Ubiquitination-dependent degradation of nucleolin mediated by porcine circovirus type 3 capsid protein.

IMPORTANCE: Porcine circovirus type 3 (PCV3) is an emerging pathogen that causes multisystem disease in pigs and poses a severe threat to the swine industry. However, the mechanisms of how PCV3 uses host proteins to regulate its own life cycle are not well understood. In this study, we found that PCV3 capsid protein interacts with nucleolin and degrades it. Degradation of nucleolin by the PCV3 capsid protein requires recruitment of the enzyme RNF34, which is transported to the nucleolus from the cytoplasm in the presence of the PCV3 capsid protein. Nucleolin also decreases PCV3 replication by promoting the release of interferon ß. These findings clarify the mechanism by which nucleolin modulates PCV3 replication in cells, thereby facilitating to provide an important strategy for preventing and controlling PCV3 infection.

Porcine Circovirus 2 Activates the PERK-Reactive Oxygen Species Axis To Induce p53 Phosphorylation with Subsequent Cell Cycle Arrest at S Phase in Favor of Its Replication.

Porcine circovirus type 2 (PCV2), the causative agent of porcine circovirus-associated diseases (PCVAD), is known to induce oxidative stress, activate p53 with induction of cell cycle arrest, and trigger the PERK (protein kinase R-like endoplasmic reticulum kinase) branch of the endoplasmic reticulum (ER) stress pathway. All these cellular responses could enhance PCV2 replication. However, it remains unknown whether PERK activation by PCV2 is involved in p53 signaling with subsequent changes of cell cycle. Here, we demonstrate that PCV2 infection induced cell cycle arrest at S phase to favor its replication via the PERK-reactive oxygen species (ROS)-p53 nexus. PCV2 infection promoted phosphorylation of p53 (p-p53) at Ser15 in porcine alveolar macrophages. Inhibition of PERK by RNA silencing downregulated total p53 (t-p53) and p-p53. Treatment with the MDM2 inhibitor nutlin-3 led to partial recovery of t-p53 in perk-silenced and PCV2-infected cells. perk silencing markedly downregulated ROS production. Scavenging of ROS with N-acetylcysteine (NAC) of PCV2-infected cells downregulated t-p53 and p-p53. Increased accumulation of p-p53 in the nuclei during PCV2 infection could be downregulated by silencing of perk or NAC treatment. Further studies showed that perk silencing or NAC treatment alleviated S phase accumulation and downregulated cyclins E1 and A2 in PCV2-infected cells. These findings indicate that the PCV2-activated PERK-ROS axis promotes p-p53 and contributes to cell cycle accumulation at S phase when more cellular enzymes are available to favor viral DNA synthesis. Overall, our study provides a novel insight into the mechanism how PCV2 manipulates the host PERK-ROS-p53 signaling nexus to benefit its own replication via cell cycle arrest. IMPORTANCE Coinfections or noninfectious triggers have long been considered to potentiate PCV2 infection, leading to manifestation of PCVAD. The triggering mechanisms remain largely unknown. Recent studies have revealed that PERK-mediated ER stress, oxidative stress, and cell cycle arrest during PCV2 infection are conducive to viral replication. However, how PCV2 employs such host cell responses requires further research. Here, we provide a novel mechanism of PCV2-induced ER stress and enhanced viral replication: the PCV2-activated PERK-ROS-p53 nexus increases S phase cell population, a cell cycle period of DNA synthesis favorable for PCV2 replication. The fact that PCV2 deploys the simple ROS molecules to activate p53 to benefit its replication provides novel insights into the triggering factors, that is, certain stimuli or management measures that induce ER stress with subsequent generation of ROS would exacerbate PCVAD. Use of antioxidants is justified on farms where PCVAD is severe.

Synergistic Pathogenicity by Coinfection and Sequential Infection with NADC30-like PRRSV and PCV2 in Post-Weaned Pigs.

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus (PCVs) are two major viruses that affect pigs. Coinfections between PRRSV and PCV2 are frequently reported in most outbreaks, with clinical presentations involving dyspnea, fever, reduced feed intake, weight loss, and death in fattening pigs. The NADC30-like PRRSV and PCV2d are the main circulating virus strains found in China. This study determines the impact of NADC30-like PRRSV and PCV2d mono-infection and coinfection on the immune system, organ pathology, and viral shedding in five-week-old post-weaned pigs. Pigs were randomly divided into six groups: PBS, PRRSV, PCV2, PRRSV-PCV2 coinfection (co), and PRRSV-PCV2 or PCV2-PRRSV sequential infections. Fever, dyspnea, decreased feed intake, weight loss, and pig deaths occurred in groups infected with PRRSV, Co-PRRSV-PCV2, and PRRSV-PCV2. The viral load was higher in Co-PRRSV-PCV2, PRRSV-PCV2, and PCV2-PRRSV than those mono-infected with PRRSV or PCV2. Additionally, cytokines (IFN-γ, TNF-α, IL-4, and IL-10) produced by pigs under Co-PRRSV-PCV2 and PRRSV-PCV2 groups were more intense than the other groups. Necropsy findings showed hemorrhage, emphysema, and pulmonary adhesions in the lungs of pigs infected with PRRSV. Smaller alveoli and widened lung interstitium were found in the Co-PRRSV-PCV2 and PRRSV-PCV2 groups. In conclusion, PRRSV and PCV2 coinfection and sequential infection significantly increased viral pathogenicity and cytokine responses, resulting in severe clinical signs, lung pathology, and death.

Novel Porcine Circoviruses in View of Lessons Learned from Porcine Circovirus Type 2-Epidemiology and Threat to Pigs and Other Species.

Porcine circovirus type 2 (PCV2) plays a key role in PCV2-associated disease (PCVAD) etiology and has yielded significant losses in the pig husbandry in the last 20 years. However, the impact of two recently described species of porcine circoviruses, PCV3 and PCV4, on the pork industry remains unknown. The presence of PCV3 has been associated with several clinical presentations in pigs. Reproductive failure and multisystemic inflammation have been reported most consistently. The clinical symptoms, anatomopathological changes and interaction with other pathogens during PCV3 infection in pigs indicate that PCV3 might be pathogenic for these animals and can cause economic losses in the swine industry similar to PCV2, which makes PCV3 worth including in the differential list as a cause of clinical disorders in reproductive swine herds. Moreover, subsequent studies indicate interspecies transmission and worldwide spreading of PCV3. To date, research related to PCV3 and PCV4 vaccine design is at early stage, and numerous aspects regarding immune response and virus characteristics remain unknown.

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.

Simultaneous detection and genetic characterization of porcine circovirus 2 and 4 in Henan province of China.

Porcine circovirus 4 (PCV4) was identified as a novel porcine circovirus in China in 2019. To investigate the prevalence and genetic characteristics of PCV2 and PCV4, 133 clinical samples (103 tissue samples and 30 serum samples) were collected from 30 different pig farms in Henan province of China, and a SYBR Green I-based duplex quantitative real-time polymerase chain reaction assay was established to detect PCV2 and PCV4 genomes simultaneously. The complete genome sequences of 20 PCV2 and 6 PCV4 strains from 19 and 6 clinical samples respectively were sequenced and analyzed. The results showed the detection limits of this assay were 80.2 copies/µL for PCV2 and 58.6 copies/µL for PCV4. The detection results of clinical samples revealed the PCV2 positive rate was 63.16% (84/133), the PCV4 positive rate was 33.33% (45/133), and the PCV2 and PCV4 co-infection positive rate was 21.05% (28/133). Among 20 PCV2 strains, 6 belonged to PCV2a, 6 belonged to PCV2b and 8 belonged to PCV2d. Co-infection with JZ1 (PCV2b) and JZ2 (PCV2d) strains was identified in one sample (JZ-1). Eleven putative recombination events were found through the recombination analysis, suggesting that the new PCV2 variant strains had circulated in Henan province, which contributes to our understanding of evolutionary characteristics of PCV2 in China. The possible genotypes of PCV4 strains were determined based on genomic sequences of 6 PCV4 strains in this study and 29 PCV4 reference strains available at GenBank. According to three different phylogenetic trees (ORF1, ORF2 and complete genome), all 35 PCV4 strains were clustered into two major genotypes (PCV4a and PCV4b), and 6 PCV4 strains in this study belonged to PCV4a. Additionally, the functional regions of PCV4 strains were predicted by comparison with other circoviruses, which are conducive to the further study of the biological functions of PCV4 genome.

A retrospective study reveals the Porcine circovirus-2f genotype predominant in the indigenous pig population of North-eastern India.

Porcine circovirus-2 (PCV2) is a widespread virus and presents sub-clinically in most of the swineherd. Globally, eight genotypes of PCV2 have been identified that is PCV2a to 2h. To determine the region-wide genotype distribution of PCV2 infection, with additional reference to indigenous breeds, a total of 1314 pig's clinical samples from the eight states of North-eastern India between 2011 and 2014; were analyzed. The overall prevalence rate of PCV2 in this region was 28.2% (370/1314) by PCR. The state-wise PCR based PCV2 prevalence rate was: Tripura (20.8%), Nagaland (25.0%), Meghalaya (25.8%), Assam (32.1%), Sikkim (32.6%), Manipur (33.3%), Mizoram (36.7%) and Arunachal Pradesh (42.3%). Subsequently, a total of 29 complete genomes of PCV2 were amplified and sequenced from these PCV2 positive samples. The phylogenetic tree represents that the 29 PCV2 isolates of this study were divided into four distinct genetic groups; PCV2a, PCV2b, PCV2d, and PCV2f. Among these, 14 PCV2 strains were classified as PCV2f, 13 classified as PCV2d, and one isolate of each classified as PCV2a and PCV2b. All the 14 PCV2f strains appeared from indigenous pigs of this region. Based on the date of collection, the present study further describes that the PCV2f genotypes circulate in the indigenous pigs' population back in 2011. The amino acid residues and the atomic coordinate structure (3D model) of PCV2f capsid protein represents similarity to PCV2d capsid protein support the efficacy of the existing PCV2 vaccine against the PCV2f. The observation of this study helps to understand the genotype distribution of PCV2 and stands as a reference for future molecular epidemiological studies in North-eastern India.

Kinetic analysis of pathogenicity and tissue tropism of gyrovirus 3 in experimentally infected chickens.

Gyrovirus 3 (GyV3), the third novel emerging species of the genus Gyrovirus of the Anelloviridae family, has been described in multiple hosts. Epidemiologically, there are suggestions that GyV3 is associated with diarrhea/proventriculitis, however, no direct causal evidence exists between GyV3 infection and specific clinical diseases. Herein, we infected special pathogen-free (SPF) chickens with GyV3, and then assessed the pathogenicity and tissue tropism. The results revealed that GyV3 induced persistent infection characterized by diarrhea, aplastic anemia, immunosuppression, and persistent systemic lymphocytic inflammation. Clinically, the infected chickens presented ruffled feathers, diarrhea, anemia, and weight loss. Aplastic anemia was characterized by progressive depletion of hematopoietic cells in the bone marrow, immunosuppression was associated with atrophy of the thymus, spleen, and bursa of Fabricious, progressive lymphocytic inflammations were characterized by proventriculitis, adrenalitis, pancreatitis, hepatitis, nephritis, and bronchitis. Viral loads of GyV3 in tissues exhibited "M", "N", "W" or "V" type dynamic changes. The highest level of viral loads was reported in bone marrow at 7dpi, followed by the adrenal gland at 2 dpi, the sciatic nerve at 7 dpi, and bile at 35 dpi. The bone marrow and kidney demonstrate the strongest immunostaining of GyV3-VP1 antigen and were suggested as the target tissues of GyV3. Collectively, GyV3 is an immunosuppressive pathogenic virus that targets the bone marrow and kidney in chickens. Exploring the pathogenicity and tissue tropism of GyV3 will guide the basic understanding of the biology of GyV3 and its pathogenesis in chickens.

Mutation of the sixth amino acid of the Rep protein has no effect on porcine circovirus 2b but enhances porcine circovirus 2d replication in vitro.

Porcine circovirus type 2 (PCV2) is the etiological agent of post-weaning multisystemic wasting syndrome (PMWS). The original prevalent genotype, PCV2a, has been replaced by genotypes 2b and 2d in the swine population worldwide. The Rep protein is critical for viral replication. Comparison of a large number of Rep protein amino acid (aa) sequences showed that three sites distinguish genotype 2b from genotype 2d. In order to analyze the effect of exchanging the amino acids (asparagine and serine) at position 6 in the Rep proteins of PCV2b and PCV2d, two wild-type and two mutant viruses were rescued. Real-time quantitative PCR and a one-step growth curve were used to determine the viral load to assess the replication ability of the rescued viruses. The results showed that there was no significant difference in in vitro performance between the wild-type PCV2b and the mutated virus, while the mutation of PCV2d enhanced viral replication.

Identification of a novel circovirus in blood sample of giant pandas (Ailuropoda melanoleuca).

The members of the family Circoviridae are considered to be one of the smallest autonomously replicating viruses that are classified into two genera, Circovirus and Cyclovirus. Circoviruses have been found in a variety of vertebrates, but whether they infect endangered protected animals has not been studied in much detail. Here, viral metagenomics and PCR methods were used to detect and verify viral nucleic acid in the blood sample from giant pandas. According to these methods, the complete genome sequence of a novel circovirus, the giant panda associated circovirus (GPCV) from the blood sample of three giant pandas was identified. The GPCV genome is 2090 bp in size and reveals two putative ambisense open-reading frames, encoding the major structural capsid protein and the replication associated protein, respectively, the latter having two predicted introns. Pairwise sequence comparison and phylogenetic analyses indicated GPCV was a putative new species within genus Circovirus based on the species demarcation criteria of the International Committee on the Taxonomy of Viruses. It is the first time that circovirus has been identified from blood sample of giant pandas. These efforts will contribute to future analyses to illuminate the evolutionary relationships between classified and newly identified members of the family Circoviridae.

Viruses Infecting the European Catfish (Silurus glanis).

In aquaculture, disease management and pathogen control are key for a successful fish farming industry. In past years, European catfish farming has been flourishing. However, devastating fish pathogens including limiting fish viruses are considered a big threat to further expanding of the industry. Even though mainly the ranavirus (Iridoviridea) and circovirus (Circoviridea) infections are considered well- described in European catfish, more other agents including herpes-, rhabdo or papillomaviruses are also observed in the tissues of catfish with or without any symptoms. The etiological role of these viruses has been unclear until now. Hence, there is a requisite for more detailed information about the latter and the development of preventive and therapeutic approaches to complete them. In this review, we summarize recent knowledge about viruses that affect the European catfish and describe their origin, distribution, molecular characterisation, and phylogenetic classification. We also highlight the knowledge gaps, which need more in-depth investigations in the future.

Circoviruses and cycloviruses identified in Weddell seal fecal samples from McMurdo Sound, Antarctica.

Circoviridae is a family of circular single-stranded DNA viruses whose members infect a wide variety of hosts. While well characterized in avian and mammalian hosts, little is known about circoviruses associated with Antarctic animals. From 48 Weddell seal (Leptonychotes weddellii) fecal samples collected on the sea ice in McMurdo between Nov 2014 and Dec 2014, we identified and determined the genomes of novel viruses that fall within two genera of the family Circoviridae, i.e. Circovirus (n = 7) and Cyclovirus (n = 45). We named these viruses as werosea circovirus (WerCV) and werosea cyclovirus (WerCyV). The genomes of WerCV and WerCyV share ~63-64% genome-wide pairwise identity with classified circoviruses and cycloviruses, respectively. Based on the species demarcation threshold of 80% for members of the Circoviridae, the genomes of WerCV and WerCyV represent new species in their respective genera. Evidence indicated recombination in five of the 45 WerCyV genomes identified in this study. These are the first circoviruses found associated with Antarctic pinnipeds, adding to those recently identified associated with Adélie (Pygoscelis adeliae) and chinstrap penguins (P. antarcticus).

First detection and phylogenetic analysis of porcine circovirus 3 in female donkeys with reproductive disorders.

BACKGROUND: PCV3 is a pathogen associated with porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, and cardiac and multiorgan inflammation, which was newly identified in 2016 in sows in USA. Recently, PCV3 has also been identified from several non-porcine species like (cattle, dog, wild boar, deer, mice and ticks). However, PCV3 infection in donkey is not well established. Since 2019, 300 blood samples were collected from female donkey, which was characterized by abortion and sterility, in Liaocheng city of China. RESULTS: In the present study, an investigation of PCV3 in donkey blood samples was undertaken employing by real time PCR. Positive rates of PCV3 in donkeys reach to 21.0 %. In addition, one full-length PCV3 genome sequence was obtained, and it had a highest identity with porcine circovirus 3 PCV3/CN/Nanjing2017 strain and is clustered to PCV3a genotype based on ORF2 sequences. CONCLUSIONS: This is the first report of detection of PCV3 from female donkeys presenting reproductive failure in large-scale donkey farms, China. In addition, the PCV3 strain identified in this study shared the closest relationship with those from porcine, suggesting that PCV3 may be transmitted from pigs to donkeys. Totally, PCV3 infection in donkey should be concerned although the association between it and reproductive failure are not better understood.

Cross-species pathogenicity of gyrovirus 3 in experimentally infected chickens and mice.

Gyrovirus 3 (GyV3) has been identified in humans and other hosts, suggesting its cross-species pathogenicity, which poses an increased public health risk. In the current study, we established chicken and mouse models of GyV3 infection. We found that GyV3 induced persistent infections, characterized by viremia, aplastic anemia, immunosuppression, and systematic lymphocytic inflammation, in both species. Kinetic viral loads and antigen expression demonstrated rapid viral replication and broad tissue tropism of GyV3 in both models. The highest viral loads and the strongest antigen immunostaining were present in bone marrow and cerebrum in both chickens and mice, indicating that these are target tissues for GyV3. Genetic diversity analysis of VP1 in infected chickens and mice showed that GyV3 adapts to new hosts via rapid evolution of the hypervariable region of the gene encoding the structural protein VP1. Overall, our results indicate that GyV3 is a cross-species pathogenic virus; therefore, more attention needs to be paid to high levels of GyV3-induced neurotropism and aplastic anemia as a public health risk.

Detection of bat-associated circoviruses in Korean bats.

In recent years, several novel circular single-stranded DNA viruses have been detected in various mammals, birds, insects, and environmental samples using metagenomic and high-throughput sequencing approaches. In this study, we tested for the presence of circoviruses in 243 bat fecal samples collected between 2018 and 2019 from 48 sampling sites across Korea. To detect circoviruses, nested PCR was performed with degenerate primers targeting a conserved replication-associated protein (rep) gene of circovirus/cyclovirus. Among 243 samples tested, a total of 37 fecal samples from 14 sampling sites were PCR-positive for circoviruses at a frequency rate of 15.23%. We obtained 36 partial rep gene sequences of circoviruses and one complete genome sequence of bat-associated circovirus 12, encompassing a genome size of 2097 nt containing two inversely arranged open reading frames and a conserved nonamer sequence in the apex of a stem-loop structure. In addition, we found four bat species that were harboring circoviruses in Korea based on species identification PCR of circovirus-positive bat fecal samples. Detailed sequence analysis indicated that the bat-associated circovirus sequences identified in this study were related to those of known bat and avian groups of circoviruses. Herein, we report evidence for the presence of bat-associated circoviruses in Korean bats.

Macrophage Polarization Modulated by Porcine Circovirus Type 2 Facilitates Bacterial Coinfection.

Polarization of macrophages to different functional states is important for mounting responses against pathogen infections. Macrophages are the major target cells of porcine circovirus type 2 (PCV2), which is the primary causative agent of porcine circovirus-associated disease (PCVAD) leading to immense economic losses in the global swine industry. Clinically, PCV2 is often found to increase risk of other pathogenic infections yet the underlying mechanisms remain to be elusive. Here we found that PCV2 infection skewed macrophages toward a M1 status through reprogramming expression of a subset of M1-associated genes and M2-associated genes. Mechanistically, induction of M1-associated genes by PCV2 infection is dependent on activation of nuclear factor kappa B (NF-κB) and c-jun N-terminal kinase (JNK) signaling pathways whereas suppression of M2-associated genes by PCV2 is via inhibiting expression of jumonji domain containing-3 (JMJD3), a histone 3 Lys27 (H3K27) demethylase that regulates M2 activation of macrophages. Finally, we identified that PCV2 capsid protein (Cap) directly inhibits JMJD3 transcription to restrain expression of interferon regulatory factor (IRF4) that controls M2 macrophage polarization. Consequently, sustained infection of PCV2 facilitates bacterial infection in vitro. In summary, these findings showed that PCV2 infection functionally modulated M1 macrophage polarization via targeting canonical signals and epigenetic histone modification, which contributes to bacterial coinfection and virial pathogenesis.

Detection and molecular characterization of two canine circovirus genotypes co-circulating in Vietnam.

BACKGROUND: Canine circovirus is reported in dogs in many countries, including the USA, China and Thailand. It has been detected in healthy dogs and dogs with diarrhea, hemorrhagic gastroenteritis, and vasculitis. It comprises five genotypes and is frequently found as a coinfection with canine parvovirus-2 (CPV-2). AIM: To characterize canine circovirus genotypes co-circulating with CPV-2 in Vietnam. METHOD: PCR assessment of 81 CPV-2-positive fecal samples from Vietnamese diarrheic dogs up to seven months of age for other viral enteric pathogens, including canine bocavirus, canine adenovirus, paramyxovirus, canine coronavirus, porcine circovirus-3 and canine circovirus. In addition, eight selected full genome sequences of Vietnamese canine circovirus were analyzed and used for phylogeny. RESULTS: In total 19.8% of samples were found to be positive for canine circovirus. Phylogeny revealed that the Vietnamese canine circovirus strains were clustered in two different genotypes (genotype-1 and -3). The genetic diversity among Vietnamese canine circovirus was 86.0-87.2%. The nucleotide discrepancy among both genotypes altered the deduced amino acid sequence in 14 and ten residues of the replicase and capsid proteins, respectively. Genetic recombination analysis revealed that the Vietnamese canine circovirus-6 strain has the American and Chinese canine circovirus as its major and minor parents, respectively. Only a single dog revealed triple detections of CPV-2c, Canine circovirus and canine adenovirus (1.2%). CONCLUSION: The co-circulation of two different genotypes of canine circovirus and CPV-2c in dogs in Vietnam has been illustrated. CLINICAL RELEVANCE: The mortality rate with CPV-2 only (22%) doubled in dogs with canine circovirus and CPV-2 co-infection.

Pathogenic Characterization of a Porcine Circovirus Type 3 Isolate from Heilongjiang, China.

The clinical outcome of porcine circovirus 3 (PCV3) infection is still controversial. Herein, a novel PCV3 isolate (PCV3-China/DB-1/2017) with the molecular characterization of 24A and 27K in the Cap protein was used to inoculate three-week-old cesarean-derived, colostrum-deprived piglets. The nine PCV3 DB-1 inoculated piglets exhibited no obvious clinical symptoms or macroscopic lesions. PCV3 displayed a broad histotropism, including the heart, liver, spleen, lung, kidney, brain, lymph nodes, and tonsil, and the lungs and lymph nodes contained a higher quantity of viral genomes compared to that of the other organs. From 7 days after PCV3 DB-1 inoculation, the piglets showed obvious IgG antibody responses against PCV3 rCap-VLPs. The cumulative results demonstrated that PCV3 trend to low pathogenicity.

Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens.

Immunosuppression can increase the susceptibility of chickens to other disease-causing pathogens and interfere with the efficacy of vaccination against those pathogens. Chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) are common causes of immunosuppression in chickens. Immunosuppression was induced by experimental infection with either CAV or IBDV to assess the effect of immunosuppression on the efficacy of vaccination with Mycoplasma gallisepticum strain ts-304 against infection with virulent M. gallisepticum, a common bacterial pathogen of chickens worldwide. Birds were experimentally infected with either CAV or IBDV at 1 week of age, before vaccination and challenge with M. gallisepticum to examine the effect of immunosuppression at the time of vaccination, or at 6 weeks of age, after vaccination against M. gallisepticum but before challenge with virulent M. gallisepticum, to investigate the effect of immunosuppression at the time of challenge. All birds were vaccinated with a single dose of the ts-304 vaccine at 3 weeks of age and experimentally challenged with the virulent M. gallisepticum strain Ap3AS at 8 weeks of age. In immunosuppressed chickens there was a reduction in protection offered by the ts-304 vaccine at two weeks after challenge, as measured by tracheal mucosal thicknesses, serum antibody levels against M. gallisepticum, air sac lesion scores and virulent M. gallisepticum load in the trachea. Immunosuppressed birds with detectable serum antibodies against M. gallisepticum were less likely to have tracheal lesions. This study has shown that immunosuppression caused by infection with CAV or IBDV can interfere with vaccination against mycoplasmosis in chickens.

Prevalence and genetic analysis of porcine circovirus type 2 (PCV2) and type 3 (PCV3) between 2018 and 2020 in central China.

Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus-associated diseases (PCVAD), causing substantial economic losses to the swine industry worldwide. PCV3, as a recently discovered virus, is associated with porcine dermatitis, nephropathy syndrome, reproductive failure, congenital tremors, and other clinical symptoms. To further investigate the epidemic profile and genetic diversity of the two viruses, a total of 198 samples from swine at various growth stages suspected for PCVAD on 55 different pig farms between 2018 and 2020 were analyzed for presence of PCV2 and PCV3 by using a multiplex real-time PCR assay. Among the 198 samples, 113 (57.07%) and 72 (36.36%) were positive for PCV2 and PCV3 respectively, and 39 (19.7%) were positive for PCV2 and PCV3 co-infection. Subsequently, whole genome sequences of 34 PCV2 and 19 PCV3 strains were obtained from 30 and 19 clinical samples, respectively. Of these, 8 PCV2 strains belonged to PCV2a, 10 belonged to PCV2b and 16 belonged to PCV2d, indicating PCV2d was the predominant PCV2 genotype circulating in central China. Furthermore, co-infection of different PCV2 genotype strains was identified in three samples (JZ-4, KF-2 and JY-1), and a cross-recombination was found in the ORF2 region of the sequenced 13 PCV2d strains whose putative parental strains were LN6/1999 (MF278777) and MEX/41238/2014 (KT795287) strains. The phylogenetic analysis of PCV3 showed high nucleotide identity (>98%) among sequences obtained in this study and reference sequences. These data will aid our understanding of the molecular epidemiology and evolution of PCV2 and PCV3.