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.

Novel variant infectious bursal disease virus diminishes FAdV-4 vaccination and enhances pathogenicity of FAdV-4.

Infectious bursal disease virus (IBDV) caused an acute and highly contagious infectious disease characterized by severe immunosuppression, causing considerable economic losses to the poultry industry globally. Although this disease was well-controlled under the widely use of commercial vaccines in the past decades, the novel variant IBDV strains emerged recently because of the highly immunized-selection pressure in the field, posting new threats to poultry industry. Here, we reported novel variant IBDV is responsible for a disease outbreak, and assessed the epidemic and pathogenicity of IBDV in this study. Moreover, we constructed a challenge model using Fowl adenovirus serotype 4 (FAdV-4) to study on the immunosuppressive effect. Our findings underscore the importance of IBDV surveillance, and provide evidence for understanding the pathogenicity of IBDV.

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.

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.

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.

Virus-like Particle Vaccines of Infectious Bursal Disease Virus Expressed in Escherichia coli Are Highly Immunogenic and Protect against Virulent Strain.

OBJECTIVES: Infectious bursal disease virus (IBDV) is a highly contagious, acutely infectious agent that causes immunosuppression in chickens. We expressed IBDV VP2 proteins in Escherichia coli (E. coli) to develop an effective virus-like-particles (VLPs) vaccine and evaluated its immunogenicity. METHODS: The VLPs produced in E. coli were used as an immunogen mixed with a water-in-mineral-oil adjuvant (MontanideTM ISA 71 VG, ISA 71 RVG) or a white oil (7#) adjuvant. VLPs without an adjuvant, commercial subunit vaccine, inactivated vaccine, and attenuated vaccine were used as controls. These test vaccines were intramuscularly injected into 19-day-old SPF chickens, which were challenged with the IBDV virulent strain at 30 days after vaccination. RESULTS: The adjuvants boosted antibody production, and the adjuvant groups (except white oil) produced higher antibody levels than the non-adjuvanted controls and the commercial vaccine groups. In terms of cellular immunity, the VLPs plus adjuvant combinations produced higher levels of cytokines, IL-2, IL-4, and IFN-γ than the controls. CONCLUSION: IBDV VLPs plus the ISA 71 RVG adjuvant can be used as an optimal vaccine combination for improving the immune efficacy of IBD subunit vaccines, which can protect against the virulent strain.

Development of a One-Step Real-Time TaqMan Reverse Transcription Polymerase Chain Reaction (RT-PCR) Assay for the Detection of the Novel Variant Infectious Bursal Disease Virus (nVarIBDV) Circulating in China.

The novel variant IBDV (nVarIBDV, especially genotype A2dB1) mainly affects broilers in China. It causes an infection characterized by the atrophy of the bursa, a decrease in the level of lymphocytes, proliferation of fibrous tissue around the follicle, and severe atrophy of the follicle in the bursa. Poultry vaccinated with live IBDV vaccines do not have the challenge present with bursa atrophy, which is misdiagnosed for nVarIBDV because of the lack of other gross clinical symptoms. The present study sought to explore the potential and reliability of the real-time TaqMan analysis method for the detection and discrimination of the nVarIBDV genotype from that of the non-nVarIBDV, especially in live vaccine strains. This method will help monitor vaccinated poultry to control and manage infection with the nVarIBDV IBDVs. The nucleotide polymorphism in the 5'-UTR region and the vp5/vp2 overlapping region of the segment A sequences of IBDV were used to establish a one-step real-time TaqMan reverse transcription polymerase chain reaction (RT-PCR) method in this study. The results showed that the method accurately distinguished the nVarIBDV and non-nVarIBDV strains (especially live vaccine strains), and there were no cross-reactions with the infectious bronchitis virus (IBV), Newcastle disease virus (NDV), avian influenza virus (AIV), infectious laryngotracheitis virus (ILTV), fowlpox virus (FPV), Mycoplasma gallisepticum (M. gallisepticum), Mycoplasma synoviae (M. synoviae), and IBDV-negative field samples. The method showed a linear dynamic range between 102 and 107 DNA copies/reaction, with an average R2 of 0.99 and an efficiency of 93% for nVarIBDV and an average R2 of 1.00 and an efficiency of 94% for non-nVarIBDV. The method was also used for the detection of 84 clinical bursae of chickens vaccinated with the live vaccine. The results showed that this method accurately distinguished the nVarIBDV and non-nVarIBDV strains (vaccine strains), compared with a strategy based on the sequence analysis of HVRs at the vp2 gene or the reverse transcription PCR (RT-PCR) for the vp5 gene. These findings showed that this one-step real-time TaqMan RT-PCR method provides a rapid, sensitive, specific, and simple approach for detection of infections caused by nVarIBDV and is a useful clinical diagnostic tool for identifying and distinguishing nVarIBDV from non-nVarIBDV, especially live vaccine strains.

Live IBD vaccine exacerbates disease and pathological effects of Asian lineage H9N2 LPAIV in chickens.

Avian influenza H9N2 is one of the most commonly circulating viruses in numerous Egyptian poultry farms. The Asian lineage H9N2 exhibits an immunosuppressive effect, and its pathogenicity is amplified when it co-infects with other pathogens, especially with the immunosuppressive infectious bursal disease virus (IBDV), resulting in increased mortality rates. Both vaccines and field infection can exacerbate the pathogenicity of H9N2, particularly in the bursa of Fabricius, causing more significant lymphoid depletion. To comprehend the impact of the IBD vaccine on the viral and pathogenic effect of H9N2 infection in specific pathogen-free chicks (SPF), the experiment was designed as four groups; group 1 served as the negative control, group 2 received (228E) IBD vaccine, group 3 was challenged with H9N2, and group-4 was vaccinated by the IBD vaccine then challenged with H9N2. The clinical signs, relative immune organs weights and histopathological lesion scores were recorded. The tracheal and cloacal H9N2 viral shedding were also measured. Group 4 exhibited a significant decrease (P ≤ 0.05) in the relative bursal weight and an increase in the bursal lesion score when compared with groups 1 and 3 at 4 and 8 days post-challenge (dpc). The tracheal lesion score of group-4 recorded a significant increase when compared with groups 1 and 3. The renal lesion score of group 4 achieved a significant increase when compared with 1 and 3 at 8 dpc. Also, group 4 recorded a significant increase in H9N2 shedding in comparison with groups 1 and 3. Consequently, our study concluded that routine vaccination with the IBD intermediate plus vaccine exacerbates the silent infection of H9N2 resulting in outbreaks.

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.

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.

Efficacy of multivalent recombinant herpesvirus of turkey vaccines against high pathogenicity avian influenza, infectious bursal disease, and Newcastle disease viruses.

Vaccines are an essential tool for the control of viral infections in domestic animals. We generated recombinant vector herpesvirus of turkeys (vHVT) vaccines expressing computationally optimized broadly reactive antigen (COBRA) H5 of avian influenza virus (AIV) alone (vHVT-AI) or in combination with virus protein 2 (VP2) of infectious bursal disease virus (IBDV) (vHVT-IBD-AI) or fusion (F) protein of Newcastle disease virus (NDV) (vHVT-ND-AI). In vaccinated chickens, all three vHVT vaccines provided 90-100% clinical protection against three divergent clades of high pathogenicity avian influenza viruses (HPAIVs), and significantly decreased number of birds and oral viral shedding titers at 2 days post-challenge compared to shams. Four weeks after vaccination, most vaccinated birds had H5 hemagglutination inhibition antibody titers, which significantly increased post-challenge. The vHVT-IBD-AI and vHVT-ND-AI vaccines provided 100% clinical protection against IBDVs and NDV, respectively. Our findings demonstrate that multivalent HVT vector vaccines were efficacious for simultaneous control of HPAIV and other viral infections.

Circular RNA circAKIRIN2 participates in the process of stress-induced immunosuppression affecting immune response to infectious bursal disease virus vaccine in chicken.

At present, stress-induced immunosuppression is still a hidden threat that leads to immunization failure and outbreaks of poultry diseases, and causes huge economic losses to the modern poultry industry. However, the molecular mechanisms of stress-induced immunosuppression affecting viral vaccine immunity are still poorly understood. Here, we identified circAKIRIN2 as a conserved circular transcript in chicken, and explored its expression patterns in different immune states by quantitative real-time PCR (qRT-PCR), then conducted bioinformatics analysis. The results showed that circAKIRIN2 actively participated in the process of stress-induced immunosuppression affecting the immune response to infectious bursal disease virus (IBDV) vaccine. The key time points for circAKIRIN2 involving in the process were 2 day post immunization (dpi), 5 dpi, and 28 dpi, especially at the acquired immune stage. The important tissues that responded to the process included the heart, liver, and lung, all of which changed significantly. In addition, circAKIRIN2 as a competing endogenous RNA (ceRNA) sponging zinc finger and BTB domain containing 20 (ZBTB20) was a potential molecular mechanism for regulating immune functions in the process. In conclusion, circAKIRIN2 is a key regulatory factor for stress-induced immunosuppression affecting the IBDV vaccine immune response, and this study can provide a new perspective for exploring the molecular regulatory mechanisms of stress-induced immunosuppression affecting immune response.

PLGA nanoparticle with Amomum longiligulare polysaccharide 1 increased the immunogenicity of infectious bursal disease virus VP2 protein.

1. The purpose of this study was to create ALP1-VP2-PLGA nanoparticle (AVPN) and to study the immunogenicity of AVPN. AVPN was prepared and observed by scanning and transmission electron microscopies.2. Chickens were divided into five groups and vaccinated with normal saline, VP2 protein, ALP1 and VP2 protein, AVPN or PLGA, respectively. After 28 days, the immune organ indexes were calculated; specific antibody levels in blood were detected by enzyme-linked immunosorbent assay (ELISA). Additionally, the spleen and bursa of Fabricius were determined by HE staining, immunological cytokine mRNA levels in bursa of Fabricius were detected by qPCR andchicken body weight was determined.3. The results indicated that AVPN was a spherical nanoparticle with a diameter of about 85 nm. It increased bursal indexes and IBDV-specific antibody levels and promoted the expression of IL-2 mRNA in blood and TNF-α and IgG mRNA in bursa of Fabricius. This promoted growth.4. This study suggested that AVPN can increase immunogenicity of VP2 protein, and it could possibly be used as an IBDV subunit vaccine.

Development of a recombinant adenovirus-vectored vaccine against both infectious hematopoietic necrosis virus and infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss).

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are typical pathogens of rainbow trout Oncorhynchus mykiss, and the concurrent infection of the two viruses is very common among modern trout hatcheries, which has caused huge economic losses to the rainbow trout farming industry. To prevent and control the spread of IHNV and IPNV in juvenile trout simultaneously, in this study a bivalent recombinant adenovirus vaccine with IHNV Glycoprotein (G) and IPNV VP2 genes was developed. After immunizing juvenile trout with this bivalent vaccine via the immersion route, the expression levels of IHNV G and IPNV VP2 and the representative immune genes in vaccinated and control rainbow trout were tested to evaluate the correlation of immune responses with the expression of viral genes. The neutralizing antibody level induced by this bivalent vaccine as well as the protection efficacy of the vaccine against IHNV and IPNV was also evaluated. The results showed that IHNV G and IPNV VP2 were successfully expressed in juvenile trout, and all the innate and adaptive immune genes were up-regulated. This indicated that the level of the innate and adaptive immune responses were significantly increased, which might be induced by the high expression of the two viral proteins. Compared with the controls, high levels of neutralizing antibodies against IHNV and IPNV were induced in the vaccinated trout. Besides, the bivalent recombinant adenovirus vaccine showed high protection rate against IHNV, with the relative percent survival (RPS) of 81.25%, as well as against IPNV, with the RPS of 78.95%. Taken together, our findings clearly demonstrated that replication-defective adenovirus can be developed as a qualified vector for fish vaccines and IHNV G and IPNV VP2 were two suitable antigenic genes that could induce effective immune protection against these two pathogens. This study provided new insights into developing bivalent vectored vaccines and controlling the spread of IHNV and IPNV simultaneously in juvenile trout.

Comparative Safety, Immunogenicity, and Efficacy of CEF Cell-Based and DF-1 Cell Line Adapted Infectious Bursal Disease Vaccines in Specific-Pathogen-Free Chickens.

Infectious bursal disease (IBD) is an immunosuppressive and economically important disease of young chickens caused by infectious bursal disease virus (IBDV). The National Veterinary Institute (Bishoftu, Ethiopia) produces intermediate IBDV vaccine using primary chicken embryo fibroblast (CEF) cells, a method with technical and economical cumbersome. This study assessed the safety, immunogenicity, and efficacy of DF-1 cell line-adapted IBDV LC-75 vaccine strain in reference to the CEF-based vaccine. Confluent monolayer of DF-1 cells was infected with IBDV and cells with cytopathic effects were passaged until 3rd passage. Viral growth was confirmed using a one-step RT-PCR targeting IBDV VP2 gene. Viral titer increased from 1st passage through 3rd passage. Safety was assessed in 30 specific-pathogen-free chickens (15 chickens/group) injected with 10-fold field dose of each vaccine intraocularly and monitored for 21 days. For immunogenicity and efficacy, 60 specific-pathogen-free chickens were grouped into 3 (20 chickens/group). First and 2nd group received DF-1 cell and CEF-based IBDV vaccines, respectively. The 3rd group served as unvaccinated control. Antibody response was measured using iELISA. Chickens were challenged 4 weeks postvaccination with very virulent IBDV (vvIBDV) intraocularly and followed-up for 10 days. Vaccination did not cause any adverse reactions during the 21 days of follow-up. In addition, both vaccines induced higher antibody titer 14 and 24 days-post-vaccination as compared to unvaccinated controls (p < 0.05). Moreover, DF-1 and CEF-based IBDV LC-75 vaccines rendered a complete protection against vvIBDV. Contrarily, morbidity and mortality in unvaccinated chickens was 50% and 30%, respectively. The results indicated that DF-1 and CEF cell-based IBDV vaccines are comparably immunogenic and efficacious. Therefore, DF-1 cell-line can be considered an affordable and convenient alternative to the CEF-based approach. The suitability of DF-1 cells to grow other IBDV strains and safety of these vaccines on bursa of Fabricius should further be investigated.

Commercial vaccines used in China do not protect against a novel infectious bursal disease virus variant isolated in Fujian.

BACKGROUND: Since 2018, atrophy of the bursa has been found among vaccinated chickens with high antibody titres against infectious bursal disease virus (IBDV) in Fujian, China, suggesting poor vaccine efficacy against circulating IBDV strains. METHODS: Novel IBDV strains were isolated, and vp2 and vp1 genes were sequenced and used to carry out phylogenetic analysis. Pathogenicity was investigated using 21-day-old specific pathogen-free (SPF) chickens. In addition, the effectiveness of current commercial vaccines used in China was evaluated against the isolated novel IBDV strains. RESULTS: Six IBDV isolates were successfully obtained, which formed an independent cluster and belonged to genotype A2dB1, based on phylogenetic analysis of the vp2 and vp1 genes. The pathogenicity of the novel IBDV FJ2019-01 isolate in 21-day-old SPF chickens was characterised by severe atrophy of the bursa and a largely decreased number of lymphocytes, atrophy of the follicle and broadening of mesenchyme in the bursa 3-23 days after infection. Unfortunately, all vaccinated chickens with high antibody titres against IBDV also developed atrophy and largely decreased lymphocytes in the bursa, as in the unvaccinated birds challenged with FJ2019-01. Furthermore, high viral loads of FJ2019-01 were detected in the bursa of all vaccinated chickens. CONCLUSIONS: These findings suggest that current commercial IBDV vaccines used in China did not provide protection against novel IBDV variants.

Evaluation of five circulating strains of variant infectious bursal disease virus (varIBDV) for their immunogenicity as broiler breeder vaccines and protective efficacy in neonatal broiler chicks.

The majority of infectious bursal disease virus (IBDV) strains circulating in the broiler chicken industry in Canada are variant strains (varIBDV). Despite high levels of maternally derived antibodies (MtAb), the circulating varIBDVs can establish infection and cause severe immunosuppression in broiler chicks. The objective of this study was to evaluate circulating varIBDVs as broiler breeder vaccine candidates and investigate their protective efficacy against varIBDV challenge in their progeny chicks. Six groups of breeders (20 females/group) were vaccinated with varIBDV strains, SK09, SK10, SK11, SK12, and SK13 or saline at the age of 13 weeks and antibody response was determined by ELISA at 3-7-, and 20- weeks post-vaccination. We also included commercial chicks for the comparison. Results showed that SK-09 is the most antigenic strain, followed by SK-10, SK-12, and SK-13. In contrast, SK-11 showed the lowest antibody response, and over time, antibody titers steadily decreased. Eggs from breeders were collected at 21-week post-vaccination and incubated to produce their respective progenies. The serum antibody titer in day-old chicks showed a successful MtAb transfer. Progeny chicks (n = 40/group) were orally challenged with varIBDV-SK-09 strain at 6 days of age and serum antibody titer (19 d and 35 d of age), bursa to body weight ratio (19 d and 35 d of age), bursal viral load (9 d and 19 d of age) was examined to assess the protection against IBDV. Following the challenge, we found a significant increase in the antibody titers in MtAb-free and commercial vaccine groups than in the varIBDV groups, both at 19 d and 35 d of age. The BBW ratio and viral load data indicated a significant homologous and heterologous protection against varIBDV-SK-09 challenge by SK-09 and SK-10 MtAbs, respectively. Overall, this study demonstrated the feasibility of developing breeder vaccines using circulating varIBDV as candidate vaccine antigens.

Characterization and pathogenicity of infectious bursal disease virus in Southern China.

Infectious bursal disease virus (IBDV) is a widespread pathogen that induces immunosuppression in 3 to 6-wk-old chickens, casuing great threaten to the poultry industry worldwide. Previously, the very virulent IBDV (vvIBDV) was mainly prevalent in China. In recent years, the novel variant IBDV (nvIBDV) occurred in China. In this study, we isolated 30 IBDV strains of IBDV from vaccinated chicken flocks in 8 provinces of southern China. Among these isolates, vvIBDV group (13/30) and nvIBDV group (17/30) were identified according to the genome sequencing and phylogenic analysis. Moreover, HB2021-5 and GD2021-17 have pathologic characteristics with severe bursal lesions, as evidenced by necrosis, depletion of lymphocytes, and follicle atrophy. Our findings provide an important reference for understanding the epidemiological status and the evolution of IBDV.

An inactivated vaccine against infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss).

Infectious pancreatic necrosis virus (IPNV), belonging to the genus Aquabirnavirus within the family Birnaviridae, causes huge economic loss to the global salmonid industry every year. Recently, outbreaks of disease caused by genogroup I IPNV were found in many rainbow trout (Oncorhynchus mykiss) farms worldwide. An inactivated vaccine was prepared using a genogroup I IPNV isolate with an optimized procedure as incubation with ß-propanolactone (BPL) at the final concentration of 0.5% at room temperature for 48 h. The inactivated vaccine was used to immunize rainbow trout, and the protection efficiency was evaluated by viral loads determination, immune-related genes quantification, and neutralizing antibody tests. The viral loads in immunized rainbow trout were significantly decreased and the strongest antiviral effect was observed on 30 days post-immunization (d.p.i). The expression of innate immune-related genes IFN-1, and Mx-1 genes were significantly up-regulated on 3, 7, and 15 d.p.i (p < 0.05), and adaptive immune-related genes CD4, CD8, and IgM genes were significantly up-regulated on 15 and 30 d.p.i (p < 0.05). Neutralizing antibodies were firstly detected on 30 d.p.i and the highest titer was observed on 45 d.p.i, which began to decrease on 60 d.p.i, but was still significantly higher than that in negative control fish. The results indicated that the vaccine prepared in this study could stimulate the non-specific and specific immune response and provide significant immune protection to the vaccinated rainbow trout.

A novel inactivated bivalent vaccine for chickens against emerging hepatitis-hydropericardium syndrome and infectious bursal disease.

The emerging hepatitis-hydropericardium syndrome (HHS) caused by the novel genotype of fowl adenovirus 4 (FAdV-4) and the infectious bursal disease (IBD) caused by the infectious bursal disease virus (IBDV) are important avian diseases, both cause huge economic losses to the poultry industry. Therefore, it is necessary to develop an efficient and convenient FAdV-4/IBDV bivalent vaccine to prevent the spread of FAdV-4 and IBDV infections. Given that VP2 is the main structural protein and protective antigen of IBDV, we constructed a recombinant FAdV-4 expressing IBDV VP2 in our previous study. In the current study, an inactivated bivalent FAdV-4/IBDV vaccine was developed from the recombinant strain. The inactivated bivalent vaccine elicited effective and specific neutralizing antibodies against both FAdV-4 and IBDV in specific-pathogen-free chickens. Furthermore, the novel vaccine not only protected chickens from death caused by FAdV-4 and the very virulent IBDV (vvIBDV) infection, but also ameliorated target organ damage and reduced viral load. The FAdV-4-vectored vaccine developed in this study provides new options for the development of avian polyvalent inactivated vaccines and is a powerful tool for the prevention of both emerging HHS and IBD.