Live Infectious Bursal Disease Virus Research Articles

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.

Efficacy of different live infectious bursal disease vaccines on antibodies to infectious bursal disease virus and Newcastle disease vaccine La Sota in ISA brown chicks

Aim: In this study, the efficacy of five commercial live infectious bursal disease (IBD) vaccines on antibody (Ab) decay and response to a very virulent IBD virus (vvIBDV) and Newcastle disease (ND) vaccine La Sota in ISA Brown chicks were assessed. Methods: Seven groups of chickens (A, B, C, D, E, F, and G) comprising 50 chicks each were used for the study. Groups A, B, C, D, and E were vaccinated with Bur-706, MB-Strain, B87-Strain, Bursa-B2K, and HIPRA live IBD vaccines, respectively, at 14 and 28 days of age (doa), and challenged with a vvIBDV at 35 doa. Groups F and G served as positive and negative controls, respectively. At 42 doa, all groups were vaccinated with ND vaccine La Sota. Blood was collected at 1, 7, 14, 21, 28, 35, 42, and 49 doa, and serum was harvested. The serum was analyzed for IBD virus (IBDV) Ab titres using enzyme-linked immunosorbent assay (ELISA) and ND Ab titres using a haemagglutination inhibition (HI) test. Results: Results revealed significantly (p < 0.05) higher ELISA IBDV Ab titres in groups A to E than in F from 21 to 49 doa, with the highest in group D. At 49 doa, there was significantly (p < 0.05) higher HI Ab titre in groups A to E than in F with the highest in group D. In conclusion, the live IBDV vaccines were immunogenic following vaccination. The vaccines decreased the decay of IBDV Ab and mitigated the decreased response to ND vaccine La Sota in the chicks following the vvIBDV challenge, with more effects induced by Bursa-B2K. Conclusion: The live vaccines (Bur-706, MB-Strain, B87-Strain, Bursa-B2K, and HIPRA) were immunogenic following vaccination.

In ovo application of a live infectious bursal disease vaccine to commercial broilers confers proper immunity

ABSTRACT Infectious bursal disease (IBD) is an economically important disease of young chickens caused by the Avibirnavirus infectious bursal disease virus (IBDV). Besides biosecurity, vaccination is the most important measure for IBDV control. Sufficient levels of maternally derived antibodies (MDA) protect against early challenge and also interfere with the take of live conventional vaccines. Recently, the field surveys conducted in four countries, published by Ashash, U., Noach, C., Perelman, B., Costello, C., Sansalone, P., Brazil, T. & Raviv, Z. [(2019). In ovo and day of hatch application of a live infectious bursal disease virus vaccine to commercial broilers. Avian Diseases, 63, 713–720] using the MB-1 vaccine strain by in ovo application or sub-cutaneous route at the day of hatch seem to conflict with the rule that very early application of a conventional live vaccine in birds with significant levels of MDA has very little chance of a successful immune response. An in ovo vaccination-challenge controlled experiment with MB-1 vaccine was performed using commercial broilers with high levels of MDA against IBDV and a vvIBDV challenge at 22 or 36 days of age. Clinical signs, bursa-bodyweight ratios, histology, serology, RT–PCR, Sanger- and deep sequencing were used to study the efficacy and safety of the in ovo-applied MB1 vaccine in comparison to an established immuno-complex vaccine. The study findings confirmed that the in ovo application of the live MB-1 vaccine in commercial broilers was successful and induced full protection against a vvIBDV challenge at 22 and 36 days of age, demonstrated by the bursa lesion score and qPCR and IBDV genotyping. Comparable to the field studies, a delayed viral replication of 2–3 weeks, following the in ovo administration of the MB1 vaccine, was observed.

A field study on the evaluation of day-of-hatch and in grow-out application of live infectious bursal disease virus vaccine in broiler chickens

Infectious bursal disease (IBD) is an acute, highly contagious, economically important disease of young chickens caused by Avibirnavirus, the infectious bursal disease virus (IBDV). The causative virus is highly resilient in poultry environments and vaccination is the most effective measure for IBDV control. However, the susceptibility of highly attenuated IBDV vaccine strains to neutralization by maternally derived antibodies (MDA) and overwhelming virulence of partly attenuated strains have limited the application of conventional live IBDV vaccines in pre- and posthatch chicks. Nevertheless, preliminary data have raised questions about the validity of this prevailing dogma. India is an IBD endemic country and the disease causes sizeable economic losses in the sector. To evaluate the feasibility of application of live IBDV vaccine strain, the IBDV MB-1, to the maternally immunized day-of-hatch chicks in Indian production environment, 4 large-scale field trials have been conducted. The 4 trials have measured the relative safety, IBDV immunization parameters, and production performances of MB-1 vs. the established live and immune complex IBDV vaccines in a variety of commercial broiler systems. The overall health and production performances in all 4 trials have been better in the MB-1 groups. The results challenge the prevailing notion that live IBDV strains may be neutralized or break through maternal immunity and induce permanent damage to the young broiler chick's immune response. A delayed replication phenomenon following parenteral administration of the live IBDV vaccine strain has been observed, while the delayed replication mechanism remains to be elucidated. This study warrants further research on the molecular mechanism of live IBDV vaccine strain, MB-1, and its interaction with the chicken immune system.

Efficacy of a novel in ovo-attenuated live vaccine and recombinant vaccine against a very virulent infectious bursal disease virus in chickens.

Infectious bursal disease (IBD) causes severe economic damage to the poultry industry worldwide. To prevent IBD virus (IBDV) infection, live virus vaccines have been widely used in chickens having wide-ranging levels of maternally derived antibodies. But, the risks of infection with other pathogens because of lesions related to atrophy of the bursa of Fabricius in vaccinated chickens are a concern. To resolve the problems, a recombinant turkey herpesvirus (HVT) vaccine expressing IBDV-VP2 protein (rHVT-IBD) has been developed. However, the induction of neutralizing antibodies by rHVT-IBD against a virulent IBDV might be delayed compared with that by the live IBD vaccine, leading to the high risks of IBDV infection for young chickens. To find the best selection of IBDV vaccine for the onset of immunity, we examine the protective efficacy of a novel in ovo-attenuated live IBDV (IBD-CA) vaccine and the rHVT-IBD vaccine in young chickens challenged with a very virulent IBDV (vvIBDV) strain. We show that the protective efficacy of IBD-CA vaccine was higher than that of the rHVT-IBD vaccine in 14-day-old chickens challenged with the vvIBDV strain, leading to the risk of IBDV infection for young chickens when vaccinated with rHVT-IBD. Our results suggest that farmers should select the best vaccines to maximize vaccine efficacy in consideration of the vaccine characteristics, prevalence levels of IBDV in the areas, and initial MDA levels of the chickens since the attenuated live and recombinant vaccines play a role in the different vaccine efficacies.

In Ovo and Day of Hatch Application of a Live Infectious Bursal Disease Virus Vaccine to Commercial Broilers.

Infectious bursal disease (IBD) is an economically important disease of young chickens caused by an Avibirnavirus, the infectious bursal disease virus (IBDV). The causative virus is highly resilient in poultry environments and vaccination is the most effective measure for IBDV control. However, both the suspected neutralization of highly attenuated strains by maternal antibodies and the assumed virulence of partly attenuated strains have limited the implementation of conventional live IBDV vaccine strains in pre- and posthatch chicks. Nevertheless, preliminary data have raised questions about the validity of this prevailing dogma. To investigate the possible application of a live IBDV intermediate plus vaccine strain, the IBDV MB-1, to maternally immunized chicken embryos and day-of-hatch chicks, four large-scale field trials have been conducted in distinct global locations. The four trials have measured the relative safety, IBDV immunization parameters, and production performances of MB-1 vs. the established live and immune complex IBDV vaccines in a variety of commercial broiler systems. The overall health and production performances in all four trials have been similar or better in the MB-1 groups. The results challenge the prevailing notion that live IBDV strains may be neutralized or break through maternal immunity and induce permanent damage to the young broiler chick's immune response. A delayed replication phenomenon following parenteral administration of the live IBDV vaccine strain has been observed, while the delayed replication mechanism remains to be elucidated. This study's findings warrant further investigation of conventional live IBDV vaccine strains as an alternative for pre- and posthatch broilers active immunization.

Evaluation of Protective Efficacy When Combining Turkey Herpesvirus-Vector Vaccines.

Turkey herpesvirus (HVT) is widely used as a vaccine against Marek's disease in chickens and recently as a vector for foreign genes from infectious bursal disease virus, Newcastle disease (ND) virus, infectious laryngotracheitis (ILT) virus, and avian influenza virus. Advantages of HVT-vector vaccines are that the vaccines do not contain live respiratory viruses or live infectious bursal disease virus able to replicate and cause disease or embryo mortality, they can be administered at hatch or in ovo, and they are relatively insensitive to interference from maternally derived antibodies. As producers have tried to combine HVT-vector vaccines to protect against additional diseases, reports have indicated that applying two vectored vaccines using the same HVT vector is reported to reduce the efficacy of one or both vaccines. To confirm this interference, we evaluated commercial vaccines from multiple companies, including products with inserts designed to protect against ND, infectious ILT, and infectious bursal disease (IBD). Using a standard dosage, we found that the ILT product was most severely affected by the addition of other vaccines, as demonstrated by a significant increase in clinical signs, significant decrease in weight gain, and increase in quantity of challenge virus observed from tracheal swabs collected from Days 3-5 postchallenge. The ND and IBD products were also affected by the addition of other vaccines, although in most cases differences compared to vaccination with the vector alone were not statistically significant. This study demonstrates the importance of following manufacturer guidelines and the need for validating alternative strategies to benefit from the high level of protection offered by vector vaccines.

Comparison of growth performance and immune parameters of three commercial chicken lines used in organic production

Owing to the higher demands for avoiding medication and antibiotics, health status of the production animals plays an important role in the poultry industry, especially in organic poultry systems. Immunity plays a major role in keeping the host free from disease, and it is evident that the host’s genetic make-up influences immunity and disease resistance/susceptibility in chickens.Previously, breeding strategies aimed at selection for resistance against specific diseases with the risk of creating less disease resistance against other pathogens. Changing breeding strategies towards selection of chickens with a more general and broad disease resistance or robustness may therefore improve the overall health status, animal welfare, and food security in the poultry production. The aim of this study was therefore to compare the immunocompetence of the presumed “robust” Hellevad chickens with two chicken lines widely used in organic production, Bovans Brown (Bovans) and Hisex White (Hisex). The chickens were subjected to a routine vaccination program comprising one parasite and four viral vaccines.The current study indicates that considerable differences in immunocompetence may exist between commercial layer lines used in organic production. The Hellevad chickens were found to have higher body weight at the end of the experiment (17 weeks of age) than the other two lines. Furthermore, Hellevad and Hisex chickens were found to have higher levels of humoral innate immunity with regard to sample to positive ratio of natural antibodies in serum and concentration of mannose-binding lectin in serum as compared to Bovans. Moreover, indications of an inflammatory response were observed in the Bovans at week 5, corresponding to 1 week after vaccination with live infectious bursal disease virus. With regard to adaptive immune parameters such as IgY concentration in blood and infectious bursal disease virus (IBDV)-specific antibody titres, the Hellevad and Hisex chickens had lower levels than the Bovans. How the differences observed in growth and immune parameters in the three chicken lines influence the immune protection against infection needs to be studied further.

Modified live infectious bursal disease virus (IBDV) vaccine delays infection of neonatal broiler chickens with variant IBDV compared to turkey herpesvirus (HVT)-IBDV vectored vaccine

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.

Efficacy of HVT-IBD vector vaccine compared to attenuated live vaccine using in-ovo vaccination against a Korean very virulent IBDV in commercial broiler chickens

The production performance, efficacy, and safety of two types of vaccines for infectious bursal disease virus (IBDV) were compared with in-ovo vaccination of Cobb 500 broiler chickens for gross and microscopic examination of the bursa of Fabricius, bursa/body weight (b/B) ratio, flow cytometry, and serologic response to Newcastle disease virus (NDV) vaccination. One vaccine was a recombinant HVT-IBD vector vaccine (HVT as for herpesvirus of turkeys) and the other was an intermediate plus live IBDV vaccine. A significant difference was detected at 21 d. Eight of 10 chickens that received the IBDV live vaccine had severe bursal lesions and a relatively low b/B ratio of 0.95, and an inhibited NDV vaccine response. On the other hand, the HVT-IBD vector vaccine resulted in mild bursal lesions and a b/B ratio of 1.89. Therefore, the live vaccine had lower safety than that of the HVT-IBD vector vaccine. To determine the protective efficacy, chickens were intraocularly challenged at 24 d. Eight of 10 chickens in the IBDV live vaccination group showed gross and histological lesions characterized by hemorrhage, cyst formation, lymphocytic depletion, and a decreased b/B ratio. In contrast, the HVT-IBD vector vaccinated chickens showed mild gross and histological lesions in three of 10 chickens with a b/B ratio of 1.36, which was similar to that of the unchallenged controls. Vaccinated chickens showed a significant increase in IBDV antibody titers, regardless of the type of vaccine used. In addition, significantly better broiler flock performance was observed with the HVT-IBD vector vaccine compared to that of the live vaccine. Our results revealed that the HVT-IBD vector vaccine could be used as an alternative vaccine to increase efficacy, and to have an improved safety profile compared with the IBDV live vaccine using in-ovo vaccination against the Korean very virulent IBDV in commercial broiler chickens.

Chicken bone marrow-derived dendritic cells maturation in response to infectious bursal disease virus

Infectious bursal disease virus (IBDV) is highly contagious disease which easily lead to immunosuppression and a decreased response to vaccinations in young chicken. Since dendritic cells (DCs) are crucial to induce immunity and their maturation and functions are influenced by microbial and environmental stimuli, we investigated the effects of inactivated IBDV and IBDV on chicken DC activation and maturation. Chicken bone marrow-derived dendritic cells (chBM-DCs) cultured in complete medium (including recombinant chicken: granulocyte-macrophage colony-stimulating factor and interleukin 4) expressed high levels of MHC-II and the putative CD11c. After LPS or virus stimulation, chBM-DCs displayed the typical morphology of DCs. In addition, stimulation by LPS or viruses significantly elevated chBM-DCs surface expression levels of CD40 and CD86 molecules, as well as the ability to induce T-cell proliferative response, compared to the non-stimulated chBM-DCs. Interestingly, inactive IBDV showed stronger ability to up-regulate expression levels of CD40 and CD86 molecules and stimulate naive T cells proliferation than live IBDV. These results revealed that live viruses infection impaired DC maturation and functions, probably explaining why chickens infected with IBDV fails to trigger an effective specific immune response or develop immune memory.

Enhanced immune responses of chickens to oral vaccination against infectious bursal disease by ginseng stem-leaf saponins

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), is an immunosuppressive infectious disease of global economic importance in poultry. This study was designed to evaluate the effect of oral administration of ginseng stem-leaf saponins (GSLS) on humoral and gut mucosal immunity in chickens vaccinated with live IBDV vaccine, and furthermore, to test its protective efficacy against virulent IBDV challenge following vaccination. In experiment 1, chickens were orally administered with GSLS at 5 mg/kg of BW for 7 d, and then immunized with live IBDV vaccine via the oral route. Serum was sampled on 0, 1, 2, 3, 4, and 5 wk postvaccination for detecting antibody titers by ELISA, and intestinal tissues were collected on 0, 1, 3, and 5 wk postvaccination for measurement of IgA-positive cells and intestinal intraepithelial lymphocytes by immunohistochemical and hematoxylin-eosin staining, respectively. Result showed that antibody titers, IgA-positive cells and intestinal intraepithelial lymphocytes were significantly higher in chickens drinking GSLS than the control, suggesting an enhanced effect of GSLS on humoral and gut mucosal immune responses. In experiment 2, chickens were delivered with GSLS and then vaccinated in the same way as in experiment 1. The birds were challenged with virulent IBDV at wk 3 postvaccination. Then the birds were weighed, bled, and necropsied at d 3 postchallenge and the bursae were sampled for gross and histopathological examination. Results demonstrated that GSLS provided a better protection against virulent IBDV challenge following vaccination than the control. In conclusion, oral administration of GSLS enhances both humoral and gut mucosal immune responses to IBDV and offers a better protection against virulent IBDV challenge. Considering its immunomodulatory properties to IBDV vaccine, GSLS might be a promising oral adjuvant for vaccination against infectious diseases in poultry.

Effect of Infectious Bursal Disease Field Vaccines on Avian Influenza Vaccination Immunity

Traditional live Infectious Bursal Disease virus (IBDV) vaccines were thought to have some degree of adverse effect on bursa of fabricous of chickens, which in turn may interfere with antibodies production against other poultry vaccines. In this study, 15 broiler flocks vaccinated against avian influenza (AI) virus were sampled for serum. The flocks have received IBDV vaccination either by the conventional live vaccines or with the new recombinant subunit vaccine. Haemagglutination inhibition (HI) test were carried on sera using different AI antigens. Sera measured by the variant A/chicken/Egypt/VRLCU67/2011(H5N1) isolate showed significant difference (P

DETERMINATION OF SENSITIVITY AND SPECIFICITY OF IN-HOUSE SANDWICH ELISA FOR THE DETECTION OF INFECTIOUS BURSAL DISEASE VIRUSES

The study was designed for the development of an In-House sandwich ELISA as a suitable serological method for the rapid detection of infectious bursal disease virus (IBDV). The test was also designed to compare and evaluate its sensitivity and specificity with other traditional methods used for the detection of IBDV from field outbreak cases prevalent among the poultry population of Bangladesh. To develop the In-House sandwich ELISA, hyper-immune serum was raised against live IBDV vaccine in rabbit which was used to coat each of the 96-well flat bottomed polystyrene microtitre plate whereas, hyper-immune sera raised in chickens against IBDV used as secondary antibody. The newly developed In-House sandwich ELISA was standardized by dispensing different dilutions (10-1 up to 10-4) of rabbit serum. Among them, the 10-2 dilution of serum showed most suitable reading for the detection of IBD virus and used to coat the plate to evaluate its sensitivity and specificity. Sensitivity test was done by different dilutions (10-0 to 10-4) of reference IBD virus. The virus dilution, 10-3 was the highest dilution having lowest capacity to bind with coated antibody of the ELISA plate which indicated that IBD viruses was absent in the dilutions of above 10-3. The cut-off value of negative control samples was determined as 0.937 which indicated titer of tested samples >0.937 was positive and <0.937 was negative. Specificity test was performed using different known viruses (IBDV and NDV) using different dilutions (10-1 up to 10-4). Only the IBDV showed positive result which indicated high specificity of newly developed ELISA plate. A total of 26 samples (feces, cloacal swab, spleen and bursa) from control group, experimental and natural IBDV outbreaks were used as field viral antigen for the evaluation of sensitivity and specificity of the newly developed In-House sandwich ELISA. In case of experimental infection, 5 (62.5%) of 8 feces sample but none of cloacal swab were positive for IBDV whereas, all bursa and spleen samples were positive by both In–House sandwich ELISA and AGIDT. In case of natural outbreak cases, 6 of 6 bursal samples and 4 of 6 spleen samples were positive by In-House sandwich ELISA whereas, AGIDT detected all bursal and 3 spleen samples. No virus was detected from the samples of control group. The result showed 92.85% specificity of the developed sandwich ELISA for detection of IBDV with AGIDT which indicated that the developed ELISA is a sensitive, specific, cost effective and reliable tool for the detection of IBDV antigen from a large number of field samples.DOI = http://dx.doi.org/10.3329/bjvm.v8i2.11185 Bangl. J. Vet. Med. (2010). 8 (2) : 97-106

Genomic sequence of infectious bursal disease virus from Zambia suggests evidence for genome re-assortment in nature

Infectious bursal disease virus (IBDV) is a bi-segmented RNA virus, which belongs to the genus Avibirnavirus of the family Birnaviridae. Two serotypes, 1 and 2, exist in IBDV. The serotype 1 IBDVs are the causative agents of infectious bursal disease (IBD) in chickens worldwide and lead to immunosuppression in young birds. Genome re-assortment has been speculated to occur and contribute to the emergence of new IBDV strains. However, evidence was lacking until recently when two re-assortant viruses were detected in China. In this study, we determined the complete nucleotide sequence of an IBDV, designated KZC-104, from a confirmed natural IBD outbreak in Lusaka, Zambia in 2004. The genome consisted of 3074 and 2651 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 segment A of KZC-104 was derived from a very virulent strain, whereas its segment B was derived from a classical attenuated strain. On BLAST search, the full-length segments A and B sequences showed 98% closest nucleotide homology to the very virulent strain D6948 and 99.8% closest nucleotide homology to the classical attenuated strain D78, respectively. This is a unique IBDV reassortant strain, which has emerged in nature involving segment B of a live attenuated vaccine. This observation provides direct evidence for the involvement of vaccine strains in the emergence of reassortant IBDV in the field. Taken together, these findings suggest an additional risk of using live IBDV vaccines, which may act as genetic donors for genome re-assortment. Further studies are required to investigate the epidemiology and biological characteristics of reassortant strains so that the appropriate and safe IBDV vaccines can be recommended.

Genetic reassortment of infectious bursal disease virus in nature

Infectious bursal disease virus (IBDV), a double-stranded RNA virus, is a member of the Birnaviridae family. Four pathotypes of IBDV, attenuated, virulent, antigenic variant, and very virulent (vvIBDV), have been identified. We isolated and characterized the genomic reassortant IBDV strain ZJ2000 from severe field outbreaks in commercial flocks. Full-length genomic sequence analysis showed that ZJ2000 is a natural genetic reassortant virus with segments A and B derived from attenuated and very virulent strains of IBDV, respectively. ZJ2000 exhibited delayed replication kinetics as compared to attenuated strains. However, ZJ2000 was pathogenic to specific pathogen free (SPF) chickens and chicken embryos. Similar to a standard virulent IBDV strain, ZJ2000 caused 26.7% mortality, 100% morbidity, and severe bursal lesions at both gross and histopathological levels. Taken together, our data provide direct evidence for genetic reassortment of IBDV in nature, which may play an important role in the evolution, virulence, and host range of IBDV. Our data also suggest that VP2 is not the sole determinant of IBDV virulence, and that the RNA-dependent RNA polymerase protein, VP1, may play an important role in IBDV virulence. The discovery of reassortant viruses in nature suggests an additional risk of using live IBDV vaccines, which could act as genetic donors for genome reassortment.

Chicken recombinant antibodies against infectious bursal disease virus are able to form antibody–virus immune complex

Virus particles exposed to specific anti-virus antibodies result in the formation of immune complexes (Icx). Recent vaccination strategies have employed this feature, and an infectious bursal disease virus (IBDV) vaccine based on Icx has been released and is expected to replace conventional IBDV vaccines. We evaluated whether chicken recombinant antibodies (rAb) specific for IBDV, rather than conventional chicken anti-IBDV sera, could be used to generate Icx. Out of 14 rAb expressed as soluble single-chain variable fragments (scFv), nine were able to completely neutralize Bursavac, a live IBDV vaccine, when tested in ovo. When these rAb were mixed with IBDV and inoculated into either 18-day-old embryos, or 1-day-old or 2-week-old specific pathogen free chicks, a rAb.IBDV complex was formed. These Icx were similar to those produced by polyclonal chick anti-IBDV sera and IBDV. Following inoculation of the rAb.IBDV complex, the virus was rendered non-infectious for 5 to 7 days. After this time virus was released from the Icx, resulting in infection of the inoculated chicks and subsequent induction of an immune response and protection against virulent IBDV challenge. The results indicated that genetically derived antibodies can replace polyclonal sera in the formulation of Icx vaccines.

The enhanced virulence of very virulent infectious bursal disease virus is partly determined by its B-segment

There is a remarkable difference in virulence of infectious bursal disease virus (IBDV) strains ranging from sub-clinical infections for serotype 2 and cell culture adapted serotype 1 strains, to 100% mortality for very virulent serotype 1 strains in young SPF chickens. It is known that cell culture adaptation related attenuation is determined by distinct mutations in the hypervariable region of the VP2 outer capsid protein, encoded on the A-segment. Amino acid mutations in the hypervariable VP2 region however, offer no explanation for the difference in virulence of classical and very virulent serotype 1 strains. Here we show by in vitro and in vivo analysis of rescued segment re-asserted IBDVs that virulence factors are not only located on the A-segment, but on the RNA Dependent RNA Polymerase (VP1) encoding B-segment as well. Insight into the virulence factors of very virulent IBDV will contribute to the improvement of live IBDV vaccines.

A recombinant Newcastle disease virus (NDV) expressing VP2 protein of infectious bursal disease virus (IBDV) protects against NDV and IBDV.

Infectious bursal disease virus (IBDV) causes a highly immunosuppressive disease in chickens. Currently available, live IBDV vaccines can lead to generation of variant viruses. We have developed an alternative vaccine that will not create variant IBDV. By using the reverse genetics approach, we devised a recombinant Newcastle disease virus (NDV) vector from a commonly used vaccine strain LaSota to express the host-protective immunogen VP2 of a variant IBDV strain GLS-5. The gene encoding the VP2 protein of the IBDV was inserted into the most 3'-proximal locus of a full-length NDV cDNA for high-level expression. We successfully recovered the recombinant virus, rLaSota/VP2. The rLaSota/VP2 was genetically stable, at least up to 12 serial passages in chicken embryos, and was shown to express the VP2 protein. The VP2 protein was not incorporated into the virions of recombinant virus. Recombinant rLaSota/VP2 replicated to a titer similar to that of parental NDV strain LaSota in chicken embryos and cell cultures. To assess protective efficacy of the rLaSota/VP2, 2-day-old specific-pathogen-free chickens were vaccinated with the recombinant virus and challenged with a highly virulent NDV strain Texas GB or IBDV variant strain GLS-5 at 3 weeks postvaccination. Vaccination with rLaSota/VP2 generated antibody responses against both NDV and IBDV and provided 90% protection against NDV and IBDV. Booster immunization induced higher levels of antibody responses against both NDV and IBDV and conferred complete protection against both viruses. These results indicate that the recombinant NDV can be used as a vaccine vector for other avian pathogens.

Role of Maternal Antibodies in Protection Against Infectious Bursal Disease in Commercial Broilers

Chicks from broiler breeders with known Infectious Bursal Disease Virus (IBDV) vaccination history were examined for residual maternal and experimentally induced antibodies and their role in protectio n against IBDV. Maternal antibodies in unvaccinated chickens persisted in chicks up to 21 days as determined by ELISA with complete decay by 28 and 35 days. Experimental challenge with live IBDV protected chicks up to 14 days and resulted in 10 to 20% mortality thereafter. However, a group vaccinated with Bursine-2 and challenged with IBDV exhibited mortality in the first week post hatch and followed by complete protection until 8 weeks. These studies suggest that while maternal antibodies against IBDV persist and may protect chicks during the first 14 days of age, they may also interfere with earlier vaccine-mediated protection. Depending upon the flock IBDV antibody status, a customized vaccination regimen may be crucial for complete protection.