Genetic Sequence and Pathogenicity of Infectious Bursal Disease Virus in Chickens in Egypt During 2017-2021.

The continued circulation of infectious bursal disease virus (IBDV) in Egypt, despite the use of various vaccines, is a serious problem that requires continuous detection of IBDV. In the current study, real-time reverse transcriptase polymerase chain reaction testing of 100 diseased chicken flocks during 2017-2021 revealed the presence of very virulent IBDV (vvIBDV) in 67% of the flocks, non-vvIBDV in 11%, and a mixture of both vvIBDV and non-vvIBDV in 4%. Twenty-nine IBDV isolates were submitted for partial sequencing of the viral protein 2 hypervariable region (VP2-HVR), and 27 isolates were confirmed to be genogroup A3 (vvIBDV) with 96.3%-98.5% similarity to the global A3 (vvIBDV) and 88.9%-97% similarity to genogroup A1 vaccine strains. The remaining two isolates were non-vvIBDV and showed 91.1% and 100% identity with classical genogroup A1 strains, respectively. Furthermore, the sequence and phylogenetic analysis of VP1 (amino acids 33-254) of two selected isolates of A3, 5/2017 and 98/2021, clustered them as B2, vvIBDV-like, strains with high similarity (99.5%) to four Egyptian, 99% to Chinese and European, and 97.7% to Chinese and Polish vvIBDV isolates. Experimental infection of commercial broiler chickens with two vvIBDV-A3B2 isolates (5/2017 and 98/2021) showed no mortality despite typical tissue lesions, clear histopathological changes, and strong ELISA antibody response. Isolate 98/2021 was more pathogenic, as confirmed by histopathology, whereas isolate 5/2017 induced a stronger serological response. In conclusion, vvIBDV (A3B2) strains with two amino acid (aa) substitutions in VP1 as V141I and V234I as well as VP2 as Y220F and G254S are still circulating in Egypt.

Análisis de las secuencias genéticas y de la patogenicidad del virus de la enfermedad infecciosa de la bolsa de pollos en Egipto durante los años 2017­2021. La circulación continua del virus de la enfermedad infecciosa de la bolsa (IBDV) en Egipto, a pesar del uso de varias vacunas, continua siendo un problema serio que requiere la detección continua de este virus. En el presente estudio, se realizó una prueba de transcripción reversa y reacción en cadena de la polimerasa en tiempo real de 100 parvadas enfermas de pollos durante los años 2017­2021 y reveló la presencia de virus muy virulentos (vvIBDV) en el 67% de las parvadas, otros tipos diferentes a los muy virulentos en el 11%, y una mezcla de virus muy virulentos y otros tiposen un 4% de las parvadas. Se enviaron veintinueve aislados del virus de la enfermedad infecciosa de la bolsa para la secuenciación parcial de la región hipervariable de la proteína viral 2 (VP2-HVR), y se confirmó que 27 aislados pertenecían al genogrupo A3 (vvIBDV) con una similitud del 96.3% al 98.5% con el genogrupo A3 global (vvIBDV) y de 88.9% a 97% de similitud con las cepas vacunales del genogrupo A1. Los dos aislamientos restantes no resultaron ser muy virulentos y mostraron un 91.1% y un 100% de identidad con las cepas clásicas del genogrupo A1, respectivamente. Además, la secuencia y el análisis filogenético de la proteina VP1 (aminoácidos 33-254) de dos aislados seleccionados de genogrupo A3, 5/2017 y 98/2021, los agruparon como cepas B2, similares a virus muy virulentos, con alta similitud (99.5%) con cuatro aislamientos de Egipto, con similitud de 99% con aislados chinos y europeos, y de 97.7% con aislados muy virulentos chinos y polacos. La infección experimental de pollos de engorde comerciales con dos aislados muy virulentos tipo A3B2 (5/2017 y 98/2021) no mostró mortalidad a pesar de las lesiones tisulares típicas, los cambios histopatológicos claros y la fuerte respuesta de anticuerpos por ELISA. El aislado 98/2021 fue más patógeno, según lo confirmado por histopatología, mientras que el aislado 5/2017 indujo una respuesta serológica más fuerte. En conclusión, las cepas muy virulentas (A3B2) con dos sustituciones de aminoácidos (aa) en la proteina VP1 como V141I y V234I, así como en VP2 tales como Y220F y G254S, todavía circulan en Egipto.

Simultaneous construction strategy using two types of fluorescent markers for HVT vector vaccine against infectious bursal disease and H9N2 avian influenza virus by NHEJ-CRISPR/Cas9.

Recently, herpesvirus of turkeys (HVT), which was initially employed as a vaccine against Marek's disease (MD), has been shown to be a highly effective viral vector for producing recombinant vaccines that can simultaneously express the protective antigens of multiple poultry diseases. Prior to the development of commercial HVT-vectored dual-insert vaccines, the majority of HVT-vectored vaccines in use only contained a single foreign gene and were often generated using time-consuming and inefficient traditional recombination methods. The development of multivalent HVT-vectored vaccines that induce simultaneous protection against several avian diseases is of great value. In particular, efficacy interference between individual recombinant HVT vaccines can be avoided. Herein, we demonstrated the use of CRISPR/Cas9 gene editing technology for the insertion of an IBDV (G2d) VP2 expression cassette into the UL45/46 region of the recombinant rHVT-HA viral genome to generate the dual insert rHVT-VP2-HA recombinant vaccine. The efficacy of this recombinant virus was also evaluated in specific pathogen-free (SPF) chickens. PCR and sequencing results showed that the recombinant virus rHVT-VP2-HA was successfully constructed. Vaccination with rHVT-VP2-HA produced high levels of specific antibodies against IBDV (G2d) and H9N2/Y280. rHVT-VP2-HA can provide 100% protection against challenges with IBDV (G2d) and H9N2/Y280. These results demonstrate that rHVT-VP2-HA is a safe and highly efficacious vaccine for the simultaneous control of IBDV (G2d) and H9N2/Y280.

Emergence of the novel infectious bursal disease virus variant in vaccinated poultry flocks in Egypt.

RESEARCH HIGHLIGHTS: New variant IBDV which emerged in Egypt clustered with Chinese nVarIBDV.nVarIBDV spread subclinically across a wide geographic area.Mutation at 321 represents capsid's most exposed part, a defining feature.Antigenically modified vvIBDV still circulating in Egypt with typical lesions.

Protective effects of rabbit sacculus-derived antimicrobial peptides on SPF chicken against infection with very virulent infectious bursal disease virus.

Previous studies here have demonstrated that the rabbit sacculus rotundus-derived antimicrobial peptides (RSRP) could alter the intestinal mucosal immune responses in specific-pathogen-free (SPF) chickens, however, the protective effects of RSRP on chickens against infection remain questionable. In the present study, eighty SPF chickens were randomly divided into five groups and challenged with very virulent infectious bursal disease virus (vvIBDV) to determine the protective effects and its underlying mechanism of RSRP. Histopathology examination found that vvIBDV-infection caused severe damage in the bursa of Fabricius, especially the bursal lymphoid follicles underwent severe necrosis, depletion, hemorrhage, and edema. Unexpectedly, RSRP intervention significantly reduced the necrosis and depletion of lymphoid follicles in the vvIBDV-infected chickens. Moreover, RSRP treatment significantly decreased the expression of Bax (P < 0.01) as well as remarkably promoted the expression of Bcl-2 (P < 0.01), concomitantly alleviated the excessive apoptosis in the immune organs such as the bursa of Fabricius during vvIBDV infection. Notably, consistent with our previous reports that increased mast cell activation and degranulation in the bursa after vvIBDV infection, RSRP administration considerably reduced the mast cell density and the expression of tryptase, a marker for activated mast cells. Collectively, the present study indicates that rabbit sacculus rotundus-derived antimicrobial peptides could effectively protect the major immune organs including the bursa of Fabricius from the damage caused by vvIBDV infection, which provides the possibility and a promising perspective for the future application of antimicrobial peptides for poultry production.

Growth and replication of infectious bursal disease virus in the fish cell line as an experimental vaccine.

Recently, several attempts have been made to replace egg-based with cell-based vaccines to prevent and control Infectious Bursal Disease Virus (IBDV). This study aimed to evaluate a new fish cell line (M99) for culturing and replicating IBDV. After observing complete cytopathic effects (CPE) on the M99 cell line, virus titers were determined using the TCID50 test, and the presence of the virus was confirmed using an RT-PCR test. Subsequently, 135 broiler chickens (14 days old) were randomly divided into three equal groups for immune response measurements: G1: immunized with a commercial vaccine, G2: immunized with an experimental vaccine, and G3: control. Antibody responses, bursal index, and histopathological evaluations were examined on different days after immunization. Based on the results, CPE of the virus was noticeable from the first passage, becoming complete by the third passage. The infectious titer of the virus was log106.9. Antibody titer measured 21 days after immunization in both vaccinated groups were significantly differed from the control group (p < 0.05). The results obtained from examining the bursal index and histopathological evaluations showed no significant difference between the studied groups at different times. Overall, this research is the first report on the successful cultivation of infectious bursal virus on a permanent cell line of fish origin, with the advantages of tolerance to a wide temperature range (26-40 degrees Celsius). Therefore, this cell line has potential for use to attenuate, cultivate, and adapt other pathogens to cold temperatures in future studies.

Effects of ultra-filtration purification of infectious bursal disease virus on immune responses and cytokine activation in specific pathogen free chickens.

Purification is an important step in the production of viral vaccines that strongly affects product recovery and subsequent immune responses. The present study was carried out with the aim of improving the purification of infectious bursal disease virus (IBDV) by the tangential flow filtration (TFF) method. Then, the effect of the purified virus on the induction of immune responses against IBDV in specific pathogen free (SPF) chickens was investigated. The IBD07IR strain was propagated in embryonated SPF eggs. The virus was purified using a 100 kDa cassette. The quality of the recovered viruses was evaluated by titration. A total number of 60 SPF chickens were randomly divided into three groups (n = 20) and received the concentrated viral antigen, commercial live IBDV vaccine and phosphate-buffered saline at the age of 3 weeks by eye drop method. The bursa of Fabricius was examined histopathologically for possible changes. Sera were collected at 1-week intervals from day 0 until the end of 6 weeks after vaccination. The IBDV-specific antibody levels, induction of cell-mediated immunity and mRNA expression levels of cytokines were evaluated. The results showed that despite a relative raise in virus titer from 7.66 to 8.17 embryo infectious dose (EID)50 mL-1 following purification, both the purified IBDV and commercial vaccine are able to induce strong immune responses against the virus. Within a context of egg-based IBDV vaccine production, a single-step TFF can be applied for the relatively purification. This platform requires a further study in the selection of multiple membranes to optimize the operating conditions and final product.

The long noncoding RNA loc107053557 acts as a gga-miR-3530-5p sponge to suppress the replication of vvIBDV through regulating STAT1 expression.

Infectious bursal disease virus (IBDV) causes immunosuppression and high mortality in young chickens. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are important regulators during viral infection. However, detailed the regulatory mechanisms of lncRNA-miRNA-mRNA have not yet been described in IBDV infection. Here, we analysed the role of lncRNA53557/gga-miR-3530-5p/STAT1 axis in very virulent IBDV (vvIBDV) infection. Evidently upregulated expression of lncRNA53557 was observed in bursa of Fabricius and DT40 cells. Meanwhile, overexpression of lncRNA53557 promoted STAT1 expression and inhibited vvIBDV replication and vice versa, indicating that the upregulation of lncRNA53557 was part of the host antiviral defence. The subcellular fractionation assay confirmed that lncRNA53557 can be localized in the cytoplasm. Further, dual-luciferase reporter, RNA pulldown, FISH and RT-qPCR assays revealed that lncRNA53557 were directly bound to gga-miR-3530-5p and had a negative regulatory relationship between them. Subsequent mechanistic analysis showed that lncRNA53557 acted as a competing endogenous RNA (ceRNA) of gga-miR-3530-5p to relieve the repressive effect of gga-miR-3530-5p on its target STAT1, as well as Mx1, OASL, and ISG15, thereby suppressing vvIBDV replication. The study reveals that a network of enriched lncRNAs and lncRNA-associated ceRNA is involved in the regulation of IBDV infection, offering new insight into the mechanisms underlying IBDV-host interaction.

Development of a Highly Efficient CRISPR/Cas9-Mediated Herpesvirus of Turkey-Based Vaccine against Novel Variant Infectious Bursal Disease Virus.

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is an extremely contagious immunosuppressive disease that causes major losses for the poultry industry worldwide. Recently, the novel variant IBDV (G2d) has been highly prevalent in Korea, but the current vaccines against this very virulent IBDV have limited efficacy against this novel variant. To develop a vaccine against this variant IBDV, a recombinant virus designated rHVT-VP2 was constructed by inserting the IBDV (G2d) VP2 gene into herpesvirus of turkeys (HVT) using CRISPR/Cas9 gene-editing technology. The PCR and sequencing results obtained showed that the recombinant virus rHVT-VP2 was successfully constructed. Vaccination with rHVT-VP2 generated IBDV-specific antibodies in specific pathogen-free chickens starting from 2 weeks post-immunization. Seven days after the challenge, the autopsy results showed that the bursa atrophy rates of the rHVT-VP2, HVT, vaccine A, and positive control groups were 0%, 100%, 60%, and 100%, respectively, and the BBIX values were 1.07 ± 0.22, 0.27 ± 0.05, 0.64 ± 0.33, and 0.32 ± 0.06, respectively. These results indicate that rHVT-VP2 can provide 100% protection against a challenge with the IBDV (G2d), whereas vaccine A only provides partial protection. In conclusion, vaccination with the recombinant virus rHVT-VP2 can provide chickens with effective protection against variant IBDV (G2d).

Research Note: Characterization and phylodynamic analysis of new infectious bursal disease virus variants circulating in Argentina.

Infectious Bursal Disease is a highly contagious disease that affects young chickens and leads to significant economic losses. Its causal agent is a double-stranded RNA virus that, due to its high error rate during the replication process, gives rise to a constant generation of new virus variants. Until 2014, strains of Infectious Bursal Diseases Virus (IBDV) belonging to genogroup 4 predominated in Argentina, but there have been no reports since then regarding the circulating genogroups in poultry. In this study, 11 recent sequences of Argentine from the hypervariable region of VP2 protein (hvVP2) were analyzed to determine their genogroup, origin, evolution, and amino acid sequence. Samples from chickens showing signs of IBDV infection were collected, and the hvVP2 region was amplified using RT-PCR, followed by sequencing. The results indicated that the analyzed strains belong to genogroup 2, with an estimated evolutionary rate of 1.74 × 10-3 substitutions/site/year. It is speculated that the predominant group of sequences began to spread in Argentina around 2014 and had its origins in China. Another sample is related to strains from South Korea and is not closely linked to the main group. Furthermore, the predicted amino acid sequences show similarity to strains that can evade vaccine-induced immunity. These findings underscore the importance of active surveillance in poultry to mitigate losses caused by IBDV.

Advancement of Autogenous Vaccines in the Poultry Industry.

Autogenous vaccines, also known as "custom" vaccines, have become an essential instrument in the production veterinarian's toolbox for the control of emerging and evolving diseases. Autogenous vaccines require a reduced burden of U.S. Department of Agriculture licensing, making them rapidly accessible. Autogenous vaccines have made significant advancements in the ability to reduce disease within the poultry industry from a combination of several different advancements in regulation requirements, rapid and accurate diagnostic assessments, and improvements in manufacturing. The use of autogenous vaccines by poultry health professionals has also increased, and these custom-made products have been instrumental in combating diseases resulting from antigenic variants such as salmonellosis, colibacillosis, infectious coryza, infectious bursal disease, inclusion body hepatitis, viral enteritis, and viral arthritis and tenosynovitis.

Estudio recapitulativo- Avance de las vacunas autógenas en la industria avícola Las vacunas autógenas, también conocidas como vacunas "personalizadas, elaboradas de acuerdo con las necesidades del cliente" ("custom"), se han convertido en un instrumento esencial en el inventario de herramientas del veterinario de producción para el control de enfermedades emergentes y en evolución. Las vacunas autógenas requieren un procedimiento reducido para obtener la licencia por parte del Departamento de Agricultura de los Estados Unidos, lo que las hace rápidamente accesibles. Las vacunas autógenas han logrado avances significativos en la capacidad de reducir enfermedades dentro de la industria avícola gracias a una combinación de varios avances diferentes en los requisitos regulatorios, evaluaciones de diagnóstico rápidas y precisas y mejoras en la fabricación. También ha aumentado el uso de vacunas autógenas por parte de los profesionales de la salud avícola, y estos productos hechos a medida han sido fundamentales para combatir enfermedades resultantes de variantes antigénicas como la salmonelosis, la colibacilosis, la coriza infecciosa, la enfermedad infecciosa de la bolsa, hepatitis con cuerpos de inclusión, la enteritis viral y la artritis y tenosinovitis virales.

RNA-seq reveals role of cell-cycle regulating genes in the pathogenicity of a field very virulent infectious bursal disease virus.

Infectious bursal disease virus (IBDV) infection causes highly contagious and immunosuppressive disease in poultry. The thymus, serving as the primary organ for T cell maturation and differentiation, plays an important role in the pathogenicity of IBDV in the infected chickens. However, there are no reports on the molecular pathogenesis of IBDV in the thymus currently. The aim of the study was to elucidate the molecular mechanisms underlying the pathogenicity of a field very virulent (vv) IBDV strain NN1172 in the thymus of SPF chickens using integrative transcriptomic and proteomic analyses. Our results showed that a total of 4,972 Differentially expressed genes (DEGs) in the thymus of NN1172-infected chickens by transcriptomic analysis, with 2,796 up-regulated and 2,176 down-regulated. Meanwhile, the proteomic analysis identified 726 differentially expressed proteins (DEPs) in the infected thymus, with 289 up-regulated and 437 down-regulated. Overall, a total of 359 genes exhibited differentially expression at both mRNA and protein levels, with 134 consistently up-regulated and 198 genes consistently down-regulated, as confirmed through a comparison of the RNA-seq and the proteomic datasets. The gene ontology (GO) analysis unveiled the involvement of both DEGs and DEPs in diverse categories encompassing cellular components, biological processes, and molecular functions in the pathological changes in IBDV-infected thymus. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the host mainly displayed severely disruption of cell survival/repair, proliferation and metabolism pathway, meanwhile, the infection triggers antiviral immune activation with a potential emphasis on the MDA5 pathway. Network inference analysis identified seven core hub genes, which include CDK1, TYMS, MCM5, KIF11, CCNB2, MAD2L1, and MCM4. These genes are all associated with cell-cycle regulating pathway and are likely key mediators in the pathogenesis induced by NN1172 infection in the thymus. This study discovered dominant pathways and genes which enhanced our understanding of the molecular mechanisms underlying IBDV pathogenesis in the thymus.

The booster immunization using commercial vaccines effectively protect chickens against novel variants of infectious bursal disease virus (genotype A2dB1).

The novel variant IBDV (nVarIBDV, genotype A2dB1), characterized by bursal atrophy of fabricius and decreased lymphocytes, has been emerging on a large scale in Asia (including China) since late 2018. nVarIBDV is a new threat to the poultry industry, yet the currently licensed commercial vaccines, including the live viral vector vaccine, IBDV immune complex vaccine or VP2 subunit vaccine, are ineffective against nVarIBDV infection. In this study, specific-pathogen-free (SPF) chickens and broilers divided into 3 groups were vaccinated with the live viral vector vaccine, the VP2 subunit vaccine or the IBDV immune complex vaccine at 1 day-old, respectively. The SPF chickens received a secondary vaccination with the live B87 strain vaccine at 11-day-old. The bursa/body weight ratio, histopathology lesion of the bursa, and the differentiation between infected and vaccinated animals (DIVA) by qRT-PCR confirmed that the live viral vector vaccine or immune complex vaccine plus live B87 strain booster could provide at least 80% protection against the FJ2019-01 strain of nVarIBDV in SPF chickens. The broilers also received a secondary vaccination using a live W2512 G-61 strain vaccine at 14-day-old, and analyses showed that the VP2 subunit vaccine or immune complex vaccine plus the live W2512 G-61 strain booster also provided more than 80% protection against the FJ2019-01 strain of nVarIBDV. Unfortunately, the live viral vector vaccine plus live W2512 G-61 strain booster provided poor to moderate protection against FJ2019-01 in broilers. These findings suggest that combining commercial vaccines with rational booster immunization can effectively protect chickens against an nVarIBDV challenge.

Infectious bursal disease virus VP5 triggers host shutoff in a transcription-dependent manner.

Viruses have evolved intricate mechanisms to evade host antiviral responses and exploit cellular resources by manipulating the expression profile of host genes. During infection, viruses encode proteins with shutoff activity to globally inhibit host protein synthesis, which is an effective strategy for immune evasion. In this study, compelling evidence shows that infectious bursal disease virus (IBDV) infection triggers the suppression of host protein synthesis. Furthermore, using both in vitro and in vivo viral infection models, we have identified that IBDV specifically impedes the transcription of host genes via the shutoff activity of viral VP5, simultaneously conferring advantages to IBDV infection in these circumstances. The proposed mechanism suggests that VP5 competitively binds to RanBP1, disrupting the RanGDP/GTP gradient. This disruption interferes with cellular nucleocytoplasmic transport, impairing the nuclear import of proteins bearing nuclear localization signals. The nuclear transport of pivotal transcriptional regulatory factors, such as p65 and IFN regulatory factor 7, is also compromised, leading to the inhibition of pro-inflammatory cytokines and interferon expression. This newly discovered strategy employed by IBDV enables them to manipulate host gene expression, providing novel insights into how viruses evade host immune responses and establish infections.IMPORTANCEViruses manipulate host processes at various levels to regulate or evade both innate and adaptive immune responses, promoting self-survival and efficient transmission. The "host shutoff," a global suppression of host gene expression mediated by various viruses, is considered a critical mechanism for evading immunity. In this study, we have validated the presence of host shutoff during infectious bursal disease virus (IBDV) infection and additionally uncovered that the viral protein VP5 plays a pivotal role in inhibiting the overall synthesis of host proteins, including cytokines, through a transcription-dependent pathway. VP5 competitively binds with RanBP1, leading to disruption of the Ran protein cycle and consequently interfering with nucleocytoplasmic transport, which ultimately results in the suppression of host gene transcription. These findings unveil a novel strategy employed by IBDV to evade host innate immunity and rapidly establish infection. This study also suggests a novel supplement to understanding the pathway through which viruses inhibit host protein synthesis.

Evasion of maternal antibody protection by an IBDV Argentine variant.

Infectious bursal disease (IBD) is a viral disease that affects the ability of chickens to produce humoral immune responses. One way to prevent the disease is the passage of maternally derived antibodies (MDA) from dams to offsprings via the yolk. Despite sanitary measures, which include immunization with genogroup 1 (G1) vaccines, infections with IBDV genogroup 4 (G4) in young animals have been detected. The aim of this study was to determine whether a local IBDV isolate belonging to G4 could evade the immunity generated by MDAs. Twelve-day-old animals positive for MDA, were inoculated with G1 or G4 isolates or phosphate buffered saline (PBS) as a control. After 1 wk, the animals were sacrificed and the following parameters were evaluated: bursa-body (BB) ratio, viral load, and histologic damage in the bursa of Fabricius. Results showed that G4-infected animals had significant differences in the BB ratio compared to the PBS group. In addition, viral load was significantly higher in the G4 group than in the G1 group. Histologic damage in the bursa of Fabricius was detected only in G4-infected MDA chickens. Our results suggest that infection with G4 local isolate can circumvent the immunity generated by MDA and, furthermore, that G4 isolate does not differ in its pathogenicity from G1 isolate, which underlines the need to include variant strains in vaccine formulations to reduce potential losses caused by these viruses.

Development of egg yolk-based polyclonal antibodies and immunoprophylactic potential of antigen-antibody complex against infectious bursal disease.

A study conducted in the Faisalabad district sampled 50 cases across five IBD outbreaks, revealing an alarming 80 % infection rate among poultry. Our research focused on developing an immune complex (Antigen-antibody complex) with potential immunoprophylactic benefits to counter this formidable threat. Our study was based on producing egg yolk-derived polyclonal antibodies (IgY) targeting IBDV. Commercial layer birds were immunized with inactivated IBDV, yielding IgY antibodies extracted from their eggs exhibited substantially higher and more enduring antibody titers, with a geometric mean titer of 104. Further research involved the creation of an immune complex (ICx) where antigen was extracted from infected bursae tissues. The immunogenic response of ICx was assessed in poultry birds after a challenge with a virulent strain of IBD virus and compared to a conventional IBDV vaccine in poultry. Results revealed significantly higher and more enduring antibody titers induced by the ICx, offering enhanced protective immunity against the IBDV challenge, as evidenced by lower Bursa to bodyweight ratios in vaccinated birds.

Protective effects of a novel chimeric virus-like particle vaccine against virulent NDV and IBDV challenge.

Newcastle disease (ND) and infectious bursal disease (IBD) pose significant threats to the chicken industry, causing substantial economic losses. Currently, immunization through vaccination is the most effective strategy to prevent ND and IBD but currently used traditional vaccines, including inactivated or attenuated vaccines, face challenges in achieving a balance between immunogenicity and safety. To develop a green and efficient novel vaccine for ND and IBD, we developed a bivalent chimeric virus-like particle vaccine (ND-IBD cVLPs) displaying the ND virus (NDV) HN protein and the IBD virus (IBDV) VP2 protein based on the ND VLPs carrier platform and insect baculovirus expression system. This study aimed to evaluate the immunogenicity and protective efficacy of ND-IBD cVLPs in specific pathogen-free chickens. Chickens were immunized with 50 µg of purified ND-IBD cVLPs at 7 days old, boosted at 21 days old, and challenged at 42 days old. The results demonstrated that ND-IBD cVLPs stimulated highly effective hemagglutination inhibition antibody levels against NDV HN protein and enzyme-linked immunosorbent assay antibody levels against the IBDV VP2 protein. Furthermore, ND-IBD cVLPs provided complete protection against virulent NDV and IBDV challenges and mitigated pathological damage to the lung caused by NDV infection and the bursa of Fabricius caused by IBDV infection. These findings suggest that ND-IBD cVLPs hold promise as a safe and efficient novel vaccine candidate for the effective prevention of ND and IBD, extending the development of a foreign protein delivery platform of ND VLPs.

Molecular epidemiology of infectious bursal disease virus in the Near East and Persian Gulf regions.

RESEARCH HIGHLIGHTS: Different field IBDVs were found to circulate in the Near and Middle East.Multiple atypical genotypes (A3B1, A4B1, A6B1) were found to circulate extensively.Traditional very virulent IBDVs (A3B2) were a minority of the detected strains.Viral exchanges can be hypothesized between the region and different continents.

Development and evaluation of a bivalent vaccine based on recombinant newcastle disease virus expressing infectious bursal disease virus VP2L-CH3-CH4 in SPF chickens.

Newcastle disease (ND) and infectious bursal disease (IBD) are two viral infectious diseases that are extremely damaging to the poultry industry and are widespread throughout the world. It is necessary to develop a safe and effective vaccine against IBD and ND because vaccination is an effective preventive measure. It has been discovered that recombinant proteins expressed by an expression system in which a fragment of mammalian Immunoglobulin G (IgG) Fragment crystallizable (Fc) is linked to a segment of a gene have antibody-like properties that increase the exogenous protein's serum half-life. Heavy chain constant region 3 and heavy chain constant region 4 (CH3-CH4) of Avian Immunoglobulin Y (IgY) is structurally very similar to mammalian Ig G Fc. In this study, a bivalent vaccine rClone30-VP2L-CH3-CH4-GMCSF was developed by using NDV rClone30-chGM-CSF vector to produce VP2L-CH3-CH4 fusion protein. The vaccine has been given to 14-day-old specific pathogen free (SPF) free chickens to test whether it has the potential to prevent IBD and ND. Anti-IBDV and anti-NDV antibody levels in serum were evaluated using ELISA and HI, respectively, and the contents of CD4+ T, CD8+ T, and B cells in leukocytes were determined via flow cytometry. The contents and mRNA transcription levels of four inflammatory factors, IL-1ß, IL-4, IFN-γ and chGM-CSF, were detected by ELISA and real-time PCR respectively. The results showed that after vaccination with the rClone30-VP2L-CH3-CH4-GMCSF vaccine, the levels of anti NDV and anti IBDV antibodies in chickens were significantly higher than those of the rClone30 vaccine and commercial vaccines. Meanwhile, the contents and transcription levels of inflammatory factors in chickens inoculated with rClone30-VP2L-CH3-CH4-GMCSF were significantly increased, and the proliferation response of B cells, CD4+ and CD8+ T cells was also stronger. However, the rClone30-VP2L-CH3-CH4-GMCSF vaccine had no significant advantage over the rClone30-VP2L-GMCSF vaccine in any of the above-mentioned features. In summary, rClone30-VP2L-CH3-CH4-GMCSF can stimulate the body to produce a stronger immune response, showing its potential to be considered as vaccine against IBD and ND, but the addition of CH3-CH4 did not improve the vaccine's immune effect as expected. The research lays the foundation for developing vaccines for other infectious viral diseases and avoids a unrealistic vaccine optimization method.

Genetic and pathogenic characterizations of a naturally occurring reassortant and homologous recombinant strain of the classical infectious bursal disease virus re-emerging in chickens in southern China.

Infectious bursal disease (IBD) classical virus strain (cIBDV) can cause morbidity and mortality in young chickens with severe long-term immunosuppression. However, since the emergence and widespread prevalence of very virulent strain (vvIBDV) in China from 1991, reports of cIBDV have become rare. A novel reassortant and recombinant strain GXYL211225 (genotype A1aB1a) with segment A originating from the classical strain (A1a) and segment B from the attenuated vaccine strain (B1a) was characterized in the study. Notably, segment A resulted from recombination between the cIBDV strains 150127-0.2 and Faragher52-70, expressing as a backbone from 150127-0.2, where a fragment located at the position of nucleotide (nt) 519-1 410 was replaced by the corresponding region of Faragher52-70. The infection of GXYL211225 caused mortality in SPF chicken embryos, despite lacking the critical amino acid (aa) residues 253H, 279 N and 284A associated with the cellular tropism, and induced significant cytopathic effect (CPE) on a wide range of cells, confirming its natural cell-adapted character. Furthermore, the challenge experiment of GXYL211225 was performed on the commercial Three-yellow chickens of 4-week-old, and with the vvIBDV HLJ-0504-like strain NN1172 and the novel variant (nv) IBDV strain QZ191002 as the comparison. All the challenged birds experienced reduced body-weight gain. QZ191002 infected birds showed no obvious clinical symptoms or mortality, while those of NN1172 and GXYL211225 showed typical IBD symptoms and resulted in 20% (2/10) and 10% (1/10) of mortality rates, respectively. At 7 days post-challenge (dpc), the damages of bursal of Fabricius (BF) varied among groups, with NN1172 causing the most severe lesions, followed by GXYL211225, and then QZ191002. It was also found that the pathogenicity was correlated positively with the viral load, aligning with the histopathological severity in BF. The study confirms the rapid and diverse evolution of the re-emerged classical strains in the field and emphasizes the need to monitor the changes of IBDV on both the genetic and pathogenic aspects for the effective control of the disease.

First Detection and Molecular Characterization of Novel Variant Infectious Bursal Disease Virus (Genotype A2dB1b) in Egypt.

Infectious bursal disease (IBD) is an immunosuppressive disease causing significant damage to the poultry industry worldwide. Its etiological agent is infectious bursal disease virus (IBDV), a highly resistant RNA virus whose genetic variability considerably affects disease manifestation, diagnosis and control, primarily pursued by vaccination. In Egypt, very virulent strains (genotype A3B2), responsible for typical IBD signs and lesions and high mortality, have historically prevailed. The present molecular survey, however, suggests that a major epidemiological shift might be occurring in the country. Out of twenty-four samples collected in twelve governorates in 2022-2023, seven tested positive for IBDV. Two of them were A3B2 strains related to other very virulent Egyptian isolates, whereas the remaining five were novel variant IBDVs (A2dB1b), reported for the first time outside of Eastern and Southern Asia. This emerging genotype spawned a large-scale epidemic in China during the 2010s, characterized by subclinical IBD with severe bursal atrophy and immunosuppression. Its spread to Egypt is even more alarming considering that, contrary to circulating IBDVs, the protection conferred by available commercial vaccines appears suboptimal. These findings are therefore crucial for guiding monitoring and control efforts and helping to track the spread of novel variant IBDVs, possibly limiting their impact.