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•Effect of IBD vaccine (228E®) on S. Enteritidis infected chickens was indicated.•The recorded mortalities were higher in the 228E®+SE infected group.•The anti-S. Enteritidis antibody titres were higher in the SE infected group.•The 228E®+SE group had higher bursal lesion scores than the SE infected group.•Chickens given IBDV vaccine failed antibody response to the S. Enteritidis. Chickens infected with both infectious bursal disease virus (IBDV) and Salmonella had higher mortality. In this work, we investigated the effect of IBDV vaccine (modified live-virus bursal disease vaccine, Nobilis strain 228E®) on experimentally infected chickens with Salmonella Enteritidis (SE). Four experimental groups were included in this study, negative control group, 228E®group, 228E®+SE infected group, and SE infected group. Chickens were ocularly administrated 228E® at 12days of age and orally infected with S. Enteritidis at 13days of age. Sera, intestinal fluid, blood, cloacal swabs and tissue samples were collected at 1, 2 and 3weeks post vaccination (PV). The recorded mortalities were higher in the 228E®+SE infected group, compared to the SE infected group. The anti-S. Enteritidis serum antibody titer and the intestinal mucosal IgA level were higher in the SE infected group at 2 and 3weeks PV, compared to 228E®+SE infected group. S. Enteritidis fecal shedding and organ colonization were significantly higher in the 228E®+SE infected group than the SE infected group at 2 and 3weeks PV. The 228E®+SE group had significantly lower bursa to body weight ratios at 2 and 3weeks PV, as well as had higher bursal lesion scores than the SE infected group. IBDV vaccine depressed the specific-SE systemic and mucosal antibody responses, but did not affect the specific-SE cellular immune responses. Chickens administrated IBDV vaccine, followed by S. Enteritidis infection, could cause a significant effect on the bursa of Fabricius, resulting in failure of systemic and mucosal antibody responses to the S. Enteritidis and reduce the elimination and the clearance of S. Enteritidis.

Both bursin (Lys–His–Gly–NH₂) and Gagnon’s peptides (Lys–Asn–Pro–Tyr) can induce B-cell differentiation. However, it is unclear whether a recombinant hybrid polypeptide consisting of a tandem array of 14 copies of bursin and two copies of Gagnon’s peptide can induce the proliferative activity of lymphocytes. Here, this recombinant hybrid polypeptide was expressed in Escherichia coli and purified by SDS-PAGE. Various assays showed that it not only promoted B-lymphocyte proliferation in vitro but also increased the titers of antibodies directed against infectious bursal disease virus fourfold in the sera of chickens vaccinated with the inactivated infectious bursal disease virus vaccine. The recombinant hybrid polypeptide also reduced the pathological lesions in the bursa of Fabricius caused by infectious bursal disease virus BC6/85. Our results show that this recombinant hybrid polypeptide may be a promising immune adjuvant.

Infectious bursal disease virus (IBDV) is an acute and highly infectious RNA virus known for its immunosuppressive capabilities, chiefly inflicting rapid damage to the bursa of Fabricius (BF) of chickens. Current clinical control of IBDV infection relies on vaccination. However, the emergence of novel variant IBDV (nVarIBDV) has posed a threat to the poultry industry across the globe, underscoring the great demand for innovative and effective vaccines. Our previous studies have highlighted the critical role of IBDV VP5 as an apoptosis-inducer in host cells. In this study, we engineered IBDV mutants via a reverse genetic system to introduce amino acid mutations in VP5. We found that the mutant IBDV-VP5/3m strain caused reduced host cell mortality, and that strategic mutations in VP5 reduced IBDV replication early after infection, thereby delaying cell death. Furthermore, inoculation of chickens with IBDV-VP5/3m effectively reduced damage to BF and induced neutralizing antibody production comparable to that of parental IBDV WT strain. Importantly, vaccination with IBDV-VP5/3m protected chickens against challenges with nVarIBDV, an emerging IBDV variant strain in China, reducing nVarIBDV loads in BF while alleviating bursal atrophy and splenomegaly, suggesting that IBDV-VP5/3m might serve as a novel vaccine candidate that could be further developed as an effective vaccine for clinical control of IBD. This study provides a new clue to the development of novel and effective vaccines.

Infectious bursal disease (IBD), caused by the infectious bursal disease virus (IBDV), significantly threatens global poultry health by inducing immunosuppression and causing economic losses. To enhance vaccination efficacy, we engineered a transgenic strain of Eimeria acervulina (Ea-2C3d) expressing a fusion protein composed of IBDV VP2 and three tandem C3d segments (3C3d), utilizing C3d's adjuvant properties to boost immune responses. The transgene was generated by integrating codon-optimized VP2 and 3C3d sequences into the E. acervulina genome using restriction enzyme-mediated transfection. PCR, protein, and genome sequencing confirmed the successful integration and expression of VP2 fusion C3d, but only two copies of C3d were successfully expressed, due to a partial deletion of one C3d copy during the transfection process. In vivo studies demonstrated that Ea-2C3d elicited significantly higher anti-VP2 antibody titers than the parental Ea-VP2 strain (P < 0.05), especially following second immunization. Upon challenge with virulent IBDV, chickens immunized with Ea-2C3d displayed reduced bursal lesions (histopathological score ≤ 1) and maintained bursal integrity (bursal index >0.7), comparable to those receiving a commercial subunit vaccine. Despite reduced reproductive capacity in the transgenic parasites, Ea-2C3d maintained its immunogenicity and safety. These findings highlight that C3d adjuvant enhances VP2-mediated protection in a coccidial vector, presenting a novel dual-protection strategy against IBD and coccidiosis.

Infectious bursal disease virus (IBDV) induces severe immunosuppression in chickens, leading to significant economic losses in the global poultry industry. This study investigated 52 chicken flocks, including commercial broilers, layers, and baladi, from various Egyptian governorates in 2023. These flocks exhibited symptoms of depression, along with kidney and bursa lesions, indicative of IBDV infection. Pooled Bursal homogenates were tested using RT-PCR with VP2-specific primers, revealing that 20 flocks tested positive for IBDV. Six representative samples were selected from 20 positive flocks for isolation in embryonated chicken eggs. The embryonic lesions observed included haemorrhage, skull swelling, and liver necrosis with a pale-yellow appearance, in addition to congestion and thickening in the chorioallantoic membrane (CAM). Partial amplification of the VP2 gene from the harvested embryo suspensions of the six IBDV isolates was performed for sequencing. Phylogenetic analysis of the sequences revealed that five IBDV isolates (VV4, VV5, VV6, VV10, and VV16) belonged to the very virulent strain group A3 cluster, whereas one isolate (VV2) clustered with Chinese Variant strains in the A2d group. Sequence analysis of the hypervariable region (HVR) of VP2 compared to that of Egypt-USC-IBD-1-2019 and vvIBDV/Beh21/Egypt/18 highly virulent IBDV strains revealed several amino acid mutations. The VP2 HVR of all isolates maintained the serine-rich heptapeptide sequence SWSASGS, which is adjacent to the major hydrophilic peak B and serves as a virulence marker. Histopathological examination revealed that bursae from chickens infected with vvIBDV exhibited marked interlobular oedema and lymphoid depletion. In contrast, bursae from chickens infected with Variant IBDV showed massive lymphoid depletion, with hyperplasia of the bursal capsule. These findings highlight the circulation of both virulent and Variant IBDV strains in Egyptian chicken flocks, complicating disease control. Consequently, there is a need to update vaccination programs and vaccine strains for IBDV in Egypt.

The control of poultry diseases has relied heavily on the use of many live and inactivated vaccines. However, over the last 30 yr, recombinant DNA technology has been used to generate many novel poultry vaccines. Fowlpox virus and turkey herpesvirus are the two main vectors currently used to construct recombinant vaccines for poultry. With the use of these two vectors, more than 15 recombinant viral vector vaccines against Newcastle disease, infectious laryngotracheitis, infectious bursal disease, avian influenza, and Mycoplasma gallisepticum have been developed and are commercially available. This review focuses on current knowledge about the safety and efficacy of recombinant viral vectored vaccines and the mechanisms by which they facilitate the control of multiple diseases. Additionally, the development of new recombinant vaccines with novel vectors will be briefly discussed.

We report the complete nucleotide sequence of a reassortant infectious bursal disease (IBD) virus (IBDV) HN isolate from commercial broiler flocks in central China. The genome consisted of 3,232 and 2,652 nucleotides in the coding regions of segments A and B, respectively. Alignment of both nucleotide and deduced amino acid sequences and phylogenetic analysis revealed that the genome segments A and B of HN were derived from the attenuated strain B87 and the VV strain OKYM. This is a new reassortant IBDV strain that has emerged in nature, involving segment A of a cell-culture-adapted attenuated vaccine strain B87.

•Modified live (MdLV) rather than HVT-IBDV vaccine delays neonatal varIBDV infection.•varIBDV replicates early in HVT-IBDV compared to MdLV vaccinated chicks.•HVT-IBDV vaccine induces suppression of T-cell response.•First week after HVT-IBDV vaccination demands strict biosecurity. Chickens are commonly processed around 35–45days of age in broiler chicken industry hence; diseases that occur at a young age are of paramount economic importance. Early age infection with infectious bursal disease virus (IBDV) results in long-lasting immunosuppression and profound economic losses. To our knowledge, this is the first study comparing the protection efficacy of modified live (MdLV) IBDV and herpesvirus turkey (HVT)-IBDV vaccines against early age variant IBDV (varIBDV) infection in chicks. Experiments were carried out in IBDV maternal antibody (MtAb) positive chicks (n=330), divided into 6 groups (n=50–60/group), namely Group 1 (saline), Group 2 (saline+varIBDV), Group 3 (HVT-IBDV), Group 4 (HVT-IBDV+varIBDV), Group 5 (MdLV) and Group 6 (MdLV+varIBDV). HVT-IBDV vaccination was given via the in ovo route to 18-day-old embryonated eggs. MdLV was administered via the subcutaneous route in day-old broilers. Group 2, Group 4 and Group 6 were orally challenged with varIBDV (SK-09, 3×103 EID50) at day 6 post-hatch. IBDV seroconversion, bursal weight to body weight ratio (BBW) and bursal histopathology were assessed at 19 and 35days of age. Histopathological examination at day 19 revealed that varIBDV-SK09 challenge caused severe bursal atrophy and lower BBW in HVT-IBDV but not in MdLV vaccinated chicks. However by day 35, all challenged groups showed bursal atrophy and seroconversion. Interestingly, RT-qPCR analysis after varIBDV-SK09 challenge demonstrated an early (9days of age) and significantly high viral load (∼5744 folds) in HVT-IBDV vaccinated group vs unvaccinated challenged group (∼2.25 folds). Furthermore, flow cytometry analysis revealed inhibition of cytotoxic CD8+ T-cell response (CD44-downregulation) and decreased splenic lymphocytes counts in chicks after HVT-IBDV vaccination. Overall, our data suggest that MdLV delays varIBDV pathogenesis, whereas, HVT-IBDV vaccine is potentially immunosuppressive, which may increase the risk of early age varIBDV infection in broilers.

Infectious bursal disease virus (IBDV) is one of the most important immunosuppressive viral agents in poultry production. Prophylactic vaccinations of chicken flocks are the primary tool for disease control. Widely used immunoprophylaxis can, however, provide high pressure which contributes to the genetic diversification of circulating viruses, e.g. through reassortment of genome segments. We report the genetic and phenotypic characterization of a field reassortant IBDV (designated as Bpop/03) that acquired segment A from very virulent IBDV and segment B from classical attenuated D78-like IBDV. Despite the mosaic genetic make-up, the virus caused high mortality (80%) in experimentally infected SPF chickens and induced lesions typical of the acute form of IBD. The in vivo study results are in contrast with the foregoing experimental investigations in which the natural reassortants exhibited an intermediate pathotype, and underline the complex nature of IBDV virulence.

Infectious bursal disease (IBD) is a viral immunosuppressive disease of chickens attacking mainly an important lymphoid organ in birds [the bursa of Fabricius (BF)]. The emergence of new variant strains of the causative agent [infectious bursal disease virus (IBDV)] has made it more urgent to develop new vaccination strategies against IBD. One of these strategies is the use of recombinant vaccines (DNA and viral-vectored vaccines). Several studies have investigated the host immune response towards IBDV. This review will present a detailed background on the disease and its causative agent, accompanied by a summary of the most recent findings regarding the host immune response to IBDV infection and the use of recombinant vaccines against IBD.