selection marker, green fluorescent protein. The simultaneous expression of the CSFV-E2 and PCV2-Cap protein was mediated by the 2A-like sequence derived from the Perina nuda virus (PnV), while the expression of the FVE-FIP was driven by the internal ribosome entry site (IRES) element derived from the Rhophalosipum padi virus (RhPV). The Western blot analysis result suggested that the CSFV-E2, PCV2-Cap, and FVE-FIP protein were successfully co-expressed by the infected Spodoptera frugiperda IPBL-Sf21 (Sf21) cell line. The extracted cell lysate containing all three recombinant proteins was administered to Balb/C mice with or without the supplementation of Freund’s adjuvant. The ELISA analysis of the serum collected from all the immunized groups showed detectable antibodies against CSFV-E2 and PCV2-Cap. Furthermore, the immunized group without the adjuvant supplementation demonstrated a similar level of antibodies to the group with adjuvant supplementation, suggesting the efficiency of the FVE-FIP in enhancing the immune response. These results demonstrated the polycistronic baculovirus vector could be employed to develop bivalent vaccines for pigs.

A Novel Virus-Like Agent Originated From Genome Rearrangement of Porcine Circovirus Type 2 (PCV2) Enhances PCV2 Replication and Regulates Intracellular Redox Status In Vitro

Genome rearrangement occurs to porcine circovirus type 2 (PCV2) during in vitro and in vivo infections, and a number of rearranged PCV2 genomes have been isolated and characterized. This study was conducted to investigate the role of the rearranged PCV2 (rPCV2) in PCV2 replication and the biological effect of rPCV2 in host cells. Two whole rPCV2 genome sequences (358 nt and 1125 nt in length) were synthesized and recombinant plasmids pBSK(+)-rPCV2 (pBSK(+)-1125 and pBSK(+)-358) were constructed. A novel virus-like agent (rPCV2-1125) was rescued by in vitro transfection of porcine kidney cell line (PK-15) and porcine alveolar macrophage 3D4/21 cells. The data indicate that rPCV2-1125 significantly enhanced PCV2 replication in vitro. Furthermore, rPCV2-1125 led to oxidative stress in host cells, as indicated by decreased intracellular glutathione (GSH) and total superoxide dismutase (SOD) activities, as well as increased malondialdehyde (MDA) levels. These results provide new insights into genome rearrangement of PCV2 and will contribute to future studies of PCV2 replication and associated mechanisms.

Molecular Epidemic Characteristics and Genetic Evolution of Porcine Circovirus Type 2 (PCV2) in Swine Herds of Shanghai, China

Porcine Circovirus 2 (PCV2) is a crucial swine pathogen and considered a primary causative agent of porcine circovirus-associated diseases (PCVADs), posing a serious economic threat to the swine industry across globe. The world’s biggest agricultural conglomerates have teamed up to create giant commercial pig farms across Shanghai due to the proximity of this region to more affluent lean-pork markets. Since its discovery, PCV2 has displayed extraordinary genetic diversity, and its genome is swiftly evolving through a series of mutations and recombinations. However, limited information on epidemiology, molecular characteristics, vaccine cross-protection, and the co-infection rate of PCV2 with other lethal swine diseases can adversely impact the pig production in the region. To investigate the molecular epidemic characteristics and genetic evolution of PCV2, pigs with doubtful symptoms of PCVADs were sampled from various commercial pig farms with a history of PWMS and/or PDNS across Shanghai from 2014 to 2018. Our results revealed the coexistence of multiple PCV2 genotypes (PCV2b, PCV2e, and PCV2d) among Shanghai pig herds and dominance of PCV2d among them. We also found critical amino acid substitutions in epitope regions of important capsid proteins in PCV2 isolates involved in viral replication and host immune escape. Spotted mutations may favor the prevalence and survival of various PCV2 genotypes despite availability of commercial vaccines. This study also provides insight into the co-infection status of PCV2 with major lethal swine viral diseases such as PPV and PPRSV. Collectively, these investigations will contribute to understanding the molecular epidemiology and evolution of PCV2 across the region.

Detection and genetic characteristics of porcine circovirus type 2 and 3 in Henan province of China

PCV2 is one of the most economically important viral agents in swine worldwide. Recently, PCV3 has been frequently reported, and the co-infection of PCV2 and PCV3 is common in China. In order to explore the distribution, epidemiology and genetic diversity of PCV2 and PCV3, a total of 1,760 clinical tissue samples were randomly collected from 18 different regions in Henan province of China from October 2018 to September 2019 and screened for the presence of PCV2 and PCV3 by a duplex real-time PCR assay. The results showed that the positive rates of PCV2 and PCV3 were 72.90% and 5.17% respectively, and the co-infection rate of the two viruses was 3.64%. PCV2 and PCV3 are prevalent all year round. The prevalence of PCV2 in diseased pigs was 83.98%, higher than that in slaughterhouse pigs, while the prevalence of PCV3 in diseased pigs was 2.16%, slightly lower than that in slaughterhouse pigs. Furthermore, the complete genomes of 14 PCV2 and 3 PCV3 strains were obtained, among which 1 belonged to PCV2a, 5 belonged to PCV2b and 8 belonged to PCV2d. A new variant strain (XX2) might escape the host immune system. The phylogenetic analysis of PCV3 showed high nucleotide identity (>98%) between sequences obtained in this study and reference sequences. The results of this study might enrich the epidemiological data of PCV2 and PCV3 in Henan province and provide reference information for the comprehensive prevention and control of PCVAD.

Update of Genetic Diversity of Porcine Circovirus Type 2 in Chile Evidences the Emergence of PCV2d Genotype

Porcine Circovirus 2 (PCV2) can cause multiple clinical conditions known as porcine circovirus-associated diseases (PCVAD). Before the wide availability of PCV2 vaccines, PCVAD resulted in significant losses to the global swine industry. PCV2's rapid evolutionary dynamics are comparable to single-stranded RNA viruses. Thus, shifts in the dominance and distribution of different genotypes may frequently occur, resulting in the emergence and spread of varying PCV2 genotypes and recombinant strains in swine. This study aims at identifying the PCV2 genotypes currently circulating in Chile. Seven hundred thirty-eight samples were obtained from 21 swine farms between 2020 and 2021. The samples were tested using PCR for species detection and genotyping. Sequencing and phylogenetic analyses were conducted in selected samples. PCV2 was detected in 26.9% of the PCR reactions and 67% of the sampled farms. The genotypes were determined in nine farms, PCV2a in one farm, PCV2b in four, and PCV2d in five, with PCV2b and PCV2d co-circulating in one farm. The phylogenetic analysis of twelve ORF2 sequences obtained (PCV2a = 5; PCV2b = 4; PCV2d = 3) showed a PCV2a Chilean strains monophyletic cluster; closely related to Chilean viruses collected in 2012 and 2013. Of the three different PCV2b sequenced viruses, two viruses were close to the root of the PCV2b group, whereas the remaining one grouped with a South Korean virus. PCV2d sequences were closely related to Asian viruses. A previously reported PCV2a/PCV2d recombinant strain was not detected in this study. Our results suggest the emergence and potential shift to PCV2d genotype in Chilean farms.

Comprehensive Analysis of Codon Usage Patterns in Chinese Porcine Circoviruses Based on Their Major Protein-Coding Sequences

Porcine circoviruses (PCVs) are distributed in swine herds worldwide and represent a threat to the health of domestic pigs and the profits of the swine industry. Currently, four PCV species, including PCV-1, PCV-2, PCV-3 and PCV-4, have been identified in China. Considering the ubiquitous characteristic of PCVs, the new emerged PCV-4 and the large scale of swine breeding in China, an overall analysis on codon usage bias for Chinese PCV sequences was performed by using the major proteins coding sequences (ORF1 and ORF2) to better understand the relationship of these viruses with their host. The data from genome nucleotide frequency composition and relative synonymous codon usage (RSCU) analysis revealed an overrepresentation of AT pair and the existence of a certain codon usage bias in all PCVs. However, the values of an effective number of codons (ENC) revealed that the bias was of low magnitude. Principal component analysis, ENC-plot, parity rule two analysis and correlation analysis suggested that natural selection and mutation pressure were both involved in the shaping of the codon usage patterns of PCVs. However, a neutrality plot revealed a stronger effect of natural selection than mutation pressure on codon usage patterns. Good host adaptation was also shown by the codon adaptation index analysis for all these viruses. Interestingly, obtained data suggest that PCV-4 might be more adapted to its host compared to other PCVs. The present study obtained insights into the codon usage pattern of PCVs based on ORF1 and ORF2, which further helps the understanding the molecular evolution of these swine viruses.

Phylogeography reveals association between swine trade and the spread of porcine epidemic diarrhea virus in China and across the world

The ongoing SARS (severe acute respiratory syndrome)-CoV (coronavirus)-2 pandemic has exposed major gaps in our knowledge on the origin, ecology, evolution, and spread of animal coronaviruses. Porcine epidemic diarrhea virus (PEDV) is a member of the genus Alphacoronavirus in the family Coronaviridae that may have originated from bats and leads to significant hazards and widespread epidemics in the swine population. The role of local and global trade of live swine and swine-related products in disseminating PEDV remains unclear, especially in developing countries with complex swine production systems. Here, we undertake an in-depth phylogeographic analysis of PEDV sequence data (including 247 newly sequenced samples) and employ an extension of this inference framework that enables formally testing the contribution of a range of predictor variables to the geographic spread of PEDV. Within China, the provinces of Guangdong and Henan were identified as primary hubs for the spread of PEDV, for which we estimate live swine trade to play a very important role. On a global scale, the United States and China maintain the highest number of PEDV lineages. We estimate that, after an initial introduction out of China, the United States acted as an important source of PEDV introductions into Japan, Korea, China, and Mexico. Live swine trade also explains the dispersal of PEDV on a global scale. Given the increasingly global trade of live swine, our findings have important implications for designing prevention and containment measures to combat a wide range of livestock coronaviruses.

Evidence of coinfection of pigs with African swine fever virus and porcine circovirus 2

Archival swine DNA samples from Indonesia and Mongolia, some of which were previously shown to be positive for African swine fever virus, were screened for the presence of porcine circovirus 2 (PCV-2) and porcine circovirus 3 (PCV-3) by PCR. Samples from both countries were positive for PCV-2 (three from Mongolia and two from Indonesia), while none were positive for PCV-3. The PCV-2 amplicons were sequenced, and phylogenetic analysis revealed that the PCV-2 strains belonged to four different genotypes: PCV-2a (Mongolia), PCV-2b (Mongolia and Indonesia), PCV-2d (Indonesia), and PCV-2g (Mongolia). This is the first report of ASFV/PCV-2 coinfection in pigs and the first report of the presence of PCV-2 in Mongolia.

Protective immunity induced by concurrent intradermal injection of porcine circovirus type 2 and Mycoplasma hyopneumoniae inactivated vaccines in pigs

Vaccines against porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae (Mhp) are routinely used by intramuscular injection. However, since intramuscular vaccination causes stress and increases the risk of cross-contamination among pigs, research on intradermal vaccination is currently being actively conducted. This study was designed to evaluate the efficacy of intradermally administered inactivated vaccines against PCV2 and Mhp in pigs. Three-week-old specific pathogen-free pigs were divided into three groups (5 pigs per group). Pigs in the two groups were intradermally vaccinated with the PCV2 or Mhp vaccine using a needle-free injector. Pigs in the third group were kept as nonvaccinated controls. At 21 days post-vaccination, pigs in one of these vaccinated groups and the nonvaccinated group were intranasally challenged with PCV2b and Mhp, while the other vaccinated group pigs were maintained as vaccine controls. Vaccine efficacy was evaluated by observing weight gain, pathogen load, pathological changes, and humoral or cellular immune responses. As a result, vaccinated pigs revealed significantly higher body weight gain, with lower clinical scores. Vaccinated pigs also showed higher antibody responses but lower PCV2b or Mhp loads in sera, nasal swabs, or lungs than nonvaccinated pigs. Intriguingly, vaccinated pigs upregulated cytotoxic T cells (CTLs), helper T type 1 cells (Th1 cells), and helper T type 17 cells (Th17 cells) after immunization and showed significantly higher levels of CTLs, Th1 and Th17 cells at 14 days post-challenge than nonvaccinated and challenged pigs. This study demonstrated that protective immune responses against PCV2 and Mhp could be efficiently induced in pigs using a relatively small volume of intradermal vaccines, probably due to effective antigen delivery to antigen-presenting cells in the dermis.

Retrospective surveillance of porcine circovirus 4 in pigs in Inner Mongolia, China, from 2016 to 2018

A novel circovirus designated "porcine circovirus type 4" (PCV4) was recently reported in pigs with severe clinical disease in Hunan Province, China. Relatively little is known about the molecular epidemiology of this recently discovered virus. In order to assess the prevalence of PCV4 infection in pigs and to analyze its genomic characteristics, 1683 clinical samples were collected in Inner Mongolia, China, from 2016 to 2018. The overall infection rate of PCV4 was 1.6% (27/1683) at the sample level and 21.6% (11/51) at the farm level, with rates ranging from 3.2% (1/31) to 20.0% (6/30) on different PCV4-positive pig farms. In addition, the PCV4 infection rates at both the sample and farm level increased from 2016 to 2018. This also showed that PCV4 was present in pigs in 2016 in China and therefore did not arrive later than this date. Additionally, our findings showed that PCV4 infections had no association with PCV2 or PCV3 infections. We sequenced the complete genomes of three PCV4 strains and found that the PCV4 strains had a high degree of genetic stability but shared less than 80% sequence identity with other circoviruses. We identified six amino acid mutations in the Rep protein and seven in the Cap protein. Phylogenetic analysis based on Cap and Rep sequences confirmed that the PCV4 strains grouped in an independent branch. Our findings provide important information about the prevalence and genetic characteristics of PCV4 strains.

Porcine Circovirus Type 3 Enters Into PK15 Cells Through Clathrin- and Dynamin-2-Mediated Endocytosis in a Rab5/Rab7 and pH-Dependent Fashion

Porcine circovirus type 3 (PCV3) invades multiple tissues and organs of pigs of different ages and are widely spread throughout pig farms, emerging as an important viral pathogen that can potentially damage the pig industry worldwide. Since PCV3 is a newly discovered virus, many aspects of its life cycle remain unknown. Porcine kidney epithelial cells are important host targets for PCV3. Here, we used systematic approaches to dissect the molecular mechanisms underlying the cell entry and intracellular trafficking of PCV3 in PK15 cells, a cell line of porcine kidney epithelial origin. A large number of PCV3 viral particles were found to colocalize with clathrin but not caveolin-1 after entry, and PCV3 infection was significantly decreased when treated with chlorpromazine, dynasore, knockdown of clathrin heavy chain expression via RNA interference, or overexpression of a dominant-negative mutant of EPS15 in PCV3-infected cells. After internalization, the viral particles were further observed to colocalize with Rab5 and Rab7, and knockdown of both expression by RNA interference significantly inhibited PCV3 replication. We also found that PCV3 infection was impeded by ammonium chloride treatment, which indicated the requirement of an acidic environment for viral entry. Taken together, our findings demonstrate that PCV3 enters PK15 cells through a clathrin- and dynamin-2-mediated endocytic pathway, which requires early and late endosomal trafficking, as well as an acidic environment, providing an insightful theoretical basis for further understanding the PCV3 life cycle and its pathogenesis.

Epidemiological investigation of porcine circovirus type 2 and its coinfection rate in Shandong province in China from 2015 to 2018

BACKGROUND

Porcine circovirus type 2 (PCV2) is one of the crucial swine viral pathogens, caused porcine circovirus associated diseases (PCVAD). Shandong province is one of the most important pork producing areas and bears a considerable economic loss due to PCVAD. However, there is limited information on epidemiology and coinfection rate of PCV2 with other critical swine diseases in this area, such as porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), Pseudorabies virus (PRV), and porcine epidemic diarrhea virus (PEDV).

RESULTS

Overall, 89.59% serum samples and 36.98% tissue samples were positive for PCV2 specified ELISA and PCR positive for PCV2, respectively. The coinfection rates of PCV2 with PRRSV, PRV, CSFV, and PEDV were 26.73%, 18.37%, 13.06%, and 3.47%, respectively. Moreover, genetic characteristic of PCV2 were analyzed based on the cap genes showing that PCV2d is the dominant sub-genotype circulating in the province.

CONCLUSIONS

Our findings reveal that PCV2d, as the dominant strain, is prevailing in pig farms in Shandong province at high levels. There was a high frequency of coinfection of PCV2 and PRRSV.

The combined usage of Matrine and Osthole inhibited endoplasmic reticulum apoptosis induced by PCV2

Background

Porcine circovirus type 2 (PCV2) is an important and common DNA virus that infect pig and can cause immunosuppression and induce apoptosis in the infected cells. To escape the host immune system, PCV2 constantly builds up complex mechanisms or mutates genes, and that is why it is difficult to eradicate complex PCV2 infection by relying on vaccines and single compound. At present, there is few literature reports on the effective prevention and treatment of PCV2 infection by a combination of two or more compounds. Previously, we have demonstrated the anti-PCV2 effect of Matrine in vitro, but its mechanism has not been further evaluated. Literatures have proven that Osthole has a variety of pharmacological activities, and we tested the ability of Osthole to inhibit PCV2 replication in cell culture. Therefore, this study explored the synergistic antiviral effect of Matrine combined with Osthole and their synergistic anti-apoptotic mechanism.

Results

Osthole alone had an anti-PCV2 effect, and then its synergistic anti-PCV2 effect of Osthole and Matrine was better than that of Matrine or Osthole alone as demonstrated by qRT-PCR, IFA and Western blotting results. The anti-apoptotic mechanism of these two compounds by inducing the PERK pathway by PCV2 was elucidated through Annexin V-FITC/PI, JC-1 and Western blotting. Matrine and Osthole combination could inhibit the expression of Cap in Cap-transfected PK-15 cells, thus inhibiting Cap-induced PERK apoptosis. Ribavirin was used as a positive control.

Conclusions

The combination of Osthole and Matrine had the synergistic effect of anti-PCV2 infection by directly inhibiting the expression of PCV2 Cap protein. The combination of these two compounds also inhibited PERK apoptosis induced by PCV2 Cap protein, possibly by regulating the level of GRP78. The results formed a base for further studies on the mechanism of anti-PCV2 in vivo using Matrine and Osthole combination and developing new anti-PCV2 compounds with Cap and GRP78 as therapeutic targets.

Cepharanthine and Curcumin inhibited mitochondrial apoptosis induced by PCV2

Background

Porcine circovirus type 2 (PCV2) is an immunosuppressive pathogen with high prevalence rate in pig farms. It has caused serious economic losses to the global pig industry. Due to the rapid mutation of PCV2 strain and co-infection of different genotypes, vaccination could not eradicate the infection of PCV2. It is necessary to screen and develop effective new compounds and explore their anti-apoptotic mechanism. The 13 natural compounds were purchased, with a clear plant origin, chemical structure and content and specific biological activities.

Results

The maximum no-cytotoxic concentration (MNTC) and 50% cytotoxic concentration (CC₅₀) of 13 tested compounds were obtained by the cytopathologic effect (CPE) assay and (3-(4,5-dimethyithiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method in PK-15 cells. The results of qPCR and Western blot showed that, compared with the PCV2 infected group, the expression of Cap in Paeonol (0.4 mg/mL and 0.2 mg/mL), Cepharanthine (0.003 mg/mL, 0.0015 mg/mL and 0.00075 mg/mL) and Curcumin (0.02 mg/mL, 0.001 mg/mL and 0.005 mg/mL) treated groups were significantly lowered in a dose-dependent manner. The results of Annexin V-FITC/PI, JC-1, Western blot and ROS analysis showed that the expression of cleaved caspase-3 and Bax were up-regulated Bcl-2 was down-regulated in Cepharanthine or Curcumin treated groups, while ROS and MMP value were decreased at different degrees and the apoptosis rate was reduced. In this study, Ribavirin was used as a positive control.

Conclusions

Paeonol, Cepharanthine and Curcumin have significant antiviral effect. And the PCV2-induced Mitochondrial apoptosis was mainly remitted by Cepharanthine and Curcumin.

Immune responses induced by a combined vaccination with a recombinant chimera of Mycoplasma hyopneumoniae antigens and capsid virus-like particles of porcine circovirus type 2

BACKGROUND

Mycoplasma hyopneumoniae (Mhp) and porcine circovirus type 2 (PCV2) are two important pathogens causing Mycoplasma pneumonia of swine (MPS) and porcine circovirus diseases and porcine circovirus-associated diseases (PCVDs/PCVADs), respectively, and resulted in considerable economic loss to the swine industry worldwide. Currently, vaccination is one of the main measures to control these two diseases; however, there are few combination vaccines that can prevent these two diseases. To determine the effect of combination immunization, we developed capsid-derived (Cap) virus-like particles (VLPs) of PCV2 and a new recombinant chimera composed of the P97R1, P46, and P42 antigens of Mhp. Then we investigated the immune responses induced by the immunization with this combination vaccine in mice and piglets.

RESULTS

The high level antibodies against three protein antigens (P97R1, P46, and P42 of Mhp) were produced after immunization, up to or higher than 1:400,000; the antibody levels in Pro group continuously increased throughout the 42 days for all the antigens tested. The lymphocyte proliferative response in PCV2 group was stronger than that in PBS, VP, Mhp CV in mice. The antibody levels for Cap remained stable and reached the peak at 35 DAI. The IFN-γ and IL-4 in sera were significantly enhanced in the Pro group than that in the negative control-VP group on Day 14 and 28 post-the first immunization in piglets.

CONCLUSIONS

Above all, the combination immunization could induce humoral and cellular immune responses against all four antigens in mice and piglets. Therefore, our approach is a simple and effective vaccination strategy to protect pigs against MPS and PCVD/PCVAD.

Prevalence, pathogenesis, and evolution of porcine circovirus type 3 in China from 2016 to 2019

Porcine circovirus type 3 (PCV3) infection causes substantial economic losses in pig populations since its discovery in 2016. However, PCV3 molecular epidemiology remains need further study. In order to assess the prevalence of PCV3 infection in China, 4094 clinical samples from 271 pig farms in 10 provinces of China were evaluated by PCR. It was shown that the overall prevalence of PCV3 infection was 29.3 % (1200/4094) and 74.2 % (201/271) at sample and farm levels respectively, suggesting that PCV3 infection is prevalent in China. Furthermore, a statistical analysis showed PCV3 might exacerbate PCV2 and PRRSV infection rate and have a potential association with pig clinical disease. In addition, we sequenced the entire genome of 57 PCV3 strains; homology analysis showed that PCV3 strains have more than 96 % similarities at the nucleotide level, and PCV3 shares less than 60 % similarities with other circoviruses. By comparing the total 673 PCV3 strains from the NCBI GenBank, we found the major of amino acid mutations are located in predicted epitope regions and the mutations ratio changed during PCV3 evolution. Phylogenetic analysis revealed that all isolates belonged to PCV3a and PCV3b, and increasing PCV3a and decreasing PCV3b trends were observed during PCV3 evolution. Overall, this study provides important insights for understanding PCV3 prevalence, pathogenesis, and evolution and will guide future efforts to develop effective preventive and control measures.

Co-infection status of porcine circoviruses (PCV2 and PCV3) and porcine epidemic diarrhea virus (PEDV) in pigs with watery diarrhea in Henan province, central China

Porcine circoviruses (PCV2 and PCV3) and porcine epidemic diarrhea virus (PEDV) are important swine viruses that threaten the swine industry worldwide. Here, we evaluated the co-infection status of PCV2, PCV3 and PEDV in 76 enteric samples from piglets with severe diarrhea disease in Henan, China. All samples were tested by PCR/RT-PCR. Our results showed that the infection rate of PCV2, PCV3 and PEDV was 82.89%, 76.32% and 68.42%, respectively. Interestingly, most of these samples exhibited mixed infections. The co-infection rates of PCV2 and PCV3, PCV2 and PEDV, PCV3 and PEDV were 69.74%, 57.89% and 53.95%, respectively. And the triple infection rate was 48.68%. Furthermore, the genetic characteristics of PCV2 and PCV3 were analyzed based on the cap genes. Two PCV2 genotypes, PCV2b and PCV2d, were circulating in the fields. The cap gene of PCV2b and PCV2d isolates only shared 94.6%-95.0% nucleotide identities. The PCV3 isolates together with the reference strains could be divided into four clades (clade1-4), and the cap genes of these isolates have 98.6%-100% nucleotide identities to each other. Distinctive amino acid substitutions were also characterized on the cap protein of PCV2 and PCV3 isolates. Our studies provide the new knowledge on the co-infectious status of PCV2, PCV3 and PEDV in China. The results also provide insight into the genetic diversity and molecular epidemiology of PCV2 and PCV3.

Phylogenetic analysis of porcine circovirus type 2 (PCV2) between 2015 and 2018 in Henan Province, China

Background

Porcine circovirus type 2 (PCV2) is the pathogen of porcine circovirus associated diseases (PCVAD) and one of the main pathogens in the global pig industry, which has brought huge economic losses to the pig industry. In recent years, there has been limited research on the prevalence of PCV2 in Henan Province. This study investigated the genotype and evolution of PCV2 in this area.

Results

We collected 117 clinical samples from different regions of Henan Province from 2015 to 2018. Here, we found that the PCV2 infection rate of PCV2 was 62.4%. Thirty-seven positive clinical samples were selected to amplify the complete genome of PCV2 and were sequenced. Based on the phylogenetic analysis of PCV2 ORF2 and complete genome, it was found that the 37 newly detected strains belonged to PCV2a (3 of 37), PCV2b (21 of 37) and PCV2d (13 of 37), indicating the predominant prevalence of PCV2b and PCV2d strains. In addition, we compared the amino acid sequences and found several amino acid mutation sites among different genotypes. Furthermore, the results of selective pressure analysis showed that there were 5 positive selection sites.

Conclusions

This study indicated the genetic diversity, molecular epidemiology and evolution of PCV2 genotypes in Henan Province during 2015–2018.

Molecular Detection and Genetic Diversity of porcine Circovirus Type 3 in Commercial Pig Farms in Xinjiang Province, China

Introduction

Porcine circovirus type 3 (PCV3) is a newly discovered porcine circovirus. The molecular characteristics and genetic evolution of PCV3 in Xinjiang province, China still being unclear, the aim of the study was their elucidation.

Material and Methods

A total of 393 clinical samples were collected from pigs on commercial farms in nine different regions of Xinjiang and phylogenetic analysis based on full-length Cap genes was performed.

Results

The prevalence at farm level was 100%, while in all the tested samples it was 22.39%. Nine PCV3 strains were detected in Xinjiang province and they shared 98.9–99.3% nucleotide and 97.5–100.0% Cap gene amino acid sequence identities with other epidemic strains from China and abroad. Compared with other epidemic strains of PCV3, there were 26 base mutation sites in the Cap gene in the nine Xinjiang strains, resulting in the mutation of amino acids at positions 20, 24, 75, 77, 108, 111 and 206. Phylogenetic analysis showed that these strains can be divided into two different genetic groups, to the first of which five strains affiliated and divided between subgroups 1.1 and 1.2, and to the second of which the other four strains affiliated and similarly divided between subgroups 2.1 and 2.2.

Conclusion

PCV3 circulates widely among commercial pig farms in Xinjiang province, China, and displays obvious genetic diversity. The results provide epidemiological information useful for the prevention and control of PCV3 infection in the pig industry.

ITRAQ-based quantitative proteomics reveals the first proteome profiles of piglets infected with porcine circovirus type 3

Porcine circovirus type 3 (PCV3) infection induces porcine dermatitis and nephropathy syndrome, reproductive failure, and multisystemic inflammatory lesions in piglets and sows. To better understand the host responses to PCV3 infection, isobaric tags for relative and absolute quantification (iTRAQ) labeling combined with LC-MS/MS analysis was used for quantitative determination of differentially regulated cellular proteins in the lungs of specific-pathogen-free piglets after 4 weeks of PCV3 infection. Totally, 3429 proteins were detected in three independent mass spectrometry analyses, of which 242 differential cellular proteins were significantly regulated, consisting of 100 upregulated proteins and 142 downregulated proteins in PCV3-infected group relative to control group. Bioinformatics analysis revealed that these higher or lower abundant proteins involved primarily metabolic processes, innate immune response, MHC-I and MHC-II components, and phagosome pathways. Ten genes encoding differentially regulated proteins were selected for investigation via real-time RT-PCR. The expression levels of six representative proteins, OAS1, Mx1, ISG15, IFIT3, SOD2, and HSP60, were further confirmed by Western blotting and immunohistochemistry. This study attempted for the first time to investigate the protein profile of PCV3-infected piglets using iTRAQ technology; our findings provide valuable information to better understand the mechanisms underlying the host responses to PCV3 infection in piglets. SIGNIFICANCE: Our study identified differentially abundant proteins related to a variety of potential signaling pathways in the lungs of PCV3-infected piglets. These findings provide valuable information to better understand the mechanisms of host responses to PCV3 infection.

First detection and genomic characterization of porcine circovirus 3 in mosquitoes from pig farms in China

The porcine circovirus type 3 (PCV3) becomes an important causative agent of swine disease since its discovery in 2016. PCV3 infection exhibits a wide range of clinical syndromes causing substantial economic losses in swine industry. Previous studies have reported the detection of numerous known viruses including circovirus in mosquitoes. However, the transmission of PCV3 in field-caught mosquitoes remains largely unknown. This study aims to detect PCV3 infection in mosquitoes and analyze its genomic characteristics. Here, we performed a PCR to detect the PCV3 in 269 mosquito samples collected from pig farms located in Heilongjiang, Jilin, and Yunnan provinces. The proportion of PCV3-positive mosquitoes was 32.0 % (86/269), ranging from 21.4%-42.5% at farm level, which may imply that mosquito serves as a route of transmission for PCV3. To determine the possible origin of PCV3 in mosquitoes, 80 pig serum samples were collected from the pig farms where mosquito sampling was also performed. The proportion of PCV3-positive farms ranged from 15.0%-30.0 % in which infection of positive pigs positively correlated with mosquitoes carrying the virus. Additionally, we sequenced the entire genome of 6 strains of PCV3 in mosquitoes and 2 strains of PCV3 in pigs. Sequence analysis indicated a 100 % nucleotide similarity between mosquito and pig viral isolates that were all collected from similar farms. Phylogenetic analysis showed that PCV3 could be divided into two clades, PCV3a and PCV3b, and the PCV3 strains isolated in mosquitoes were distributed on the two clades. Our results demonstrate that mosquitoes may serve as a potential transmission vector in the life-cycle of PCV3, revealing possible transmission routes of PCV3.

Identification of Nuclear Localization Signals in the ORF2 Protein of Porcine Circovirus Type 3

Porcine circovirus type 3 (PCV3) contains two major open reading frames (ORFs) and the ORF2 gene encodes the major structural capsid protein. In this study, nuclear localization of ORF2 was demonstrated by fluorescence observation and subcellular fractionation assays in ORF2-transfected PK-15 cells. The subcellular localization of truncated ORF2 indicated that the 38 N-terminal amino acids were responsible for the nuclear localization of ORF2. The truncated and site-directed mutagenesis of this domain were constructed, and the results demonstrated that the basic amino acid residues at positions 8-32 were essential for the strict nuclear localization. The basic motifs ₈RRR-R-RRR₁₆ and ₁₆RRRHRRR₂₂ were further shown to be the key functional nucleolar localization signals that guide PCV3 ORF2 into nucleoli. Furthermore, sequence analysis showed that the amino acids of PCV3 nuclear localization signals were highly conserved. Overall, this study provides insight into the biological and functional characteristics of the PCV3 ORF2 protein.

Enhanced protective immune response to PCV2 adenovirus vaccine by fusion expression of Cap protein with InvC in pigs

The major immunogenic protein capsid (Cap) of porcine circovirus type 2 (PCV2) is critical to induce neutralizing antibodies and protective immune response against PCV2 infection. This study was conducted to investigate the immune response of recombinant adenovirus expressing PCV2b Cap and C-terminal domain of Yersinia pseudotuberculosis invasin (Cap-InvC) fusion protein in pigs. The recombinant adenovirus rAd-Cap-InvC, rAd-Cap and rAd were generated and used to immunize pigs. The phosphate-buffered saline was used as negative control. The specific antibodies levels in rAd-Cap-InvC and ZJ/C-strain vaccine groups were higher than that of rAd-Cap group (p < 0.05), and the neutralization antibody titer in rAd-Cap-InvC group was significantly higher than those of other groups during 21–42 days post-immunization (DPI). Moreover, lymphocyte proliferative level, interferon-γ and interleukin-13 levels in rAd-Cap-InvC group were increased compared to rAd-Cap group (p < 0.05). After virulent challenge, viruses were not detected from the blood samples in rAd-Cap-InvC and ZJ/C-strain vaccine groups after 49 DPI. And the respiratory symptom, rectal temperature, lung lesion and lymph node lesion were minimal and similar in the ZJ/C-strain and rAd-Cap-InVC groups. In conclusion, our results demonstrated that rAd-Cap-InvC was more efficiently to stimulate the production of antibody and protect pigs from PCV2 infection. We inferred that InvC is a good candidate gene for further development and application of PCV2 genetic engineering vaccine.

Reservoirs of Porcine Circoviruses: A Mini Review

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.

Emergence of a novel recombinant porcine circovirus type 2 in China: PCV2c and PCV2d recombinant

Porcine circovirus type 2 (PCV2) has been causing huge economic losses in Chinese swine herds since it was first identified in China in 1999. Genotypes of PCV2 except for PCV2c coexist in swine herds in China, which may facilitate virus recombination. In the current study, six novel PCV2 strains were detected in China, and these strains shared high nucleotide similarity of the Rep gene with the PCV2c strain DK1987PMWSfree and high homology of the Cap gene with PCV2d. Genome sequence analysis revealed that the complete genomes of these strains were 1767 nucleotides (nt) in length and shared 99.8%-99.9% nucleotide identity with each other and 91.7%-98.7% with representative strains. Phylogenetic analysis, sequencing analysis, base-by-base comparisons and comprehensive recombination analysis demonstrated that these six strains originated from recombination within the Rep gene between PCV2c and PCV2d strains. Surprisingly, further investigation through theoretical recombination analysis of Chinese PCV2 GenBank sequences showed that these novel patterns of recombinant PCV2 strains have been generated since 2010. Collectively, our findings provide additional evidence of inter-genotypic recombination of PCV2.

The prevalence and genetic diversity of porcine circovirus types 2 and 3 in Northeast China from 2015 to 2018

A total of 472 samples from domestic pigs collected in China from 2015 to 2018 were tested for the presence of porcine circovirus types 2 and 3 (PCV2 and PCV3, respectively) by conventional polymerase chain reaction analysis. The prevalence of PCV2, PCV3, and PCV2/3 co-infection was 50.0%, 13.3%, and 6.78%, respectively. The complete genomic sequences of 66 PCV2 isolates and four PCV3 isolates were determined. Based phylogenetic analysis, the PCV2 isolates were assigned to three genotypes, PCV2a, PCV2b, and PCV2d, representing 13.6% (9/66), 25.8% (17/66), and 60.6% (40/66) of the total, respectively. All four PCV3 isolates shared a high degree of similarity in their complete nucleotide sequences (98.8-99.8% identity) and ORF2 amino acid sequences (98.6-99.5% identity). These results indicate that all three PCV2 genotypes (PCV2a, PCV2b, and PCV2d) are present on pig farms and that PCV2d has become the predominant genotype. The predicted amino acid sequences of the four PCV3 isolates indicated that PCV3-CN-JL53/PCV3-CN-LN56, PCV3-CN-HLJ3, and PCV3-CN-0710, belonged to the genotypes PCV3a, PCV3b, and PCV3a-IM, respectively. In view of the great harm that PCV2 causes to the pig industry, the epidemic trend of PCV3 should continue to be closely monitored. This study provides information about the prevalence, genetic diversity, and molecular epidemiology of PCV2 and PCV3 in China from 2015 to 2018.

First detection and phylogenetic analysis of porcine circovirus type 2 in raccoon dogs

Background

Porcine circovirus type 2 (PCV2) is a major emerging virus of porcine circovirus-associated disease (PCVAD), which has brought huge economic losses to the global pig industry. Pigs are well known as the natural reservoir of PCV2. Recently, many researchers have revealed PCV2 could infect many other mammals like mice, calves, minks, dogs and goats. In 2018, our laboratory has admitted six cases of raccoon dogs from Qinhuangdao city of China, which were characterized by inappetence, lethargy, depression, abortion, and sterility.

Results

At last, six raccoon dog-origin PCV2 strains were isolated in this study. Pairwise-sequence comparisons demonstrated that the six raccoon dog-origin PCV2 strains shared a nucleotide similarity of 92.1–99.8% among 40 PCV2 representative strains. Phylogenetic analysis indicated these PCV2 isolates belonged to Chinese epidemic genotypes PCV2b and PCV2d. And aborted or sterile symptom was significantly associated with PCV2 infection in raccoon dogs by the chi-square test (χ² = 87.3, p < 0.001). The retrospective study revealed that raccoon dog-origin PCV2 strains shared 100% sequence similarity with the PCV2 stains isolated from pig farms around these raccoon dog farms, respectively.

Conclusion

In this study, the first supported evidence of PCV2 prevalence in raccoon dog farms of China was documented. PCV2 may be one of the most significant causative agents resulting in the reproductive failure of farmed raccoon dogs, implying that PCV2 could transmit from pigs to raccoon dogs. That indicated that PCV2 cross-species transmission will be a serious threat to China’s fur animal farming industry.

First detection and genetic analysis of fox-origin porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a causative agent of porcine circovirus-associated disease (PCVAD), which is a serious problem in the swine industry worldwide. In recent years, nonporcine-origin PCV2 has attracted more and more attention of the researchers. This study reported on the first identification of PCV2 in farmed foxes with reproductive failure. Three fox-origin PCV2 strains were successfully isolated, sequenced, and designated as FoxHB1, FoxHB2, and FoxHB3 respectively. Pairwise-sequence comparisons of the complete genomes revealed that three fox-origin PCV2 strains had nucleotide identities varied from 91.9% to 99.7% with representative strains of PCV2 different genotypes. Meanwhile, phylogenetic analysis based on complete genomes of 44 PCV2 strains indicated that the fox-origin PCV2 strains belonged to Chinese epidemic genotypes PCV2b and PCV2d. These results provided the first supported evidence that PCV2 could infect foxes, implying that the cross-species transmission of PCV2 would be a big threat to Chinese fur animal-bearing industry.

Regulation of Apoptosis During Porcine Circovirus Type 2 Infection

Apoptosis, an indispensable innate immune mechanism, regulates cellular homeostasis by removing unnecessary or damaged cells. It contains three signaling pathways: the mitochondria-mediated pathway, the death receptor pathway and the endoplasmic reticulum pathway. The importance of apoptosis in host defenses is stressed by the observation that multiple viruses have evolved various strategies to inhibit apoptosis, thereby blunting the host immune responses and promoting viral propagation. Porcine Circovirus type 2 (PCV2) utilizes various strategies to induce or inhibit programmed cell death. In this article, we review the latest research progress of the apoptosis mechanisms during infection with PCV2, including several proteins of PCV2 regulate apoptosis via interacting with host proteins and multiple signaling pathways involved in PCV2-induced apoptosis, which provides scientific basis for the pathogenesis and prevention of PCV2.

Production of a monoclonal antibody against Porcine circovirus type 3 cap protein

Porcine cirvovirus type 3 (PCV3) is a newly emerging swine virus with worldwide distribution. The pathogenesis of PCV3 remains unknown due to failures in propagating and isolating the virus on successive cell lines. The virus cap protein is the only structural protein of PCV3 and no monoclonal antibodies against it are available. Although antisera are available from PCV3-infected pigs, they are not suitable for immunoassays such as immunohistochemical staining of infected tissues due to high non-specific background. Developing monoclonal antibodies against the cap protein is indispensable for elucidating PCV3 biological properties. In this study, a monoclonal antibody (mAb 1H1) with a titer of 1/25,600 that recognized the PCV3 cap protein was developed. Western-blot results showed that mAb 1H1 reacted strongly with the recombinant PCV3 cap protein preparation but not with the PCV2 cap protein. MAb 1H1 was also applied successfully for the detection of the cap protein in PCV3-infected pig tissues using immunochemistry staining. In conclusion, mAb 1H1 has significant potential uses in PCV3 diagnosis as well as the study of PCV3 biology.

Detection and genetic characterisation of porcine circovirus 3 from pigs in Sweden

Porcine circovirus 3 (PCV3) is a newly detected circovirus belonging to the family Circoviridae with a circular ssDNA genome of 2000 bp that encodes two proteins-the replicase protein and the capsid protein. PCV3 was discovered for the first time in the US in 2016. After this initial discovery, PCV3 was detected in other parts of the world such as in China, South Korea, Italy and Poland. In this study, 49 tissue samples from Swedish pig herds were screened for PCV3 using PCR and 10 samples were positive and one was uncertain. The entire PCV3 genome and a mini PCV-like virus (MPCLV) were obtained from one of these samples. These two viruses showed a high sequence identity to PCV3 viruses from other countries as well as to MPCLV from the US. However, the sequence identity to PCV1 and 2 was only 31-48% on amino acid level. This is the first detection and complete genetic characterisation of PCV3 in Swedish pigs. It is also interesting to note that one of the positive samples was collected in 1993, showing that PCV3 has been present for a long time.

A Duplex Real-Time PCR Assay for the Simultaneous Detection of Porcine Circovirus 2 and Circovirus 3

Porcine circoviruses (PCV) include PCV1, PCV2, and the new-emerging PCV3. PCV2 is pathogenic to pigs, but the pathogenicity of PCV3 in pigs is debatable. Recently, there have been frequent reports of PCV2 and PCV3 co-infections in clinical samples. Thus, it would be practical to develop a duplex PCR method to detect PCV2 and PCV3 simultaneously. In this study, specific primers and probes were designed to target PCV2 cap and PCV3 rep genes. A duplex real-time PCR method was then developed to detect the two viruses. The assay was found to be highly specific, sensitive, and reproducible for PCV2/3 without cross-reactions with other swine pathogens. The sensitivity of this assay was 2.9 copies for the PCV2 plasmid and 22.5 copies for the PCV3 plasmid. The established assay was then used to detect PCV2/3 infection in 340 clinical samples collected in the first half of 2017. The results showed that the co-infection rate of PCV2/3 in the samples was 27.6%. Our study provides an important tool that can be used to perform urgently needed surveys for the two porcine circoviruses to evaluate their impact on the swine industry.

High prevalence of PCV2d in Hunan province, China: a retrospective analysis of samples collected from 2006 to 2016

Porcine circovirus 2 (PCV2) has been widely prevailing in China since the first report in 2001, causing huge economic losses to the pig industry. In the present study, 674 samples were collected from 2006 to 2016 in Hunan province, and 62% were positive for PCV2. An increase was observed from 2006 to 2011 (72.1%-89.1%), and a decrease was observed from 2012 to 2016 (78.9%-36.8%). The prevalence of genotype PCV2a, PCV2b, and PCV2d was 0, 44.7% and 67%, respectively. During 2006-2007, PCV2b was the main genotype circulating in Hunan, while, in 2008, PCV2d became the predominant one. Coinfection with PCV2b and PCV2d was observed frequently, and the positive rates of coinfection ranged from 6.3% to 18.9% during 2006-2016. The complete genome was sequenced for 54 positive samples, and four were identified as PCV2b-1, 22 as PCV2b-2, four as PCV2d-1 and 24 as PCV2d-2, based on phylogenetic analysis of the complete genome and ORF2 region. Recombination analysis using the complete genome sequences of these isolates revealed a high recombination rate of 27.7% (17/54), and showed that recombination occurred mainly in the ORF1 region. This shows that the prevalence of PCV2 has clearly decreased in recent years and that PCV2d has become a predominant genotype since 2008. In addition, frequent recombination events were observed in the PCV2 isolates from Hunan, China.

Molecular detection of novel circoviruses in ticks in northeastern China

Novel circular single-stranded DNA (ssDNA) genomes have been found in various animals using high-throughput sequencing techniques. In this study, two circular ssDNA genomes were detected in adult ticks from northeastern China by Solexa sequencing and PCR. The two sequences shared a similar genomic organization to circoviruses, with genomes of 1936 bp (TiCV-1) and 1812 bp (TiCV-2), each including two major open read frames (ORFs), ORF1 and ORF2, encoding putative replicase and capsid proteins, respectively. The potential stem-loop structure of a circovirus was predicted in the intergenic region between the two ORFs. Sequence comparison showed that the genome of TiCV-2 was almost the same as that of TiCV-1, except for two deletions and several mutations, and they had a high identity of 71.3-72.9% with Raven circovirus. The infection rates of circoviruses were calculated by the maximum likelihood estimation as 3.2% (95% CI, 1.9-5.2%) for TiCV-1 in the investigated Haemaphysalis longicornis, and 1.2% (95% CI, 0.2-4.0%) for TiCV-2 in Ixodes crenulatus from Yichun of Heilongjiang Province. These results indicate that the two sequences are distantly related to known circovirus genomes and may represent novel species in the family Circoviridae.