Live Infectious Bursal Disease Virus Vaccine 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.

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.

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.

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.

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.

Complete, Long-Lasting Protection against Lethal Infectious Bursal Disease Virus Challenge by a Single Vaccination with an Avian Herpesvirus Vector Expressing VP2 Antigens

Marek's disease herpesvirus is a vaccine vector of great promise for chickens; however, complete protection against foreign infectious diseases has not been achieved. In this study, two herpesvirus of turkey recombinants (rHVTs) expressing large amounts of infectious bursal disease virus (IBDV) VP2 antigen under the control of a human cytomegalovirus (CMV) promoter or CMV/beta-actin chimera promoter (Pec promoter) (rHVT-cmvVP2 and rHVT-pecVP2) were constructed. rHVT-pecVP2, which expressed the VP2 antigen approximately four times more than did rHVT-cmvVP2 in vitro, induced complete protection against a lethal IBDV challenge in chickens, whereas rHVT-cmvVP2 induced 58% protection. All of the chickens vaccinated with rHVT-pecVP2 had a protective level of antibodies to the VP2 antigen at the time of challenge, whereas only 42 and 67% of chickens vaccinated with rHVT-cmvVP2 or the conventional live IBDV vaccine, respectively, had the antibodies. The antibody level of chickens vaccinated with rHVT-pecVP2 increased for 16 weeks, and the peak antibody level persisted throughout the experiment. The serum antibody titer at 30 weeks of age was about 20 or 65 times higher than that of chickens vaccinated with rHVT-cmvVP2 or the conventional live vaccine, respectively. rHVT-pecVP2, isolated consistently for 30 weeks from the vaccinated chickens, expressed the VP2 antigen after cultivation, and neither nucleotide mutations nor deletion in the VP2 gene was found. These results demonstrate that the amount of VP2 antigen expressed in the HVT vector was correlated with the vaccine efficacy against lethal IBDV challenge, and complete protective immunity that is likely to persist for the life of the chickens was induced.

Rescue of infectious bursal disease virus from mosaic full-length clones composed of serotype I and II cDNA

Infectious Bursal Disease Virus (IBDV) is the causative agent of one of the most important and wide-spread infectious diseases among commercial chicken flocks. IBDV causes a depletion of B-lymphoid cells in the bursa of Fabricius, inducing immunosuppression, morbidity, or even acute mortality. Because currently used live IBDV vaccines are derivatives from field isolates no serologic discrimination between field isolates and live vaccines can be made. The recently developed reverse genetics techniques for IBDV allows one to generate genetically modified IBDVs which might have altered biological and antigenic properties. Here, we describe the rescue of mosaic serotype I IBDVs, of which the polyprotein encoding region was partly replaced by the corresponding region of a serotype II strain. A mosaic virus, containing the C-terminal part of serotype II VP3 showed only a slightly delayed release of progeny virus compared to unmodified serotype I virus, while maximum viral titers at 25 h post infection were equal. Since serotype specific epitope(s) are present in the C-terminal part of VP3, we were able to discriminate this rescued virus from serotype I and II IBDV strains. These findings make the use of a chimeric VP3 a promising approach to develop an IBDV marker vaccine.

Detection and Persistence of Infectious Bursal Disease Virus in Specific-Pathogen-Free and Commercial Broiler Chickens

In an earlier study, specific-pathogen-free (SPF) chickens were inoculated with infectious bursal disease virus (IBDV) at 3 wk of age. Their bursas were examined for virus at different intervals postinoculation (PI) by reverse transcriptase (RT)/polymerase chain reaction (PCR) and by virus isolation in chicken embryos up to 21 days PI. The RT/PCR was positive, but attempts to isolate infectious virus from bursal homogenates failed. This prompted us to investigate the persistence of IBDV or its RNA in the bursa of Fabricius (BF) of inoculated and vaccinated SPF chicks and of inoculated and vaccinated commercial broiler chicks that have maternally derived antibodies. Four trials were conducted in SPF and commercial broiler chickens. Infectious virus was detected by embryo inoculation up to 7 days PI in the BF of SPF chickens inoculated at 2 or 3 wk of age and up to 21 days PI by RT/PCR, whereas the viral RNA was detected by RT/PCR for up to 28 days PI. In SPF chicks inoculated at 1 day of age, the bursa-derived virus or its RNA was detected at 7 and 14 days PI when inoculated at a high dose (10(4) mean embryo infective dose [EID50]/bird) or at a low dose (10(2.5) EID50/bird). In commercial 1-day-old broiler chicks, the bursa-derived virus was detected at 7 and 14 days PI when inoculated at a high dose (10(4) EID50/bird), whereas the virus was detected only at 14 days PI when inoculated at a low dose (10(2.5) EID50/bird). In SPF and commercial chicks vaccinated with a modified live IBDV vaccine, the virus or its RNA was detected at 7 and 14 days postvaccination in SPF chicks, but neither the live vaccine virus nor its RNA was detected in commercial broilers vaccinated at 1 day or 2 wk of age.

Safety and Efficacy of in ovo Administration of Infectious Bursal Disease Viral Vaccines

In ovo vaccination against Marek's disease virus and infectious bursal disease virus (IBDV) in commercial broilers in the United States is common. Little information exists as to the safety and efficacy of intermediate IBDV vaccines given in ovo. Experiments were initiated to determine the safety and efficacy of three commercially available live intermediate IBDV vaccines by in ovo route. Commonly used vaccines were given at 18 days of embryonation to specific-pathogen-free (SPF) broiler embryos (first and second study) or to commercial broiler embryos (third study) that had maternal antibody against IBDV. When any of the antigenic standard vaccines was given at full dose to SPF embryos, embryonic and 3-wk posthatch mortality increased. Vaccines also caused significant microscopic lesions in the bursa of Fabricius at 1 and 3 wk posthatch. In contrast, there was no adverse effect on embryonic or posthatch mortality when vaccines were given at half dose to SPF or commercial broiler embryos. However, significant microscopic lesions were evident at 1 and 3 wk posthatch in the bursae of SPF embryos given the vaccines at half dose. When vaccines were given at half dose to commercial broiler embryos, lesions were evident at 1 but not 3 wk of age. In the third study, in ovo vaccinated chickens were challenged with either a virulent standard (APHIS) or antigenic variant (variant E) IBDV virus at 3 wk of age. All vaccines produced at least 87% protection against the standard and 60% protection against the variant challenge IBDV, as measured by bursal weight to body weight ratios. This study was the first to examine the safety and efficacy of the three commonly used intermediate IBDV vaccines given in ovo in protection against standard and antigenic variant IBDV challenge viruses.

Efficacy of a Novel Infectious Bursal Disease Virus Immune Complex Vaccine in Broiler Chickens

Two experiments were conducted to test the efficacy of a novel infectious bursal disease virus (IBDV) vaccine in broiler chickens with maternal IBDV immunity. The IBDV vaccine was formulated by mixing IBDV strain 2512 with bursal disease antibodies (BDA) to produce the IBDV-BDA complex vaccine. In Expt. I, 1-day-old Cobb x Cobb broiler chickens were vaccinated subcutaneously with either IBDV-BDA or commercial live intermediate IBDV vaccine (vaccine A) or were left unvaccinated. In Expt. 2, the vaccine A group was not included; instead, IBDV strain 2512 was included. Chickens were maintained in isolation houses. On day 28 (Expt. 1) and day 32 (Expt. 2) of age, chickens from each group were challenged with a standard USDA IBDV (STC strain) challenge. Challenged and unchallenged chickens were evaluated for their bursa/body weight ratios and antibody titers 3 days post-challenge. Bursae collected from Expt. 2 were examined histologically to evaluate bursal lesions and confirm gross examination. None of the unvaccinated chickens was protected against the challenge virus as evidenced by the presence of acute bursal lesions (edema/hemorrhage). All chickens receiving the IBDV-BDA complex or the IBDV strain 2512 (Expt. 2) were protected from the challenge virus as evidenced by no acute bursal lesions. Additionally, chickens receiving the IBDV-BDA complex vaccine or the IBDV strain 2512 had antibody titers to IBDV, indication the presence of an active immune response. In Expt. 1, chickens vaccinated with vaccine A and challenged had bursal lesions similar to those observed in the unvaccinated, challenged chickens. These chickens also showed no indication of active immunity against the virus. These results suggest that the 1-day-of-age-administered IBDV-BDA complex vaccine can induce active immunity and protection against a standard IBDV challenge in the face of variable levels of maternal IBDV immunity.

Interaction of aflatoxin in the feed and immunization against selected infectious diseases. I. Infectious bursal disease

Summary A study was conducted on the impact of aflatoxin in the feed on immunization against infectious bursal disease (IBD) in chickens using an attenuated live vaccine. Three‐hundred‐and‐ninety broiler chicks were used. The aflatoxin feeding of 100 and 200 parts/109 of AFBI started when chicks were 10 days old and continued for 8 weeks. An attenuated live IBD virus vaccine was administered in drinking water at 2 and 5 weeks of age. A field IBD virus strain was used for challenge. The antibody titres, bursal indices, bursal lymphocyte counts and feed conversion ratios were monitored. The impact of aflatoxin on reduced body weights and lower antibody titres was shown to be highly significant (P<0.0001).

Response of B Congenic Chickens to Infection with Infectious Bursal Disease Virus

Six congenic lines of chickens that differ from the parental inbred line RPRL-15I5 for genes in the major histocompatibility (B) complex were used to study the influence of the B haplotypes on the response of chickens to infection with virulent infectious bursal disease virus (IBDV) at 1 day or 4 weeks of age, and on the antibody response to vaccination with live or inactivated oil-emulsion (OE) IBDV vaccines at 7 weeks of age. IBDV-induced immunodepression and lesions in the bursa, spleen, and thymus in chickens infected with virus at 1 day of age were of the same degree of severity, regardless of line of chickens used. The response of blood cells to the mitogens phytohemagglutinin-M and concanavalin A was elevated in chickens infected with IBDV at 1 day of age. In an experiment conducted to study the effect of the B haplotype on IBDV infection in 4-week-old chickens, B congenic line C-12 (B12B12) showed the highest susceptibility to clinical IBD, with mortality of 79%. No detectable difference in the serological response to vaccination with live or OE IBDV vaccines was noted among chickens of various congenic lines. We conclude that the B haplotypes may influence IBDV-induced mortality, but not immunodepression or severity of lesions in lymphoid organs, or the antibody response to live or OE IBDV vaccines.