Genotyping and Molecular Characterization of Infectious Bursal Disease Virus Identified in Important Poultry-Raising Areas of China During 2019 and 2020

Genetic characterization of infectious bursal disease virus strains with distinct VP2 amino acid profiles emerging in Pakistan

Infectious bursal disease (IBDV) poses a significant threat to the global poultry industry and causes major economic losses. This study presents the genetic profile of IBDV strains emerging in Pakistan, focusing on the VP2 amino acid profile. The effects of these changes on disease transmission, vaccine effectiveness, and overall chicken health are concerning. A meticulous analysis was carried out by isolating and clustering IBDV strains collected from Faisalabad district of Pakistan. The genetics of these viruses were evaluated by analyzing the VP2 gene, the main component of the virus. Importantly, our results reveal the existence of IBDV strains with unprecedented VP2 amino acid profiles, indicating genetic changes that may affect virulence and immunity. This study highlighted the changing IBDV landscape in Pakistan and underscores the importance of continued research and surveillance efforts. Understanding the genetic structure of these emerging diseases is essential for developing effective control strategies, including vaccine development and control. This also emphasized the need for international cooperation to reduce the spread of the new IBDV strains, which could significantly impact the poultry industry outside Pakistan.

Novel Antigenic Variant Infectious Bursal Disease Virus Outbreaks in Japan from 2014 to 2023 and Characterization of an Isolate from Chicken

Novel antigenic variant strains of the infectious bursal disease virus (IBDV) classified into genogroup A2d have been found in the western part of Japan since 2017. Novel antigenic variant IBDVs now occur in higher frequencies in poultry houses and have been detected in the eastern part of Japan, indicating the spread of IBDVs despite the usual IBDV vaccination. We isolated a novel antigenic variant IBDV, designated as the B2977CE2C3 strain. The B2977CE2C3 strain had two genogroup A2d specific amino acids-lysine and isoleucine, at 221 and 252 aa-along with the other genogroup A2 common amino acids in the projection domains of the VP2 protein corresponding to the virus-neutralizing epitopes and viral pathogenicity. Experimental infection of the B2977CE2C3 strain did not produce any apparent clinical signs in the specific-pathogen-free chickens during the observation period (21 days), but atrophy of the bursa of Fabricius (BF) was apparent. The mean BF to the body weight ratio was 0.35 in negative control chickens at 21 days post-infection (pi) but 0.06 in the B2977CE2C3 infected group. An extremely high copy number of the IBDV genome (>108 copies/µL) was observed in the BF at 3 days pi, while a high copy number of the IBDV genome (>106 copies/µL) was observed in the thymus, spleen cecal tonsil, and bone marrow even though macroscopic lesions were not apparent in these organs.

Pathology and VP2-Based Characterization of Infectious Bursal Disease Virus Associated with an Outbreak in Layer Chickens in Ghana

Infectious bursal disease (IBD) continues to threaten poultry production globally, with highly virulent strains circulating in many parts of Africa. In this study, molecular characterization was performed on a circulating infectious bursal disease virus (IBDV) strain from an outbreak in a layer flock in Ghana. Layer chicks presented for necropsy had markedly enlarged and hemorrhagic bursae of Fabricius, with necrotic foci and catarrhal exudate on the serosal surface. Histopathology of the bursa of Fabricius revealed scattered to effacing hemorrhages on the plicae, extensive necrosis with expansion of the stroma between the follicles, and depletion of lymphocytes within the interfollicular epithelium. Reverse transcription polymerase chain reaction (RT-PCR) and subsequent sequencing of the VP2 gene showed the presence of IBDV in formalin-fixed paraffin-embedded tissues. A phylogenetic analysis compared 62 other IBDV sequences from different parts of the world and placed the Ghanaian IBDV in genogroup 3 (vvIBDV), closely related to IBDV from Nigeria. In comparison to reference vvIBDV, there were amino acid substitutions at positions 252, 254, and 300. To the best of our knowledge, this is the first report in which an IBDV from a disease outbreak in Ghana has been sequenced and compared with other IBDVs in a phylogenetic analysis.

Standardization and validation of a novel reverse transcriptase polymerase chain reaction method for detecting virulent strains of the infectious bursal disease virus

Background and Aim

Gumboro disease is an economically crucial veterinary condition in chickens. It is caused by the infectious bursal disease virus (IBDV). This virus consists of two serotype groups, of which serotype I strain is pathogenic to chickens. For many years, the development of molecular techniques for either diagnostic purposes or surveillance of the appearance of new pathogenic strains has mainly focused on targeting the VP2 genomic region. However, due to the constant necessity for the discrimination between already prevalent vaccine strains and new pathogenic strains of this virus, it becomes imperative to have an immediate molecular method targeting a consensus sequence to achieve this task using field samples to reduce costs. Consequently, we focused on developing a novel reverse transcriptase polymerase chain reaction (RT-PCR) procedure solely for this purpose.

Materials and Methods

Eight VP5 sequences were aligned, and the sequence with the majority of nucleotide coincidences was used to design a set of consensus primers. Then, a pathogenic strain of IBDV was propagated in embryonated chicken eggs, and the viral RNA was extracted. Finally, the conditions for this novel RT-PCR were evaluated using a commercial kit and the newly designed primers.

Results

After determining the optimal RT-PCR conditions, the newly designed primers successfully amplified a 402-bp consensus sequence of the VP5 gene. In addition, these primers specifically amplified the VP5 sequence of the IBDV-positive samples, not the other samples previously confirmed to be positive for other common poultry pathogens.

Conclusion

Our novel RT-PCR procedure has been demonstrated to be helpful in selectively amplifying the consensus sequence of the VP5 gene, indicating that this novel RT-PCR procedure constitutes an important and useful tool to execute initial discrimination of field-retrieved samples containing and not containing virulent strains of this virus before deciding to execute a blindly and more costly sequencing procedure of all the samples together.

Rapid identification, pathotyping and quantification of infectious bursal disease virus by high-resolution melting curve quantitative reverse transcription PCR analysis: An innovative technology well-suited for real-time large-scale epidemiological surveillance

With the virus continuing to evolve, very virulent IBDV (vvIBDV) and novel variant IBDV (nvIBDV) have become the predominant epidemic strains in China, exacerbated by the widespread use of attenuated vaccine strains (attIBDV), making a complex infection situation of IBDV in the field. Therefore, developing a rapid and accurate high-resolution melting curve quantitative reverse transcription PCR (HRM-qRT-PCR) for the identification and pathotyping of IBDV is crucial for clinical monitoring and disease control. Extensive data analysis and genome-screening of the three dominant IBDV pathotypes identified a specific region (nucleotides 2450-2603 in segment A) with distinct GC content as the detection target. Experimental testing of HRM-qRT-PCR revealed distinct melting curves and high sensitivity, with the detection limits of 61.2 copies/μL, 61.1 copies/μL and 67.5 copies/μL for vvIBDV, nvIBDV and attIBDV, respectively. The method exhibited excellent specificity, with no inter-genotypes cross-reactivity among the three pathotypes and no reactivity to other common avian pathogens. Applied to samples with double and triple co-infections of different IBDV pathotypes, the method displayed specific melting peaks corresponding to the viruses present in the samples, with an accuracy rate of 100 %. This method precisely identifies and differentiates all the single or co-infected samples, generating distinct peaks corresponding to the Tm values of each virus pathotype in traditional melting curve plots. Furthermore, the method overcomes the limitations of traditional pathotyping methods, requiring only one reaction to achieve rapid viral pathotyping and facilitating quantitative analysis of viruses within the samples. This study introduces an innovative HRM-qRT-PCR method, offering new technology to rapid and accurate identification, pathotyping and quantification of vvIBDV, nvIBDV, and attIBDV. With strong discriminatory power, user-friendliness and a short processing time, this method is highly attractive for the rapid IBDV pathotyping in real-time large-scale epidemiological surveillance during outbreaks.

The complete protections induced by the oil emulsion vaccines of the novel variant infectious bursal disease viruses against the homologous challenges indicating the important roles of both VP2 and VP1 in the antigenicity and pathogenicity of the virus

Novel variant infectious bursal disease virus (nvIBDV) is an emerging genotype (A2dB1b) that can cause severe and prolonged immunosuppression in young chickens. Despite current commercial vaccines being proven to lack complete protection against nvIBDV, it remains unclear whether the oil emulsion inactivated vaccines (OEVs) of the homologous and heterologous virus or booster immunization can provide effective protection. In this study, OEVs with two types of nvIBDV isolates QZ191002 (A-nv/B-nv) and YL160304 (A-nv/B-HLJ0504-like) were prepared and evaluated the protective effects of OEVs plus the booster immunizations with different current commercial vaccines against the challenge of nvIBDVs. The results from vaccination-challenge experiments showed that nvIBDV could break through the protection provided by only one immunization dose of the commercial vaccines, with the protection rates ranging from 40% to 60%. Interestingly, even with booster immunization with different commercial vaccines, the protection rates could only be increased to 60%-80%. As expected, only the OEVs of the homologous virus could provide 100% protection against the homologous nvIBDV, which could induce high-level specific antibodies, ameliorate target organ damage, and significantly reduce the viral load of the bursal in the challenged chickens. Notably, YL160304-OEV performed better than QZ191002-OEV, providing 100% protection not only against the challenge of homologous strain but also against that of heterologous QZ191002 strain. Antibody levels of the immunized chickens gradually increased after a short decline and reached the highest level on the age of 28 days. Similarly, the percentages of lymphocytes CD4+, CD8+ T, and B in peripheral blood lymphocytes (PBLs) were significantly increased on 21 d and 28 d. Notably, despite the nvIBDV, OEVs initially induced a delayed responses in the early stages but ultimately reach higher levels of CD4+ and CD8+ T lymphocytes. The results of study suggest that even booster immunization with different commercial vaccines cannot provide complete protection against nvIBDV, while the OEVs made by the nvIBDVs can provide full protection. Moreover, YL160304-OEV exhibits a broader protective spectrum against different nvIBDV strains, making it a potential candidate for the development of new vaccine.

Loop PDE of viral capsid protein is involved in immune escape of the emerging novel variant infectious bursal disease virus

Infectious bursa disease (IBD) is an acute, highly contactable, lethal, immunosuppressive infectious disease caused by the Infectious bursa disease virus (IBDV). Currently, the emerged novel variant IBDV (nVarIBDV) and the sustainedly prevalent very virulent IBDV (vvIBDV) are the two most prevalent strains of IBDV in China. The antigenic properties of the two prevalent strains differed significantly, which led to the escape of nVarIBDV from the immune protection provided by the existing vvIBDV vaccine. However, the molecular basis of the nVarIBDV immune escape remains unclear. In this study, we demonstrated, for the first time, that residues 252, 254, and 256 in the PDE of VP2 are involved in the immune escape of the emerging nVarIBDV. Firstly, the IFA-mediated antigen-antibody affinity assay showed that PBC and PDE of VP2 could affect the affinity of vvIBDV antiserum to VP2, of which PDE was more significant. The key amino acids of PDE influencing the antigen-antibody affinity were also identified, with G254N being the most significant, followed by V252I and I256V. Then the mutated virus with point or combined mutations was rescued by reverse genetics. it was further demonstrated that mutations of V252I, G254N, and I256V in PDE could individually or collaboratively reduce antigen-antibody affinity and interfere with antiserum neutralization, with G254N being the most significant. This study revealed the reasons for the widespread prevalence of nVarIBDV in immunized chicken flocks and provided innovative ideas for designing novel vaccines that match the antigen of the epidemic strain.

ADP-ribosylation factor 6 promotes infectious bursal disease virus replication by affecting the internalization process via clathrin

ADP-ribosylation factor 6 (ARF6) is a small G protein with extensive functions, including regulation of cellular membrane transport and viral infection. Infectious bursal disease (IBD) is caused by infectious bursal disease virus (IBDV), which mainly invades the bursa of Fabricius and causes low immunity in poultry. Our study demonstrated that IBDV infection could promote the expression of ARF6; however, the underlying mechanism remains unclear. Herein, the function of ARF6 in IBDV infection was explored, and it was revealed that viral replication was significantly promoted by ARF6 overexpression and hampered by siRNA-mediated inhibition of ARF6. Using two site mutants of ARF6 (ARF6-T27N and ARF6-Q67L), we found that IBDV replication was repressed by ARF6-T27N, indicating that ARF6 promotes IBDV replication. Further exploration of its mechanism revealed that ARF6 affects the copy number of IBDVs entering cells. A clathrin inhibitor (pitstop 2) impeded the early replication of IBDV, even when ARF6 was overexpressed. These results indicated that ARF6 promotes viral replication by affecting the internalization of IBDV, which may involve clathrin-dependent endocytosis. Our findings improve the understanding of the processes governing IBDV infection and provide insights into its prevention and control.

Isolation and genomic characteristics of the novel variant infectious bursal disease virus in China

The infectious bursal disease virus (IBDV) is a member of the viruses that can induce immunosuppression in chickens. In recent years, more and more IBDV-infected cases by the novel variant IBDV were reported in China, and it has been demonstrated that currently used vaccines could not provide complete protection against these new IBDV variants. However, a lack of comprehensive analysis of the genomic characteristics of the novel variant strain IBDV has hampered its vaccine development. In this study, a strain of IBDV, designated HB202201, was phylogenetically analyzed, and it was found that the hypervariable region (HVR) of VP2 belonged to the novel variant strain. Furthermore, the 5'- and 3'-ends of segments A and B were analyzed using the rapid amplification of cDNA end (RACE) method. After the full-length of segment A and segment B were determined, the phylogenetic analysis of the segment A and segment B showed that the isolated HB202201 belonged to A2dB1 genotype, which demonstrated the HB202201 belonged to the novel variant strain. In addition, the specific mutations in VP1-VP5 amino acids were analyzed, which showed that there were multiple typical mutations in novel variant IBDV proteins, including VP1 (G24, I141, V163, and E240), VP2 (K221, and I252), VP3 (Q167 and L196), and VP5 (R7, P44, R92, G104, and E147), whereas there was no typical mutation in VP4. This study provides insights into the genomic and antigenic characteristics of the novel variant IBDV, which will promote the development of novel vaccine against the novel variant IBDV.

The attenuated live vaccine strain W2512 provides protection against novel variant infectious bursal disease virus

Infectious bursal disease virus (IBDV) causes an acute and highly contagious infectious disease characterized by severe immunosuppression, causing great economic losses to the poultry industry globally. Over the past 30 years, this disease has been well controlled through vaccination and strict biosafety measures. However, novel variant IBDV strains have emerged in recent years, posing a new threat to the poultry industry. Our previous epidemiological survey showed that few novel variant IBDV strains had been isolated from chickens immunized with the attenuated live vaccine W2512-, suggesting that this vaccine is efficacious against novel variant strains. Here, we report the protective effect of the W2512 vaccine against novel variant strains in SPF chickens and commercial yellow-feathered broilers. We found that W2512 causes severe atrophy of the bursa of Fabricius in SPF chickens and commercial yellow-feathered broilers, induces high levels of antibodies against IBDV, and protects chickens from infection with the novel variant strains via a placeholder effect. This study highlights the protective effect of commercial attenuated live vaccines against the novel IBDV variant and provides guidance for the prevention and control of this disease.

Phylogenotyping of infectious bursal disease virus in Vietnam according to the newly unified genotypic classification scheme

Since 1987, infectious bursal disease virus (IBDV) has circulated and evolved in Vietnam, but little is known about the genotypes present. IBDV samples were collected in 1987, 2001-2006, 2008, 2011, 2015-2019, and 2021 in 18 provinces. We conducted phylogenotyping analysis based on an alignment of 143 VP2-HVR (hypervariable region) sequences from 64 Vietnamese isolates (26 previous and 38 additional sequences and two vaccines, and alignment of 82 VP1 B-marker sequences, including one vaccine and four Vietnamese field strains. The analysis identified three A-genotypes, A1, A3, and A7, and two B-genotypes, B1 and B3, among the Vietnamese IBDV isolates. The lowest average evolutionary distance (8.6%) was seen between the A1 and A3 genotypes, and the highest (21.7%) was between A5 and A7, while there was a distance of 14% between B1 and B3 and 17% between B3 and B2. Unique signature residues were observed for genotypes A2, A3, A5, A6, and A8, which could be used for genotypic discrimination. A timeline statistical summary revealed that the A3-genotype predominated (79.8% presence) in Vietnam from 1987 to 2021 and that it remained the dominant IBDV genotype over the last five years (2016-2021). The current study contributes to a better understanding of the circulating genotypes and evolution of IBDV in Vietnam and worldwide.

Comparative Pathogenicity of Three Strains of Infectious Bursal Disease Virus Closely Related to Poultry Industry

Infectious bursal disease (IBD) is an acute, highly contagious, immunosuppressive, and fatal infectious disease of young chickens caused by infectious bursal disease virus (IBDV). Since 2017, a new trend has been discovered in the IBDV epidemic, with very virulent IBDV (vvIBDV) and novel variant IBDV (nVarIBDV) becoming the two current dominant strains in East Asia including China. In this study, we compared the biological characteristics of the vvIBDV (HLJ0504 strain), nVarIBDV (SHG19 strain), and attenuated IBDV (attIBDV, Gt strain) using specific-pathogen-free (SPF) chicken infection model. The results showed that vvIBDV distributed in multiple tissues, replicated the fastest in lymphoid organs such as bursa of Fabricius, induced significant viremia and virus excretion, and is the most pathogenic virus with a mortality of more than 80%. The nVarIBDV had a weaker replication capability and did not kill the chickens but caused severe damage to the central immune organ bursa of Fabricius and B lymphocytes and induced significant viremia and virus excretion. The attIBDV strain was found not to be pathogenic. Further studies preliminarily suggested that the expression level of inflammatory factors triggered by HLJ0504 was the highest, followed by the SHG19 group. This study is the first to systematically compare the pathogenic characteristics of three IBDVs closely related to poultry industry from the perspectives of clinical signs, micro-pathology, virus replication, and distribution. It is of great importance to obtain an extensive knowledge of epidemiology, pathogenicity, and comprehensive prevention, and control of various IBDV strains.

Genetic Insight into the Interaction of IBDV with Host-A Clue to the Development of Novel IBDV Vaccines

Infectious bursal disease virus (IBDV) is an immunosuppressive pathogen causing enormous economic losses to the poultry industry across the globe. As a double-stranded RNA virus, IBDV undergoes genetic mutation or recombination in replication during circulation among flocks, leading to the generation and spread of variant or recombinant strains. In particular, the recent emergence of variant IBDV causes severe immunosuppression in chickens, affecting the efficacy of other vaccines. It seems that the genetic mutation of IBDV during the battle against host response is an effective strategy to help itself to survive. Therefore, a comprehensive understanding of the viral genome diversity will definitely help to develop effective measures for prevention and control of infectious bursal disease (IBD). In recent years, considerable progress has been made in understanding the relation of genetic mutation and genomic recombination of IBDV to its pathogenesis using the reverse genetic technique. Therefore, this review focuses on our current genetic insight into the IBDV's genetic typing and viral genomic variation.

The Over-40-Years-Epidemic of Infectious Bursal Disease Virus in China

Infectious bursal disease (IBD) is an acute, highly contagious, immunosuppressive disease of chickens caused by the virus (IBDV), which critically threatens the development of the global chicken industry and causes huge economic losses. As a large country in the poultry industry, the epidemic history of IBDV in China for more than 40 years has been briefly discussed and summarized for the first time in this report. The first classic strain of IBDV appeared in China in the late 1970s. In the late 1980s and early 1990s, the very virulent IBDV (vvIBDV) rapidly swept across the entirety of China, threatening the healthy development of the poultry industry for more than 30 years. Variants of IBDV, after long-term latent circulation with the accumulation of mutations since the early 1990s, suddenly reappeared as novel variant strains (nVarIBDV) in China in the mid-2010s. Currently, there is a coexistence of various IBDV genotypes; the newly emerging nVarIBDV of A2dB1 and persistently circulating vvIBDV of A3B3 are the two predominant epidemic strains endangering the poultry industry. Continuous epidemiological testing and the development of new prevention and control agents are important and require more attention. This report is of great significance to scientific cognition and the comprehensive prevention and control of the IBDV epidemic.

Genetics and Pathogenicity of Natural Reassortant of Infectious Bursal Disease Virus Emerging in Latvia

Infectious bursal disease virus is an immunosuppressive pathogen that, despite applied vaccination, is affecting the poultry industry worldwide. This report presents the genetic and pathotypic characterization of a natural reassortant emerging in Europe (Latvia). Genetic characterization showed that strain 25/11/Latvia/2011 represents genotype A3B1, whose segment A is derived from very virulent strains, while segment B is from the classic-like genogroup. Phylogenetic maximum likelihood inference of the B-segment sequence clustered the reassortant strain together with the US antigenic variant E strain. However, the obtained full-length sequence of 25/11/Latvia/2011 revealed that not only reassortment but also dozens of mutations shaped the unique genetic makeup. Phenotypic characterization showed no mortality and no clinical signs of disease but a severe bursa of Fabricius atrophy and splenomegaly in the convalescent birds at 10 days post infection. The results obtained indicate that the acquired genetic constellation contributed to a decrease in virulence; nevertheless, the infection causes severe damage to lymphoid organs, which can lead to impaired immune responses.

Residues 318 and 323 in capsid protein are involved in immune circumvention of the atypical epizootic infection of infectious bursal disease virus

Recently, atypical infectious bursal disease (IBD) caused by a novel variant infectious bursal disease virus (varIBDV) suddenly appeared in immunized chicken flocks in East Asia and led to serious economic losses. The epizootic varIBDV can partly circumvent the immune protection of the existing vaccines against the persistently circulating very virulent IBDV (vvIBDV), but its mechanism is still unknown. This study proved that the neutralizing titer of vvIBDV antiserum to the epizootic varIBDV reduced by 7.0 log2, and the neutralizing titer of the epizootic varIBDV antiserum to vvIBDV reduced by 3.2 log2. In addition, one monoclonal antibody (MAb) 2-5C-6F had good neutralizing activity against vvIBDV but could not well recognize the epizootic varIBDV. The epitope of the MAb 2-5C-6F was identified, and two mutations of G318D and D323Q of capsid protein VP2 occurred in the epizootic varIBDV compared to vvIBDV. Subsequently, the indirect immunofluorescence assay based on serial mutants of VP2 protein verified that residue mutations 318 and 323 influenced the recognition of the epizootic varIBDV and vvIBDV by the MAb 2-5C-6F, which was further confirmed by the serial rescued mutated virus. The following cross-neutralizing assay directed by MAb showed residue mutations 318 and 323 also affected the neutralization of the virus. Further data also showed that the mutations of residues 318 and 323 of VP2 significantly affected the neutralization of the IBDV by antiserum, which might be deeply involved in the immune circumvention of the epizootic varIBDV in the vaccinated flock. This study is significant for the comprehensive prevention and control of the emerging varIBDV.

Dynamics of the Emerging Genogroup of Infectious Bursal Disease Virus Infection in Broiler Farms in South Korea: A Nationwide Study

Infectious bursal disease (IBD), caused by IBD virus (IBDV), threatens the health of the poultry industry. Recently, a subtype of genogroup (G) 2 IBDV named G2d has brought a new threat to the poultry industry. To determine the current status of IBDV prevalence in South Korea, active IBDV surveillance on 167 randomly selected broiler farms in South Korea from August 2020 to July 2021 was conducted. The bursas of Fabricius from five chickens from each farm were independently pooled and screened for IBDV using virus-specific RT-PCR. As a result, 86 farms were found to be infected with the G2d variant, 13 farms with G2b, and 2 farms with G3. Current prevalence estimation of IBDV infection in South Korea was determined as 17.8% at the animal level using pooled sampling methods. G2d IBDV was predominant compared to other genogroups, with a potentially high-risk G2d infection area in southwestern South Korea. The impact of IBDV infection on poultry productivity or Escherichia coli infection susceptibility was also confirmed. A comparative pathogenicity test indicated that G2d IBDV caused severe and persistent damage to infected chickens compared with G2b. This study highlights the importance of implementation of regular surveillance programs and poses challenges for the comprehensive prevention of IBDV infections.

Infectious bursal disease virus' interferences with host immune cells: What do we know?

AbstractInfectious bursal disease virus (IBDV) induces one of the most important immunosuppressive diseases in chickens leading to high economic losses due increased mortality and condemnation rates, secondary infections and the need for antibiotic treatment. Over 400 publications have been listed in PubMed.gov in the last five years pointing out the research interest in this disease and the development of improved preventive measures. While B cells are the main target cells of the virus, also other immune and non-immune cell populations are affected leading a multifaceted impact on the normally well orchestrated immune system in IBDV-infected birds. Recent studies clearly revealed the contribution of innate immune cells as well as T cells to a cytokine storm and subsequent death of affected birds in the acute phase of the disease. Transcriptomics identified differential regulation of immune related genes between different chicken genotypes as well as virus strains, which may be associated with a variable disease outcome. The recent availability of primary B cell culture systems allowed a closer look into virus-host interactions during IBDV-infection. The new emerging field of research with transgenic chickens will open up new opportunities to understand the impact of IBDV on the host also under in vivo conditions, which will help to understand the complex virus-host interactions further.