Pathogenesis of duck circovirus genotype 1 in experimentally infected Pekin ducks

Pathogenicity of duck circovirus and novel goose parvovirus co-infection in SPF ducks

Duck circovirus (DuCV) is one of the most prevalent infectious viruses in the duck industry in China. Although the clinical signs vary, it often causes immunosuppression in the host and leads to secondary infection with other pathogens. Novel goose parvovirus (NGPV) mainly infects ducks and causes short beak and dwarfism syndrome in ducks. However, the incidence of infection in ducks has increased in recent years, and the phenomenon of mixed infection with DuCV is common, resulting in more severe clinical morbidity. However, there are no systematic studies evaluating the presence of mixed infections. In order to investigate the synergistic pathogenicity of DuCV and NGPV co-infection in SPF ducks, a comparative experiment using DuCV and NGPV co-infection and mono-infection bird models was established. The results showed that the clinical signs of short beak, dwarfism and immunosuppression were more obvious in DuCV and NGPV co-infected ducks; the tissue damage of target organs was more serious, and the viral titre in organs and cloacal swabs were more significant compared with those of SPF ducks infected with only one virus. The results indicated that co-infection with DuCV and NGPV could promote viral replication and cause more severe tissue damage and immunosuppression than single virus infection. The present study reveals that the co-infection of NGPV and DuCV has a synergistic pathogenic effect from the aspect of pathogenicity, and the conclusions drawn not only clarify the direction of the subsequent research on the mechanism of co-infection of NGPV and DuCV, but also provide a scientific basis for the research on the co-infection of immunosuppressive pathogens and other pathogens.

Study on the infection characteristics and pathogenesis of duck circovirus 1 in Cherry Valley meat ducks

Duck circovirus (DuCV) infected multiple breeds of ducks and was widespread in duck factories worldwide. Infected ducks exhibited feathering disorder, growth retardation and immunosuppression, which lead to secondary infection with other pathogens easily. But till now, there has been little research on the study of DuCV due to the absence of appropriate cultural measures. This study developed an animal model to investigate the pathogenesis of DuCV-1 in vivo by infecting 84 one-day-old Cherry Valley meat ducklings. At 1, 3, 7, 14, 21, 28 and 35 days post-infection (DPI), six Cherry Valley meat ducks were randomly chosen to detect some indexes. The results showed that ducks infected with DuCV-1 exhibited depression, feather disorders and gained weight slowly. DuCV-1 was detected in serum, cloacal swabs, and throat swabs at 1 DPI and sustained during the experimental period. The contents of calcium, phosphorus and lymphocytes decreased while alanine aminotransferase and total bilirubin increased in the serum of sick ducks. DuCV-1 was detectable in all organs and caused multiple local lesions. The virus was initially detected in the liver and the organ with the highest viral titer was the thymus. Besides, immune organ indexes were significantly decreased. These results demonstrated that DuCV-1 could be transmitted horizontally and cause infection persistently. It possesses broad tissue tropism, damaging immune organs and potentially inducing immune suppression. This study could provide references for future research on the pathogenic mechanism of DuCV.

Epidemiological Investigation and Genetic Analysis of Duck Circovirus in Korea from 2013 to 2022

Duck circovirus (DuCV) infections cause immunosuppression in ducks, potentially leading to significant economic losses for the duck farming industry. This study investigates the prevalence, genetic characteristics, and evolutionary trends of DuCV in Korea between 2013 and 2022. Samples from 184 farms across seven provinces were analyzed using polymerase chain reaction (PCR). The overall DuCV infection rate was 29.4% (54/184), with Jeollanam-do showing the highest prevalence (37.5%, 15/40). Ducks aged 3-6 weeks were most susceptible to infection, while ducklings younger than one week were rarely infected. Whole-genome sequencing was performed on 24 positive samples with phylogenetic analysis revealing that DuCV-1b is the predominant subtype in Korea (23/24 strains). Notably, a Korean DuCV-1a subtype strain was identified for the first time, showing close genetic relatedness to Chinese DuCV 1a strains. Novel subtype-specific amino acid variations in ORF1 and ORF2 were statistically analyzed and classified. Recombination analysis suggested some Korean DuCV-1b strains may have resulted from recombination events involving strains from different countries. This comprehensive study provides crucial insights into the current prevalence, genetic diversity, and evolutionary dynamics of DuCV in Korea, offering valuable data for developing effective control strategies and understanding the global epidemiology of this economically important avian pathogen.

Genetic heterogeneity of duck circovirus first detected in geese from China

Duck circovirus (DuCV) can infect domestic and wild ducks, retarding growth and suppressing immunity, thereby increasing the possibility of secondary infection by other pathogens. In this study, for the first time, 2 DuCV strains (G221116 and G210917) were identified in geese from China. To study the genetic characteristics of the 2 goose-originated DuCVs, multiple sequence alignment and phylogenetic analyses were perforemed according to genome sequences of 2 DuCV strains g and reference waterfowl circoviruses retrieved from the GenBank database. Pairwise analysis showed that the genome sequence identities between the 2 DuCVs with reference DuCV-1 and DuCV-2 strains were 80.95% to 98.24%, and 58.04% to 59.55% with Goose circovirus (GoCV). Phylogenetic analysis showed that the 2 DuCVs belonged to DuCV-1 and DuCV-2 genotypes. These results broaden our understanding of the genetic heterogeneity and evolution of DuCV and suggest trans-host transmission of DuCV between ducks and geese.

Duck circovirus regulates the expression of duck CLDN2 protein by activating the MAPK-ERK pathway to affect its adhesion and infection

Duck circovirus (DuCV) is widely recognized as a prominent virus in China's duck farming industry, known for its ability to cause persistent infections and significant immunosuppression, which can lead to an increased susceptibility to secondary infections, posing a significant threat to the duck industry. Moreover, clinical evidence also indicates the potential vertical transmission of the virus through duck embryos to subsequent generations of ducklings. However, the limited availability of suitable cell lines for in vitro cultivation of DuCV has hindered further investigation into the molecular mechanisms underlying its infection and pathogenicity. In this study, we observed that oral DuCV infection in female breeding ducks can lead to oviduct, ovarian, and follicular infections. Subsequently, the infection can be transmitted to the fertilized eggs, resulting in the emergence of virus-carrying ducklings upon hatching. In contrast, the reproductive organs of male breeding ducks were unaffected by the virus, thus confirming that vertical transmission of DuCV primarily occurs through infection in female breeding ducks. By analyzing transcriptome sequencing data from the oviduct, we focused on claudin-2, a gene encoding the tight junction protein CLDN2 located on the cell membrane, which showed significantly increased expression in DuCV-infected oviducts of female breeding ducks. Notably, CLDN2 was confirmed to interact with the unique structural protein of DuCV, namely capsid protein (Cap), through a series of experimental approaches including co-immunoprecipitation (co-IP), GST pull-down, immunofluorescence, and adhesion-blocking assays. Furthermore, we demonstrated that the Cap protein binds to the extracellular loop structural domains EL1 and EL2 of CLDN2. Subsequently, by constructing a series of truncated bodies of the CLDN2 promoter region, we identified the transcription factor SP5 for CLDN2. Moreover, we found that DuCV infection triggers the activation of the MAPK-ERK signaling pathway in DEF cells and ducks, leading to an upregulation of SP5 and CLDN2 expression. This process ultimately leads to the transportation of mature CLDN2 to the cell surface, thereby facilitating increased virus adherence to the target organs. In conclusion, we discovered that DuCV utilizes host CLDN2 proteins to enhance adhesion and infection in oviducts and other target organs. Furthermore, we elucidated the signaling pathways involved in the interaction between DuCV Cap proteins and CLDN2, which provides valuable insights into the molecular mechanism underlying DuCV's infection and vertical transmission.

IMPORTANCE

Although duck circovirus (DuCV) poses a widespread infection and a serious hazard to the duck industry, the molecular mechanisms underlying DuCV infection and transmission remain elusive. We initially demonstrated vertical transmission of DuCV through female breeding ducks by simulating natural infection. Furthermore, a differentially expressed membrane protein CLDN2 was identified on the DuCV-infected oviduct of female ducks, and its extracellular loop structural domains EL1 and EL2 were identified as the interaction sites of DuCV Cap proteins. Moreover, the binding of DuCV Cap to CLDN2 triggered the intracellular MAPK-ERK pathway and activated the downstream transcription factor SP5. Importantly, we demonstrated that intracellular Cap also interacts with SP5, leading to upregulation of CLDN2 transcription and facilitating enhanced adherence of DuCV to target tissue, thereby promoting viral infection and transmission. Our study sheds light on the molecular mechanisms underlying vertical transmission of DuCV, highlighting CLDN2 as a promising target for drug development against DuCV infection.

Establishment and Application of Mismatch Amplification Mutation Assay-PCR for Rapid Detection and Differentiation of Duck Hepatitis A Virus-1 Attenuated Vaccine and Wild Strains

Duck hepatitis A virus type 1 (DHAV-1) is the main pathogen causing viral hepatitis in ducks, marked by high contagion and acute mortality. Live attenuated DHAV-1 vaccines are widely used to control the disease. This study aims to develop a mismatch amplification mutation assay (MAMA)-PCR for the rapid detection and differentiation of Korean DHAV-1 wild-type strains from vaccine strains. A MAMA primer was designed to target a single nucleotide polymorphism (SNPs) at position 2276 within the VP1 gene, allowing differentiation in a single PCR reaction. The MAMA-PCR accurately identified both strains, with detection limits of 100.5 ELD50/mL and 102.3 ELD50/mL, respectively. The MAMA-PCR demonstrated specificity, showing no cross-reactivity with 12 other viral and bacterial pathogens. The MAMA-PCR was applied to 89 farms, yielding results consistent with nested-PCR and sequence determination, identifying four positive farms for DHAV-1 vaccine strains. In conclusion, this study is the first to employ the MAMA-PCR method to distinguish between DHAV-1 wild-type and vaccine strains. The developed method is rapid, simple, specific, and sensitive, thereby serving as an effective tool for clinical diagnostics in identifying and differentiating between Korean DHAV-1 wild-type and vaccine strains.

Molecular genotyping and subgenotyping of duck circovirus at duck farms in Thailand

Background and Aim

Ducks worldwide are infected with duck circovirus (DuCV), which causes feather abnormality, emaciation, and poor growth performance. DuCV is similar to other circoviruses that induce immunosuppression due to the occurrence of the bursae of Fabricius (BF) and spleen atrophies. In Thailand, retarded ducks with feather losses were submitted for disease investigation. The ducks presented low body weight gain, had small BF and spleens, and were consistent with duck-infected DuCV. Our study investigated the possibility of DuCV infection in duck flocks in Thailand. We also analyzed the genetic characteristics of the virus.

Materials and Methods

BF and spleen samples were collected from affected meat and layer ducks from six farms thought to have been infected with DuCV. These tissues were then subjected to histopathological examination and molecular identification using conventional polymerase chain reaction and nucleotide sequencing. To identify DuCV, phylogenetic trees were generated using MEGA version X software. Samples of tissues or swabs were collected to determine whether coinfections with bacteria and viruses existed.

Results

Phylogenetic analysis using the entire genome (1995-1996 bp) and cap gene (762 bp) revealed that the DuCV isolates circulating in Thailand belonged to DuCV genotype I, which was further subdivided into two sub-genotypes: sub-genotype I b and an unclassified sub-genotype based on reference sub-genotypes. Thai isolates have variations in 10 amino acid residues in the capsid protein. Ducks infected with Thai DuCV were also coinfected with Riemerella anatipestifer, Escherichia coli, Pasteurella multocida, duck viral enteritis, and duck Tembusu virus, which is consistent with previous DuCV infection studies.

Conclusion

Six DuCVs from ducks who were previously found to have feather loss, were underweight, had growth retardation, and had poor body condition were identified in this study as belonging to genotype I and constituting at least two sub-genotypes. Due to the immunosuppressive effects of DuCV, coinfection of bacterial and viral pathogens was typically observed in Thai DuCV-infected ducks.

First report of goose circovirus identified in ducks from China

Goose circovirus (GoCV) is a common pathogen that causes immunosuppression and promotes secondary infections with other infectious agents in geese worldwide. In the present study, we identified GoCV in 2 out of 93 duck flocks from China and successfully sequenced the complete genomes of 2 strains (AH22du and HN20du). The whole genome of the two strains shared a high identity of 90.5 to 98.63% with China GoCV reference, and low identity of 58.98% with DuCV reference, respectively. Phylogenetic tree constructed on the two and other genome sequences of GoCV revealed three main branches. Both strains sequenced in this study were distributed on different sub-branches with most other Chinese GoCV strains, and AH22du clustered into an independent sub-branch within the cluster. Recombination analysis predicted that HN20du might potentially recombine from the major parent of yk4 (Zhejiang Province, China, 2007) and minor parent of GD/YJ/g2 (Guangdong Province, China, 2020). To the best of our knowledge, this is the first report of GoCV in ducks from China. This broadened host spectrum of GoCVs requires attention from the waterfowl industry and researchers.

Epidemiological investigation of fowl adenovirus (FAdV) infections in ducks and geese in Shandong Province, China

RESEARCH HIGHLIGHTS

Samples of suspected FAdV-infected waterfowl from farms in Shandong Province were collected from 2019 to 2022.Single infections with FAdV were less frequent than mixed infections.477 out of 792 samples (60.23%) tested positive for FAdV nucleic acids.Detection rate of FAdV was 65.47% in fattening duck farms, 55.73% in breeder duck farms and 54.55% in fattening geese farms.

Interactions between avian viruses and skin in farm birds

This article reviews the avian viruses that infect the skin of domestic farm birds of primary economic importance: chicken, duck, turkey, and goose. Many avian viruses (e.g., poxviruses, herpesviruses, Influenza viruses, retroviruses) leading to pathologies infect the skin and the appendages of these birds. Some of these viruses (e.g., Marek's disease virus, avian influenza viruses) have had and/or still have a devasting impact on the poultry economy. The skin tropism of these viruses is key to the pathology and virus life cycle, in particular for virus entry, shedding, and/or transmission. In addition, for some emergent arboviruses, such as flaviviruses, the skin is often the entry gate of the virus after mosquito bites, whether or not the host develops symptoms (e.g., West Nile virus). Various avian skin models, from primary cells to three-dimensional models, are currently available to better understand virus-skin interactions (such as replication, pathogenesis, cell response, and co-infection). These models may be key to finding solutions to prevent or halt viral infection in poultry.

Simultaneous detection and differentiation of DuCV-1 and DuCV-2 by high-resolution melting analysis

Birds infected with duck circovirus (DuCV) can potentially cause immunosuppression by damaging lymphoid tissues, causing great losses in the duck breeding industry. Duck circovirus can be divided into two genotypes (DuCV-1 and DuCV-2), but simultaneous detection and differentiation of DuCV-1 and DuCV-2 by high-resolution melting (HRM) analysis is still lacking. Here, we designed specific primers according to the sequence characteristics of the newly identified ORF3 gene and then established a PCR-HRM method for the simultaneous detection and differentiation of DuCV-1 and DuCV-2 via high-resolution melting analysis. Our data showed that the established PCR-HRM assay had the advantages of specificity, with the lowest detection limits of 61.9 copies/μL (for DuCV-1) and 60.6 copies/μL (for DuCV-2). The melting curve of the PCR-HRM results indicated that the amplification product was specific, with no cross-reaction with common waterfowl origin pathogens and a low coefficient of variation less than 1.50% in both intra-batch and inter-batch repetitions, indicating the advantages of repeatability. We found that the percentage of DuCV-2-positive ducks was higher than that of DuCV-1-positive ducks, with 8.62% rate of DuCV-1 and DuCV-2 coinfection. In addition, we found DuCV-2-positive in geese firstly. In conclusion, this study provides a candidate PCR-HRM assay for the detection and accurate differentiation of DuCV-1 and DuCV-2 infection, which will help us for further epidemiological surveillance of DuCVs.

Pathogenicity of duck circovirus 1 in experimentally infected specific pathogen-free ducks

Ducks infected with duck circovirus (DuCV) show symptoms such as feather loss, growth retardation and low body weight in the flock. The virus induces immunosuppression and increases the prevalence of infection with other pathogens. However, most studies on duck circovirus were focused on coinfection, and fewer studies had been conducted on the pathogenicity of duck circovirus alone. The aim of the present study was to investigate the pathogenesis of DuCV-1 in experimentally infected specific pathogen-free ducks. In this study, we sequenced the whole genome of a strain of duck circovirus and identified the virus genotype as DuCV-1b. This strain of duck circovirus was named SDLH(OR567883). Animal pathogenicity experiments were then conducted, wherein specific pathogen-free ducks were infected by mucosal injection and abdominal injection. Infected ducks were sampled for 4 consecutive weeks after infection and showed symptoms of dwarfism. We further examined the replication of DuCV-1 in the ducks. The highest virus titers in the 2 infection groups were found in the liver and spleen, with different results for the different routes of infection. Pathological sections of duck organs were made and it was found that organs such as the liver and spleen were damaged by DuCV-1. In conclusion, our experimental results indicate that DuCV-1 can infect ducks individually and cause widespread organ damage in infected ducks.

From obscurity to urgency: a comprehensive analysis of the rising threat of duck circovirus

Duck circovirus (DuCV) is a small, nonenveloped, single-stranded DNA virus with immunosuppressive effects on ducks that leads to slow growth and elevated mortality following mixed infections. Its infection manifests as feather loss, slow growth, swelling of respiratory tissue, and damage to immune organs in ducks. Although single infections with DuCV do not cause noticeable clinical symptoms, its ability to compromise the immune system and facilitate infections caused by other pathogens poses a serious threat to duck farming. Given the prevalence of this disease and the increasing infection rates in recent years, which have resulted in significant economic losses in duck farming and related sectors, research and control of DuCV infection have become especially important. The aim of this review is to provide a summary of the current understanding of DuCV, serving as a reference for subsequent research and effective control of the virus. We focus mainly on the genetics and molecular biology, epidemiology, clinical symptoms, and pathology of DuCV. Additionally, topics such as the isolation and culture of the virus, vaccines and antiviral therapies, diagnostics, and preventative measures are discussed.

Molecular Detection and Genetic Characterization of Vertically Transmitted Viruses in Ducks

To investigate the distribution and genetic variation in four vertically transmitted duck pathogens, including duck hepatitis B virus (DHBV), duck circovirus (DuCV), duck hepatitis A virus 3 (DHAV-3), and avian reoviruses (ARV), we conducted an epidemiology study using PCR and RT-PCR assays on a duck population. We found that DHBV was the most prevalent virus (69.74%), followed by DuCV (39.48%), and then ARV (19.92%) and DHAV-3 (8.49%). Among the 271 duck samples, two, three or four viruses were detected in the same samples, indicating that the coinfection of vertical transmission agents is common in ducks. The genetic analysis results showed that all four identified DuCV strains belonged to genotype 1, the DHAV-3 strain was closely clustered with previously identified strains from China, and the ARV stain was clustered under genotype 1. These indicate that different viral strains are circulating among the ducks. Our findings will improve the knowledge of the evolution of DuCV, DHAV-3, and ARV, and help choose suitable strains for vaccination.

Effect of duck interferon-α and an anti-cap protein polyclonal antibody against duck circovirus

Duck circovirus (DuCV) is one of the most prevalent viruses in the duck breeding industry, and causes persistent infection and severe immunosuppression. Currently, there is a serious lack of prevention and control measures and no commercial vaccine against DuCV. Therefore, effective antiviral drugs are important for treating DuCV infection. Interferon (IFN) is an important component of antiviral innate immunity, but it remains unclear whether duck IFN-α has a clinical effect against DuCV. Antibody therapy is an important way to treat viral infections. The DuCV structural protein (cap) is immunogenic, and it remains to be determined whether an anti-cap protein antibody can effectively block DuCV infection. In this study, the duck IFN-α gene and the DuCV structural protein cap gene were cloned, expressed and purified in Escherichia coli to prepare duck recombinant IFN-α and the cap protein. Then, rabbits were immunized with the recombinant cap protein to prepare a rabbit polyclonal antibody. This study investigated the antiviral effect of duck recombinant IFN-α and the anti-cap protein antibody and their combined effect on Cherry Valley ducks infected with DuCV. The results showed that the treatment significantly alleviated the clinical symptoms of immune organ atrophy and immunosuppression compared with the control. The histopathological damage of the target organs was alleviated, and replication of DuCV in the immune organs was significantly inhibited. The treatment also reduced the damage caused by DuCV to the liver and immune function, and increased the level of the DuCV antibody in the blood, thereby improving antiviral activity. Notably, the combination of duck IFN-α and the polyclonal antibody completely blocked DuCV infection after 13 days under the experimental conditions, showing a better inhibitory effect on DuCV infection than single treatments. These results showed that duck recombinant IFN-α and the anti-cap protein antibody can be used as antiviral drugs to clinically treat and control DuCV infection, particularly the vertical transmission of the virus in breeding ducks.

Canine circovirus among dogs and cats in China: first identification in cats

Canine circovirus (CanineCV) is a virus associated with respiratory and digestive diseases in dogs and often occurs in coinfections with other pathogens, thereby aggravating the symptoms of infected dogs. CanineCV was first reported in the United States in 2012. Subsequently, it was reported among dogs in Europe, Asia, and South America. To investigate the prevalence of CanineCV in dogs in China, 331 dog samples were collected in this study. The PCR results showed that 9.06% (30/331, 95% CI = 6.2% ~ 12.7%) of the dog samples were CanineCV positive. CanineCV has also been detected in some carnivorous wild animals, indicating the potential risk of cross-species transmission of this virus. And, cats are also one of the most common pets in our daily lives, who is close contact with dogs. Thus, this study first investigated the prevalence of CanineCV in cats. The PCR results showed that 3.42% (14/409, 95% CI = 1.9% ~ 5.7%) of the cat samples were CanineCV positive. Moreover, 14 canine-derived CanineCV whole genomes and the first cat-derived CanineCV whole genome were obtained in this study. Rep and Cap are the major nonstructural proteins and structural proteins of CanineCV, respectively. In nucleic acid homology analyses, these 15 CanineCV strains showed a high degree of variation in Rep (85.9 ~ 99%) and Cap (85.6 ~ 100%). In phylogenetic analyses, the 15 CanineCV strains clustered into 3 different genotypes (genotypes 1, 3, and 4). Among them, the first cat-derived CanineCV belonged to CanineCV-3. In addition, 4 genetic recombination events were predicted in these 15 CanineCV strains, occurring in multiple regions of the genome. In conclusion, this study is the first to provide evidence of CanineCV infection in cats and successfully obtained the first whole genome of cat-derived CanineCV. The complex circulation and high prevalence of CanineCV among dogs and cats emphasize the importance of continuous monitoring of this virus in various animal species.

Multiplex digital PCR: a superior technique to qPCR for the simultaneous detection of duck Tembusu virus, duck circovirus, and new duck reovirus

Duck Tembusu virus (DTMUV), duck circovirus (DuCV), and new duck reovirus (NDRV) have seriously hindered the development of the poultry industry in China. To detect the three pathogens simultaneously, a multiplex digital PCR (dPCR) was developed and compared with multiplex qPCR in this study. The multiplex dPCR was able to specifically detect DTMUV, DuCV, and NDRV but not amplify Muscovy duck reovirus (MDRV), Muscovy duck parvovirus (MDPV), goose parvovirus (GPV), H4 avian influenza virus (H4 AIV), H6 avian influenza virus (H6 AIV), and Newcastle disease virus (NDV). The standard curves showed excellent linearity in multiplex dPCR and qPCR and were positively correlated. The sensitivity results showed that the lowest detection limit of multiplex dPCR was 1.3 copies/μL, which was 10 times higher than that of multiplex qPCR. The reproducibility results showed that the intra- and interassay coefficients of variation were 0.06-1.94%. A total of 173 clinical samples were tested to assess the usefulness of the method; the positive detection rates for DTMUV, DuCV, and NDRV were 18.5, 29.5, and 14.5%, respectively, which were approximately 4% higher than those of multiplex qPCR, and the kappa values for the clinical detection results of multiplex dPCR and qPCR were 0.85, 0.89, and 0.86, indicating that the two methods were in excellent agreement.

Generation of a monoclonal antibody against duck circovirus capsid protein and its potential application for native viral antigen detection

Introduction

Duck circovirus (DuCV) infection is currently recognized as an important immunosuppressive disease in commercial duck flocks in China. Specific antibodies against DuCV viral proteins are required to improve diagnostic assays and understand the pathogenesis of DuCV infection.

Methods and results

To generate DuCV-specific monoclonal antibodies (mAbs), a recombinant DuCV capsid protein without the first 36 N-terminal amino acids was produced in Escherichia coli. Using the recombinant protein as an immunogen, a mAb was developed that reacted specifically with the DuCV capsid protein, expressed in E. coli and baculovirus systems. Using homology modeling and recombinant truncated capsid proteins, the antibody-binding epitope was mapped within the region of ¹⁴⁴IDKDGQIV¹⁵¹, which is exposed to solvent in the virion capsid model structure. To assess the applicability of the mAb to probe the native virus antigen, the murine macrophage cell line RAW267.4 was tested for DuCV replicative permissiveness. Immunofluorescence and Western blot analysis revealed that the mAb recognized the virus in infected cells and the viral antigen in tissue samples collected from clinically infected ducks.

Discussion

This mAb, combined with the in vitro culturing method, would have widespread applications in diagnosing and investigating DuCV pathogenesis.

Pathogenicity of duck circovirus and fowl adenovirus serotype 4 co-infection in Cherry Valley ducks

Duck circovirus (DuCV) is one of the most prevalent infectious viruses in the duck industry in China. Although the clinical symptoms vary, it often causes immunosuppression in the host and leads to secondary infection with other pathogens. Fowl adenovirus serotype 4 (FAdV-4) mainly infects chickens and causes hydropericardium hepatitis syndrome. However, the incidence of infection in ducks has increased in recent years, and the phenomenon of mixed infection with DuCV is very common, resulting in more severe clinical morbidity. However, there is no systematic study evaluating the presence of mixed infection. To explore the synergistic pathogenicity of DuCV and FAdV-4 co-infection in Cherry Valley ducks, a comparative experiment was established between DuCV and FAdV-4 co-infection and single infection animal models. It was found that DuCV and FAdV-4 co-infected ducks showed more pronounced clinical signs of pericardial effusion, hepatitis and immunosuppression; more severe tissue damage in target organs; and more significant levels of viral load, biochemical indicators and immune indicators in various organs compared with Cherry Valley ducks infected with just one virus. The results showed that co-infection with DuCV and FAdV-4 may promote greater viral replication, causing more severe tissue damage and immunosuppression than infection with just one virus. Therefore, the monitoring and prevention of the two viruses should be strengthened clinically, with a particular focus on the potential harm of DuCV as it carries the highest infection rate.

Development and application of a multiplex qPCR assay for the detection of duck circovirus, duck Tembusu virus, Muscovy duck reovirus, and new duck reovirus

A multiplex qPCR assay was developed to simultaneously detect duck circovirus (DuCV), duck Tembusu virus (DTMUV), Muscovy duck reovirus (MDRV), and novel duck reovirus (NDRV), but it did not amplify other viruses, including duck virus enteritis (DVE), infectious bursal disease virus (IBDV), avian reovirus (ARV), H5 avian influenza virus (H5 AIV), H7 avian influenza virus (H7 AIV), H9 avian influenza virus (H9 AIV), Newcastle disease virus (NDV), and Muscovy duck parvovirus (MDPV), and the detection limit for DuCV, DTMUV, MDRV, and NDRV was 1.51 × 10¹ copies/μL. The intra- and interassay coefficients of variation were less than 1.54% in the repeatability test with standard plasmid concentrations of 1.51 × 10⁷, 1.51 × 10⁵, and 1.51 × 10³ copies/μL. The developed multiple qPCR assay was used to examine 404 clinical samples to verify its practicability. The positivity rates for DuCV, DTMUV, MDRV, and NDRV were 26.0%, 9.9%, 4.0%, and 4.7%, respectively, and the mixed infection rates for DuCV + DTMUV, DuCV + MDRV, DuCV + NDRV, MDRV + NDRV, DTMUV + MDRV, and DTMUV + NDRV were 2.7%, 1.2%, 1.2%, 1.0%, 0.5%, and 0.7%, respectively.

Effect of Echinacea on gut microbiota of immunosuppressed ducks

Introduction

Immunosuppression puts animals in a susceptible state and disrupts the balance of intestinal flora, which can increase the risk of disease and cause serious harm to the farm. Echinacea can exert its immunomodulatory effect in various ways, but its influence on intestinal flora is unclear.

Methods

Therefore, we investigated the effect of Echinacea extract (EE) on gut microbiota in immunosuppressed ducks by 16s-RNA sequencing in this experiment.

Results

The results showed that EE significantly improved the weight gain of immunosuppressed ducks (p<0.001). It also increased the immune organ index (p<0.01) and upregulated the levels of TNF-α and IFN-γ (p<0.05) as well as IL-2 in the serum. The lesions of the bursa were evident compared to the spleen and thymus. After treatment in the EE group, the lymphocyte count of the bursa returned to healthy levels and the lesions were significantly improved. The diversity analysis showed that neither of the alpha-diversity indices showed a significant difference (p>0.05). However, the EE group had a trend closer to the healthy group compared to the M group. β-diversity analysis revealed a high degree of sample separation between the healthy and immunosuppressed groups. The sequencing result showed a significantly higher relative abundance of Prevotella and Prevotella_UCG_001 in the dexamethasone-treated group, which could be potential biomarkers of dexamethasone-induced immunosuppression. EE increased the relative abundance of Akkermansia, Bacteroides, and Alistipes and significantly decreased the relative abundance of Megamonas, Streptococcus, and Enterococcus (p<0.05).

Conclusion

The results showed that Echinacea extract improves the development of immunosuppressed ducks and modulates intestinal immune function by increasing the abundance of beneficial bacterial genera in the intestine.

Evaluation of the antiviral effect of four plant polysaccharides against duck circovirus

Recently, outbreaks of duck circovirus (DuCV) are frequently occurring worldwide due to secondary infections caused by post infection-induced immunosuppression. Due to a lack of preventive drugs and vaccines, the waterfowl industry losses are ever increasing. In this study, we extracted Astragalus polysaccharides (APS), pine pollen polysaccharides (PPPS), Aloe vera polysaccharides (AVE), and Ficus carica polysaccharides (FCPS) from Astragalus, pine pollen, aloe, and F. carica leaves, respectively. We randomly divided 150 one-day-old Cherry Valley ducks into five groups, which were inoculated with the DuCV solution and orally administered APS, PPPS, AVE, FCPS, and phosphate buffer saline (PBS), respectively. We collected the duck immune organs and serum samples at 8, 16, 24, 32, 40, and 48 days post-infection (dpi). Using clinical symptom analysis, molecular biology experiments, and serological experiments, we proved that plant polysaccharides could (a) improve the duck immunity, (b) reduce the viral load, and (c) mitigate DuCV-induced damage to immune organs, with both APS and PPPS having significant effects. Moreover, we detected viral load and cytokines within the first 8 dpi. Since the body's innate immunity could inhibit viral replication within five days of virus infection, 1-5 dpi was the best treatment time. Among the four polysaccharides showing in vitro anti-apoptotic activity, APS and PPPS significantly inhibited the DuCV infection-induced apoptosis of peripheral blood lymphocytes. Overall, since our findings show APS and PPPS having significant anti-DuCV effects both in vivo and in vitro, they can be promising candidates for preventing DuCV infection in ducks.

Epidemiology, genetic diversity, and association of canine circovirus infection in dogs with respiratory disease

Although canine circovirus (CanineCV)-associated with gastroenteritis has been well documented, the virus is also detectable in the respiratory discharge of dogs with respiratory disease. In this study, an epidemiological approach was used to explore the association between the presence of CanineCV and respiratory symptoms in dogs. Respiratory swabs were collected from 76 healthy dogs and 114 dogs with respiratory illness and tested for CanineCV using conventional PCR (cPCR). Furthermore, lung tissues collected from 15 necropsied dogs showing pneumonia were tested using the real-time PCR (qPCR) and in situ hybridization (ISH) technique. A total of 8.95% (17/190) of dogs were CanineCV positive, with a significant association (p = 0.013) in dogs with respiratory signs. Four necropsied dogs were qPCR positive with the CanineCV-DNA labeling localized in tracheobronchial lymphoid cells (3/4), pulmonary parenchyma, capillary endothelia, and mononuclear cells harboring in alveoli (2/4). Full-length genome sequences of seven CanineCV strains were analyzed, indicating that the detected CanineCV genome clustered in the CanineCV-4 genotype. Genetic recombination was also evident in the replicase (Rep) gene. Although the role of CanineCV primarily affecting lung lesions could not be determined from this study, the presence of CanineCV DNA in pulmonary-associated cells indicated the potential association of the virus with canine respiratory disease; thus, linking causality must be examined in further studies.

Effects of duck circovirus on immune function and secondary infection of Avian Pathogenic Escherichia coli

Duck circovirus (DuCV) infection occurs frequently in ducks in China and is generally believed to lead to immunosuppression and secondary infection, though there has been a lack of detailed research and direct evidence. In this study, one-day-old Cherry Valley ducklings were artificially infected with DuCV alone and co-infected with DuCV and Avian Pathogenic Escherichia coli (APEC). The immune indexes at 32 d old were systematically monitored, including immune organ weight, lymphocyte transformation rate, IL-10, IL-12, soluble CD4 (sCD4), soluble CD8 (sCD8), IFN-γ, viral loads in each organ, APEC colonization, and so on. The results showed the development of immune organs in ducklings was affected, resulting in a decrease in the lymphocyte transformation rate (LTR), IL-12, sCD4, sCD8, IFN-γ and an increase in IL-10 content at 8 to 32 d postinfection (dpi). In the detection of virus loads in some organs, it was found that 8 dpi, DuCV existed stably in various organs, suggesting the importance of preventing and controlling the virus in the early stage of culture. The results of exploring the DuCV infection that shows some influence on secondary infection by APEC. The results showed that DuCV infection could significantly enhance the pathogenicity of APEC and the colonization ability of APEC in vivo. DuCV can induce more serious APEC infection in 24 dpi than in 14 dpi. Based on the above results, it can be concluded that DuCV infection will affect the immune system, cause immunosuppression, and lead to more serious secondary infection.

Detection and Molecular Characterization of a Novel Species of Circovirus in a Tawny Owl (Strix aluco) in Southern Italy

Simple Summary

The genus Circovirus groups some of the smallest viruses capable of autonomous replication, including some notable swine and avian pathogens. Among domestic and wild birds, circoviruses are often associated with immunosuppression and integumental disorders, but, despite their relevance, nothing is known about their circulation in birds of prey. By conducting molecular analyses on samples from birds of prey recovered by a wildlife rescue centre in Italy, we identified a new viral species in the spleen of a tawny owl (Strix aluco). However, there is contrasting evidence regarding its definitive host. On one hand, the virus was discovered to be phylogenetically closer to mammalian rather than avian circoviruses, which allows speculations on its host being a micromammal preyed by the tawny owl, rather than the bird itself. On the other hand, its detection in the spleen, a lymphoid organ in which other avian circoviruses are often detected, supports the tawny owl being its actual host, perhaps following a spillover event associated with predation. Adding to the growing number of circoviruses found in recent years in a diverse range of hosts, this discovery represents another step forward in the characterization of this genus of remarkable veterinary importance.

Abstract

Thanks to recent developments in molecular methods, many new species have been discovered within the genus Circovirus, which comprises viruses of veterinary relevance found in a broad range of hosts. In particular, several circoviruses are known to infect birds, often causing immunosuppression and feathering disorders. Nonetheless, nothing is known about their circulation in birds of prey. In this study, samples from 61 birds of prey representing ten different species, recovered by a wildlife rescue centre in Southern Italy, were taken at necropsy and analysed by PCR with pan-Circovirus primers. Only one sample, collected from a tawny owl (Strix aluco), tested positive. Its genome, sequenced by primer walking, displays the typical features of circoviruses. Based on demarcation criteria, the detected strain qualifies as a novel species, which was named “tawny owl-associated circovirus” (ToCV). Phylogenetically, ToCV clustered with mammalian rather than avian circoviruses, and its closeness to a rodent circovirus suggests that its host may have been a micromammal eaten by the tawny owl. On the other hand, its detection in the spleen fits with the tropism of other avian circoviruses. Little can be therefore said on its biology and pathogenicity, and further efforts are needed to better characterize its epidemiology.

Development of a dual-labeled, hydrolysis probe-based, real-time quantitative PCR assay for detection of both genotypes of duck circovirus-1 (DuCV-1) and DuCV-2

In this study, we developed a real-time quantitative polymerase chain reaction (qPCR) assay based on a dual-labeled hydrolysis probe to simultaneously detect both duck circovirus (DuCV) 1 and DuCV-2. The reproducibility, sensitivity and specificity of the primer set and probe were evaluated using other duck pathogens. The detection limit was 20 copies per µL. The intra-assay coefficients of variation (CVs) were ≤ 0.73% and the inter-assay CVs were ≤ 1.89%. No cross-reaction occurred with other duck pathogens. In addition, the qPCR assay was successfully applied to the simultaneous detection of DuCV-1 and DuCV-2 in clinical field samples. Therefore, this assay will be useful for laboratory diagnosis and epidemiological field studies of DuCV.

Molecular characteristics of a novel duck circovirus subtype 1d emerging in Anhui, China

The frequency of infection of duck circovirus (DuCV) in Anhui province, China is not well-characterized. Therefore, in this study, we collected 69 samples from sick ducks and tested them for the presence of DuCV by conventional polymerase chain reaction (PCR) analysis. The complete viral genomes of five DuCV strains from five different cities were randomly selected, amplified via PCR, sequenced, and subjected to recombination analysis. The five DuCV genomes were named as AHAU9, AHAU25, AHAU28, AHAU37, and AHAUHQ. We found that 36.2 % of the ducks were infected with DuCV. The five DuCV strains had genome lengths ranging from 1987 to 1995 nucleotides, with a sequence similarity of 81.8-98.2 %. Among them, AHAU28, AHAU37, and AHAUHQ were closely related to the reference strain YF180403, GX1105 strain, and wd2015028 of DuCV, respectively. AHAU9 and AHAU25 were found to belong to a new DuCV subtype, DuCV-1d. Moreover, recombination analysis showed that the DuCV-1d subtype strains had the same recombination pattern. These results improve the understanding of the frequency of DuCV infection in Anhui province. Our findings may be useful for preventing and controlling the spread of DuCV.

Novel genotype definition and genome characteristics of duck circovirus in central and Eastern China

To explore genetic variations in duck circovirus (DuCV) and the molecular epidemiology of its infection, tissue samples were collected from 219 dead ducks from 20 farms in the central and eastern regions of China. All farms tested positive for DuCV, with duck-origin goose parvovirus, reovirus and Tembusu virus having co-infection rates of 100%, 0% and 0%, respectively. A total of 20 strains from the DuCV-positive flock were sequenced. The total sequence length was 1987-1996 nt, and the sequences shared 82% (JX499186, DuCV2 from Sichuan province, China) to 99.7% (KY328304, DuCV1 from Shandong Province, China) sequence identity with DuCV sequences available in GenBank. Hyper-variable regions were mainly located in open reading frame (ORF)2, ORF3 and intergenic regions. The tertiary structure of ORF2 from four provinces (Henan, Anhui, Zhejiang and Fujian) in China showed a canonical viral jelly roll and the antigenic epitope of ORF2 located in the bulge of the protein surface. Overall, 15 of the 20 DuCV strains are possibly derived through inter-genotypic and intragenotypic recombination. Based on sequence and phylogenetic analyses, six strains from Fujian Province clustered into a novel genotype-DuCV-1d. These findings may enrich our understanding of DuCV evolution and circulation and lay the foundation for vaccine strain selection.

Viral metagenomics in Brazilian Pekin ducks identifies two gyrovirus, including a new species, and the potentially pathogenic duck circovirus

Viral metagenomics coupled to high-throughput sequencing has provided a powerful tool for large-scale detection of known and unknown viruses associated to distinct hosts and environments. Using this approach, known and novel viruses have been characterized from sylvatic and commercial avian hosts, increasing our understanding of the viral diversity in these species. In the present work we applied an exploratory viral metagenomics on organs (spleen, liver and bursa of Fabricious) of Pekin ducks from Southern Brazil. The virome contained sequences related to a known duck pathogen (duck circovirus) and a number of other circular ssDNA viruses. Additionally, we detected avian gyrovirus 9 (to date detected only in human feces) and one new avian gyrovirus species, to which is proposed the name avian gyrovirus 13 (GyV13). This study is expected to contribute to the knowledge of the viral diversity in Pekin ducks.

Coinfection of novel goose parvovirus-associated virus and duck circovirus in feather sacs of Cherry Valley ducks with feather shedding syndrome

Since 2017, an infectious disease, named feather shedding syndrome (FSS), has consistently broken out in Cherry Valley ducks in East China. The sick ducks showed the new clinical symptoms of feather shedding and being plucked off with difficulty after slaughter. The high incidence rate of 20 to 70% predominantly happened in ducks of 4 to 5 wk of age, and nearly 40% mortality rate was observed in infected ducks. To explore the possible role of novel goose parvovirus–associated virus (NGPV) and duck circovirus (DuCV) in this disease, a total of 540 feather sac samples were collected from sick ducks with FSS. The infection rates of NGPV and DuCV in samples were 82.78 and 78.89%, respectively, and the coinfection rate of the 2 viruses was 70.00%. Notably, ducks of 4 to 5 wk of age usually presented obvious and severe FSS in the flocks with high codetection rate of NGPV and DuCV. Furthermore, 9 NGPV strains were isolated from feather sacs and 5 synchronous amino acid mutations were demonstrated in VP3 protein. These results indicated that coinfection of NGPV and DuCV might play an important role in duck FSS disease.

Evaluation of a novel inactivated vaccine against duck circovirus in muscovy ducks

Duck circovirus (DuCV), an immunosuppressive pathogen, causes serious damage to waterfowls worldwide. A highly efficient vaccine would play a crucial role in preventing DuCV infections in the waterfowl breeding industry. However, to date, there is a dearth of commercial vaccines owing to the lack of a cell culture system for propagating the requisite virus amounts in vitro. In this study, we isolated DuCVs from Muscovy ducks, helped them proliferate using peripheral blood mononuclear cells (PBMCs), and developed an inactivated vaccine. Muscovy ducks vaccinated with the inactivated vaccine had higher neutralizing antibody titers than the control ducks and higher protection in the challenge experiment (as assessed by weight measurement). Moreover, the inactivated vaccine did not cause feather abnormalities, growth repression, and dwarf syndrome; likewise, lesions and lymphocyte apoptosis in the bursa of Fabricius, spleen, and thymus were not observed. Significantly lower virus shedding from the inactivated vaccine was detected up to 42 days post-inoculation. Together, these results suggest that the inactivated DuCV vaccine can induce a high immune response, is relatively safer for Muscovy ducks, and thus it is a protective vaccine candidates against DuCV infection.

Comparative pathogenicity of two subtypes (hepatitis-type and pancreatitis-type) of duck hepatitis A virus type 1 in experimentally infected Muscovy ducklings

Duck hepatitis A virus type 1 (DHAV-1) causes acute hepatitis with high morbidity and mortality in ducklings of the genera Cairina and Anas and is characterized by ecchymotic haemorrhage and necrosis of the liver surface. Since September 2011, a new subtype of DHAV-1 (named pancreatitis-type DHAV-1) has been isolated. This new subtype is characterized by yellowish or haemorrhagic pancreatitis, but with no significant pathological changes in the liver. To further investigate the difference in pathogenicity between hepatitis-type DHAV-1 and pancreatitis-type DHAV-1, we infected Muscovy ducklings with a hepatitis-type DHAV-1 strain, FZ86, or a pancreatitis-type DHAV-1 strain, MPZJ1206, and then compared the resulting gross lesions, histopathological changes, viral distribution and cellular apoptosis in the liver and pancreas of Muscovy ducklings. The results suggested that FZ86 induced a more efficient viral propagation in the liver than MPZJ1206, and the gross and histopathological lesions were also limited to the liver. However, MPZJ1206 induced more effective viral replication in the pancreas than FZ86. The MPZJ1206-infected Muscovy ducklings showed an obviously yellowed and haemorrhagic pancreas, but with no significant pathological changes in the liver. Furthermore, FZ86 induced notable hepatocyte apoptosis and increased the expression of caspase-3 in the liver, whereas MPZJ1206 caused apoptosis in a large number of acinar epithelial cells and elevated the expression of caspase-3 in the pancreas. Taken together, these results demonstrated that pancreatitis-type DHAV-1 has many new pathogenic features which distinguish it from the hepatitis-type DHAV-1. RESEARCH HIGHLIGHTS Pancreatitis-type DHAV-1 (MPZJ1206) was characterized by pancreatic haemorrhage and yellow discolouration, but with no obvious haemorrhage and necrosis in the liver. Pancreatitis-type DHAV-1 (MPZJ1206) exhibits many new pathogenic features which distinguish it from the hepatitis-type DHAV-1 (FZ86).

Molecular detection and genomic characterization of porcine circovirus 3 in pigs from Northeast China

Background

First identified in the United States in 2016, porcine circovirus type 3 (PCV3) is a newly emerging porcine circovirus exhibiting a wide range of clinical syndromes, which may be associated with the pathogenicity observed in pigs.

Results

The aim of this study was to identify and characterize the full genome sequence of PCV3 strains circulating in Northeast China. Herein, 105 lung samples isolated from sick pigs in Northeast China during 2018 were analyzed for PCV3. Using PCR, the total PCV3-positive rate was 33.3% (35/105), with rates of 17.8% (8/45), 66.7% (10/15), and 37.8% (17/45) in Heilongjiang, Jilin, and Liaoning province, respectively. Additionally, our findings showed that PCV3-positive samples had a high rate of co-infection with PCV2, PPV6, and PPV7. To study the evolution of the PCV3 in Northeast China, we sequenced the entire genome of 13 strains of PCV3. The results of phylogenetic analyses revealed that PCV3 could be divided into two clades, PCV3a and PCV3b. Interestingly, a G deletion at position 1072 was found in the 1999 nt genome of PCV3-CN2018LN-4 (MH277118). The G deletion terminated replicase protein translation and induced a truncated replicase protein.

Conclusion

These results contribute to the understanding of PCV3 molecular epidemiology and evolution in Northeast China. A new strain of PCV3 with truncated replicase protein was identified.