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PubMedDate not supplied

Embryo vaccination with infectious bursal disease virus alone or in combination with Marek's disease vaccine.

Studies with specific-pathogen-free chickens revealed that chicks hatching from eggs inoculated at the 18th day of embryonation with infectious bursal disease (IBD) vaccine viruses of low virulence (isolates TC-IBDV and BVM-IBDV) developed antibody against IBD virus (IBDV) and resisted challenge with virulent IBDV at 3 weeks of age or older. Embryo vaccination did not adversely affect hatchability of chicks or survival of hatched chicks. Chicks embryonally vaccinated with TC-IBDV had transient histologic lesions in the bursa of Fabricius at hatch. Similar but milder lesions were also noted in chickens that received TC-IBDV at hatch. The level of protection following embryo vaccination with TC-IBDV and BVM-IBDV was similar to that following vaccination with the same vaccines at hatch. Vaccine viruses of moderate virulence (isolates BV-IBDV and 2512-IBDV) were not suitable as vaccines in embryos lacking maternal antibody to IBDV, because the vaccinated chicks developed acute IBD after hatch. Isolate 2512-IBDV was not pathogenic for embryos bearing maternal antibody to IBDV. Maternal antibody against IBDV interfered with efficacy of embryo vaccination with BVM-IBDV but not with 2512-IBDV. Embryo vaccination with a mixture of vaccines against IBD and Marek's disease resulted in protection of hatched chicks against challenge with virulent IBDV and Marek's disease virus.

Animals↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

Detection of infectious bursal disease vaccine viruses in lymphoid tissues after in ovo vaccination of specific-pathogen-free embryos.

Control of infectious bursal disease virus (IBDV) by vaccination is important for poultry production worldwide. Two vaccines, an IBDV immune complex (ICX) vaccine and an IBDV-2512 vaccine, were administered at 100 mean embryo infectious dose to specific-pathogen-free 18-day-old broiler embryos in ovo. At 3, 6, 9, 15, and 21 days post in ovo vaccination (PIOV), bursa, spleen, and thymus tissues were collected and analyzed for virus protein by antigen capture chemiluminescent enzyme-linked immunosorbent assay (ELISA). Chicks were bled and antibody titers were determined by the antibody ELISA. At 21 days PIOV, chickens were challenged with a 1:500 dilution of an antigenic standard IBDV strain. At 28 days PIOV, birds were euthanatized and bursa weight:body weight ratios were determined. Embryos vaccinated with either vaccine exhibited 92% hatchability; however, within 1 wk of hatch, birds vaccinated with IBDV-2512 showed 56% mortality, whereas those given IBDV-ICX had only 3.2% mortality. Both IBDV-ICX and IBDV-2512 vaccines were detected in bursa, spleen, and thymus at day 3 PIOV. A 5-day delay in virus replication was observed with IBDV-ICX vaccine. By day 15 PIOV, the IBDV-ICX was no longer detectable in the bursa and spleen but persisted in the thymus. The IBDV-2512 vaccine persisted in the spleen and thymus on day 15 PIOV. By day 21 PIOV, neither vaccine virus was detected in any lymphoid organ. This assay can be useful in the early detection of vaccine virus in the tissues of chickens vaccinated via the in ovo route. Both vaccines caused bursal atrophy at all times PIOV. The IBDV-2512 caused splenomegaly at day 6 PIOV, whereas splenomegaly was not seen in IBDV-ICX-vaccinated birds until day 9 PIOV. Thymus atrophy was observed in IBDV-2512-vaccinated chicks from day 3 PIOV, whereas this occurred on day 15 PIOV in IBDV-ICX-vaccinated birds. Bursa weight: body weight ratios in IBDV-ICX-vaccinated unchallenged and vaccinated challenged birds were not different (P < 0.05).

Animals↗

PubMed1990

Nucleotide sequence analysis of genome segment A of infectious bursal disease virus.

The nucleotide sequence of genome segment A cDNA of the STC strain of infectious bursal disease virus (IBDV) was determined and compared with sequences of the homologous genome segment of the 002-73 strain of IBDV and the Jasper strain of infectious pancreatic necrosis virus (IPNV). The STC-IBDV genome segment A was determined to be 3262 base pairs (bp), which is close to the estimated total length of 3300 bp for genome segment A in IBDV, although there is no proof that it is the real length of this genome segment. The STC-IBDV genome segment A contains two major overlapping open reading frames (ORFs). The large ORF of 3036 bp predicts a polyprotein of Mr 109,358, whereas the small ORF is 435 bp and predicts a protein of Mr 16,550 in STC-IBDV. STC-IBDV and 002-73-IBDV polyproteins are closely related (97.4% amino acid homology). Most of the amino acid mismatches are in VP2 sequences, mainly within the area of the conformation-dependent epitope. Comparison with the Jasper-IPNV polyprotein reveals levels of amino acid sequence homology of about 40% in VP2, 32% in VP3 and 21% in VP4. Within the VP2 molecule the conformation-dependent epitope area is again the least homologous, but the heterogeneity is more conspicuous than between the two IBDV strains, which is not surprising since IBDV and IPNV are serologically unrelated. The small ORF proteins have about 88% amino acid sequence homology between STC-IBDV and 002-73-IBDV, and 30% between each IBDV strain and Jasper-IPNV. There is no homology at all in the non-coding regions of IBDV and IPNV. These comparative sequence data will be useful for subgrouping the Birnaviridae family.

Amino Acid Sequence↗

PubMedDate not supplied

Evaluation of the immune response and detection of infectious bursal disease viruses by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay after in ovo vaccination of commercial broilers.

Maternal immunity can interfere with infectious bursal disease virus (IBDV) vaccine efficacy. The effect of maternal antibody (MacAb) on the immune response and detection of two vaccine viruses, an IBDV immune complex (cx) and IBDV-2512, was investigated. Vaccines were administered in ovo at 100 mean embryo infectious dose to commerical broiler embryos derived from young (29 wk) or old (63 wk) flocks. Chickens with low MatAb were challenged with an antigenic standard IBDV strain at 21 and 35 days post in ovo vaccination (PIOV). At 28 and 42 days PIOV, birds were euthanatized and bursa weight: body weight ratios were determined. MatAb of progeny from the 29-wk-old flock was higher (P < 0.05) than that from progeny of the 63-wk-old flock. Progeny titers declined by day 21 PIOV. Birds with MatAb vaccinated with either the IBDV-2512 or IBDV-Icx vaccine did not mount an antibody response by 21 days PIOV. The IBDV-Icx vaccination protected chickens against bursal atrophy when they were challenged at 21 and 35 days PIOV (83% and 77%, respectively). Resistance to challenge in the absence of antibody implies that cellular immunity plays a role in IBDV protection. The IBDV-2512 vaccine caused atrophy of the bursae, and, therefore, we could not examine its protection by these criteria. Neither vaccine could be detected by antigen-capture chemiluminescent enzyme-linked immunosorbent assay. Therefore, total RNA was extracted and reverse transcription (RT)-polymerase chain reaction (PCR) and nested PCR were conducted to amplify the VP2 (hypervariable) region on viral RNA collected at 3, 6, 9, 15, and 21 days PIOV. Nested PCR detected the VP2 region of both IBDV vaccine viruses at day 3 PIOV. Only IBDV-2512 RNA was detected on day 6 PIOV. However, the IBDV-Icx RNA was detected on days 9 and 15 PIOV but not on day 21 PIOV. The IBDV-Icx RNA was evident in tissues and could induce protection against challenge. This work gives further insight into the mechanism of the IBDV-Icx vaccine.

Animals↗

PubMed2002

Confirmation of the existence of two distinct genetic groups of infectious bursal disease virus in Australia.

OBJECTIVE: To characterise infectious bursal disease viruses (IBDVs) prevalent at major commercial sites throughout Australia and to compare the nucleic acid sequences of local strains of IBDV with those of characterised overseas strains. DESIGN: Samples of bursae were collected from 20 broiler farms that belonged to different poultry companies in New South Wales (NSW), Queensland (Qld), Victoria (Vic), Westem (WA) and South Australia (SA). METHOD: Bursae were collected from broilers between 24 and 35 days of age. Bursal tissue was homogenised and tested for the presence of IBDV antigen using four monoclonal antibodies (Mabs) which detect antigenic variation in IBDV strains. The nucleotide sequences of the hypervariable region (HVR) within the VP2 gene of IBDVs was determined and the deduced amino acid sequences compared with three vaccine strains and six previously characterised Australian IBDV strains. The deduced amino acid sequences were also compared with the published amino acid sequences of overseas strains. The phylogenetic relationships between Australian strains and overseas strains were then determined. RESULTS: IBDV was detected in birds from 14 out of 20 farms sampled. Typing with four Mabs showed that all viruses from Vic (6) and SA (10) were antigenic variants, whereas all viruses from NSW (29), Qld (4) and WA (5) were classical-like strains. Nucleotide sequencing of one sample from each of the 14 farms on which IBDV was detected confirmed results obtained with Mabs. The amino acid sequences of all Australian viruses differed from the amino acid sequences of foreign IBDV strains. Phylogenetic analysis showed that Australian IBDV viruses belonged to two distinct genetic groups. Very virulent (vv) IBDV strains belonged to a third genetic group, and overseas classical and variant strains belonged to a fourth genetic group. CONCLUSIONS: The results confirmed previous findings that there are two groups of IBDV strains circulating in commercial broilers in Australia. The majority are classical-like strains that are antigenically and genetically similar to vaccine strains 002/73 and V877. These classical strains were prevalent in broilers in three states, NSW, Qld and WA. The second group of strains are antigenic variants that were only found in broilers in two states, Vic and SA. All Australian IBDVs characterised to date are genetically distinct and can be differentiated from all other overseas strains. This enables identification of incursion of any exotic strain into Australian poultry, be it classical, US variant or wIBDV strains.

Amino Acid Sequence↗

PubMedDate not supplied

Detection of infectious bursal disease viruses in commercially reared chickens using the reverse transcriptase/polymerase chain reaction-restriction endonuclease assay.

Bursa samples from the United States, Mexico, and Puerto Rico were tested for the presence of infectious bursal disease virus (IBDV) using the reverse transcriptase/polymerase chain reaction-restriction endonuclease (RT/PCR-RE) assay. This assay amplifies a 394-bp fragment of the IBDV VP2 gene. A total of 151 samples were tested. Each was from a different physical location or farm. Forty-eight of the samples were determined to contain IBDV using RT/PCR. The RE profiles on 44 of these positive samples were determined using the enzymes BstNI or EcoRII, StyI, DraI, SacI, Sau3AI or MboI, and TaqI. A majority of the samples (34) had RE profiles typical of variant IBDV strains. One of six samples from Mexico was positive for IBDV. This virus had an RE profile typical of variant strains of IBDV. Three of seven samples from Puerto Rico had RE profiles characteristic of variant viruses. Two samples from the United States had RE profiles characteristic of classic vaccine IBDV strains and nine samples had new RE profiles. Five of these new profiles were BstNI- and StyI-negative, indicating that these viruses may be antigenically related to variant types. Although the new RE pattern observed in the other four samples was BstNI- and StyI-positive, it was not typical of classic vaccine IBDV strains. One flock from the United States had a mixture of two RE profiles, a typical variant type profile and an unknown variant RE profile. Two-thirds of the positive samples from flocks where the age of the birds was reported were observed between 21 and 28 days of age. The results of these studies demonstrate that the RT/PCR-RE assay can be used to diagnose IBDV in chickens and that IBDV strains exist in commercially reared chickens that have RE patterns different than known IBDV strains. The molecular differences observed using the RT/PCR-RE test were in a region of the VP2 gene, which is known to code for important neutralizing epitopes and to be highly variable among IBDV strains. Although the results demonstrate RE patterns different than those observed in known classic and variant IBDV strains, the influence of these molecular differences on biological properties of the viruses requires further investigation.

Aging↗

PubMed1998

The working mechanism of an immune complex vaccine that protects chickens against infectious bursal disease.

The role of immune complexes (Icx) in B-cell memory formation and affinity maturation allow for their potential use as vaccines. Recently, a new immune complex vaccine has been developed that is currently under field trials conducted in commercial poultry. This immune complex vaccine is developed by mixing live intermediate plus infectious bursal disease virus (IBDV) with hyperimmune IBDV chicken serum (IBDV-Icx vaccine). Here we have investigated the infectivity of this vaccine as well as the native IBDV (uncomplexed) vaccine in terms of differences in target organs, in target cells and speed of virus replication. At various days after inoculation on day 18 of incubation (in ovo) with either one dose of virus alone or the IBDV-Icx vaccine, the replication of IBDV and the frequency of B cells and other leucocyte populations were examined in the bursa of Fabricius, spleen, and thymus using immunocytochemistry. With both vaccines, IBDV was detected associated with B cells, macrophages and follicular dendritic cells (FDC) in bursa and spleen, although complexing IBDV with specific antibodies caused a delay in virus detection of about 5 days. Most remarkable was the low level of depletion of bursal and splenic B cells in IBDV-Icx vaccinated chickens. Furthermore, in ovo inoculation with the IBDV-Icx vaccine induced more germinal centres in the spleen and larger amounts of IBDV were localized on both splenic and bursal FDC. From these results we hypothesize that the working mechanism of the IBDV-Icx vaccine is related to its specific cellular interaction with FDC in spleen and bursa.

Animals↗

PubMedDate not supplied

Effect of a variant infectious bursal disease virus (E/Del) on Salmonella typhimurium infection in commercial broiler chickens.

The effect of infectious bursal disease virus (IBDV) on Salmonella typhimurium (ST) infections in broilers was investigated in terms of Salmonella shedding and persistence, pathogenicity, and isotype specific humoral immune responses. Thirty-six, 1-day-old, straight-run commercial broiler chickens that were Salmonella negative by polymerase chain reaction (PCR) and culture were divided into two groups of 18 chicks each (ST and ST-IBDV). One group (ST-IBDV) of chicks received the E/Del strain of IBDV (10(5.0) median tissue culture infective dose [TCID50]/ml) through the ocular and cloacal routes divided into doses of 50 microl each at 2 days of age. Both groups were then inoculated with 10(8) colony-forming units (CFU)/ml nalidixic acid-resistant ST in the drinking water at 3 days of age. Environmental Salmonella counts were higher in the ST-IBDV group at 2 and 3 wk postinfection (PI) compared to the ST group. ST carriage in the cecal contents between the ST and ST-IBDV groups was not statistically different. The ST-IBDV group had a single mortality at 10 days postinfection compared to none in the ST group. The ST-IBDV group had significantly lower bursa to body weight ratios at 4 and 6 wk, as well as higher bursal lesion scores than the ST group at 2, 4, and 6 wk PI. The ST group had significant increase in serum IgG from 2 to 6 wk PI in comparison to the ST-IBDV group, which had no significant changes over time. Both IgA and IgM were significantly increased at 4 and 6 wk relative to 2-wk levels. There was an IBDV-induced failure of anti-Salmonella IgG seroconversion over time in ST-IBDV. Both groups continued to shed high levels of Salmonella up to the end of the study despite high antibody levels in the ST group and an unimpaired IgM and IgA production in the ST-IBDV group, indicating a limited influence of humoral immunity on Salmonella clearance.

Animals↗

PubMedDate not supplied

A highly sensitive, broad-spectrum infectivity assay for infectious bursal disease virus.

In order to develop an infectivity assay for infectious bursal disease virus (IBDV), an enzyme-linked immunosorbent assay (ELISA) for detecting IBDV antigens was developed using a rabbit antiserum to IBDV. The ELISA detected both serotypes 1 and 2 of IBDV, purified virus proteins at a concentration of about 0.1 ng/well and about 10(4) to 10(5) infectious units/well, and was about 10(3) times more sensitive than an agar gel precipitin test. By using the ELISA for detecting IBDV antigens in the cultured fluids, infectivity titration could be determined within 5 days of cultivation in seven of the 10 virus-cell combinations when chicken embryo fibroblasts (CEFs), BGM-70 cells, and LSCC-BK3 cells were used. IBDV antigens were not detected in three combinations remaining after 7 days of cultivation. When 18 IBDV strains, including highly virulent, classically virulent, and attenuated strains, were tested for growth in four types of cells using the ELISA, eight strains in CEFs, seven strains in chicken kidney cells, five strains in BGM-70 cells, and 17 strains in LSCC-BK3 cells were detected. These results indicated that LSCC-BK3 cells had the broadest spectrum for IBDV. When 26 field bursal homogenates were tested for infectious IBDV using LSCC-BK3 cells, all 19 field IBDV isolates that were detected by immunostaining of the cells were also detected by the ELISA. These results indicate that this infectivity assay for IBDV using LSCC-BK3 cells and the ELISA has a high sensitivity and a broad spectrum for IBDV and is especially useful for large-scale applications.

Birnaviridae Infections↗

PubMed1993

Infectious bursal disease virus structural proteins expressed in a baculovirus recombinant confer protection in chickens.

Plasmids were prepared that contained cDNA segments of the large genomic segment A of infectious bursal disease virus (IBDV) strain GLS-5. The genes encoding the IBDV structural proteins (VP2, VP3 and VP4) were introduced into the baculovirus transfer vector pBlueBacI to obtain a recombinant baculovirus vIBD-7. When insect cells were infected with recombinant viruses, the result was synthesis of IBDV precursor proteins which were processed by the viral protease. The recombinant IBDV antigens were characterized by immunoprecipitation with monoclonal antibodies (MAbs) and polyclonal antiserum to IBDV, and by antigen-capture ELISA using a panel of IBDV-specific MAbs. The recombinant IBDV antigens closely resembled the native IBDV proteins and reacted with all the GLS-5 strain-specific neutralizing MAbs that recognize only conformational epitopes of IBDV. When susceptible chickens were inoculated with the recombinant IBDV antigens, virus-neutralizing antibodies were induced that conferred up to 79% protection against IBDV challenge.

Animals↗

PubMedDate not supplied

Infectious bursal disease virus and proventriculitis in broiler chickens.

Acute necrotic proventriculitis is a naturally occurring disease of broiler chickens that causes proventricular rupture during routine evisceration. Although infectious bursal disease virus (IBDV) has been implicated, it has not been proven to be a direct cause of this disease. To further study the role of IBDV in proventriculitis, proventriculi and bursas were collected during both acute and chronic phases of naturally occurring proventriculitis and from chickens experimentally infected with seven different [BDV strains. All tissues were examined for IBDV by light microscopy, immunohistochemistry (IHC), and real time reverse transcriptase(RT)-polymerase chain reaction (PCR) and for apoptosis by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling method (TUNEL). Tissues from naturally occurring proventriculitis had bursal and proventricular lesions. Two out of four bursas had no IHC-stainable IBDV antigen or RT-PCR detectable IBDV sequences. No proventriculus had IBDV detectable by any of these methods. Bursas from chickens experimentally infected with IBDV had microscopically evident lesions, IBDV was detectable by IHC and RT-PCR, and strong IHC staining for apoptosis was present. Proventriculi from these experimentally exposed chickens had no lesions, low levels of IBDV detectable by IHC or RT-PCR, and very little IHC-stainable apoptosis. We conclude that naturally occurring proventriculitis can occur in the absence of IBDV and that the IBDV strains tested do not directly produce proventriculitis or induce increased proventricular apoptosis.

Animals↗

PubMedDate not supplied

Effect of infectious bursal disease virus on protection against Marek's disease by turkey herpesvirus vaccine.

Chickens inoculated at hatch with pathogenic infectious bursal disease virus (IBDV) and the turkey herpesvirus (HVT) vaccine were poorly protected against challenge at 1 week with virulent Marek's disease virus (MDV). However, if vaccination with HVT preceded IBDV inoculation such as by embryonal vaccination with HVT and exposure to IBDV at hatch, or by vaccination at hatch and IBDV exposure 5 days or longer postvaccination, then the vaccinal efficacy of HVT was not influenced. Further, the inhibitory effect of pathogenic IBDV was transient: chickens that received IBDV and HVT at hatch were poorly protected against challenge with virulent MDV at 1 week but not against challenge at 2 weeks of age. Pathogenic IBDV routinely interfered in vaccine efficacy of HVT in chickens lacking maternal antibody to IBDV but not in chickens that had such antibodies at the time of exposure to IBDV. In certain experiments, pathogenic IBDV caused a high rate of mortality in newly hatched chicks. Chickens receiving IBDV and MDV had a lower incidence of Marek's disease than those receiving MDV alone.

Animals↗

PubMed1998

Infectious bursal disease virus changes the potassium current properties of chicken embryo fibroblasts.

Infectious bursal disease virus (IBDV) is the causative agent of an economically significant poultry disease. IBDV infection leads to apoptosis in chicken embryos and cell cultures. Since changes in cellular ion fluxes during apoptosis have been reported, we investigated the membrane ion currents of chicken embryo fibroblasts (CEFs) inoculated with the Cu-1 strain of IBDV using the patch-clamp recording technique. Incubation of CEFs with IBDV led to marked changes in their K+ outward current properties, with respect to both the kinetics of activation and inactivation and the Ca2+ dependence of the activation. The changes occurred in a time-dependent manner and were complete after 8 h. UV-treated noninfectious virions induced the same K+ current changes as live IBDV. When CEFs were inoculated with IBDV after pretreatment with a neutralizing antibody, about 30% of the cells showed a normal K+ current, whereas the rest exhibited K+ current properties identical to or closely resembling those of IBDV-infected cells. Incubation of CEFs with culture supernatant from IBDV-infected cells from which the virus particles were removed had no influence on the K+ current. Our data strongly suggest that the K+ current changes induced by IBDV are not due to virus replication, but are the result of attachment and/or membrane penetration. Possibly, the altered K+ current may delay the apoptotic process in CEFs after IBDV infection.

Animals↗

PubMed2006

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.

Amino Acid Substitution↗

PubMed2003

DNA vaccination with plasmids containing various fragments of large segment genome of infectious bursal disease virus.

The present study was undertaken to determine the effectiveness in including VP2 gene of the large segment genome of infectious bursal disease virus (IBDV) in the DNA vaccine for protection of chickens against infectious bursal disease (IBD). Different fragments of the large segment gene of IBDV standard challenge (STC) strain were successfully amplified by reverse transcription-polymerase chain reaction (RT-PCR) followed by cloning into a eukaryotic expression plasmid vector (pCR3.1) as DNA vaccines. Transient expression of the encoded genes from various constructed plasmids was characterized in COS-7 cells by positive immunofluorescent staining with polyclonal or monoclonal antibody to IBDV. Chickens (1-day old) were intramuscularly injected with the individual plasmid three times at weekly intervals, challenged with IBDV strain STC at 21-day old, and observed for 10 days. Chickens receiving the plasmids containing VP2 genes, including VP243, VP24, or VP2 fragment, did not have clinical signs, mortality, and bursal atrophy and were effectively protected against IBDV infection. On the contrary, chickens receiving plasmids without containing VP2 genes, including VP4, VP3, or VP43 fragment, had marked bursal atrophy and were not protected against IBD. Antigen detection was correlated with protection; chickens protected from IBDV infection had undetectable IBDV antigen in bursae. Enzyme-linked immunosorbent assay (ELISA) antibody titer to IBDV was low or undetectable prior to or after challenge with IBDV in protected chickens receiving the plasmids containing the VP2 gene. The results indicate that inclusion of VP2 gene in the plasmid DNA is essential in achieving effective protection mediated by DNA vaccination against IBDV infection in chickens.

Animals↗

PubMed2004

Virus strains from a flock exhibiting unusually high mortality due to infectious bursal disease.

OBJECTIVE: To characterise infectious bursal disease viruses (IBDVs) isolated from commercial broiler flocks exhibiting unusually high mortality due to infectious bursal disease (IBD). DESIGN: An IBD outbreak occurred in mid 1999 on two broilers farms (A and B) in northern New South Wales amongst chickens 28 to 38 days of age, with a sharp rise in mortality of 2.5%. Initial histopathological diagnosis indicated acute IBD. Since acute IBD caused by classical pathogenic and very virulent (vv) IBDVs is exotic to Australia, samples from both farms A and B were obtained and used for virus characterisation. METHOD: Tissue homogenates were made from six bursae collected from farm B. One histological sample from farm A was also used. Nucleotide sequencing of the hypervariable region (HVR) within the VP2 gene of IBDVs was determined and the deduced amino acid sequences compared with previously characterised Australian and overseas IBDVs. The phylogenetic relationship between IBDVs from farm B and IBDVs from Australia and overseas was then determined. Pathogenicity of one isolate, N2/99 from farm B, was compared with 3 other local IBDVs, as well as with three pathogenic overseas strains in 3-week-old specific pathogen-free (SPF) chickens. RESULTS: Initial histopathological characterisation of a sample of bursa from a bird on farm A showed widespread acute lymphoid necrosis, follicular haemorrhage and stromal oedema, indicative of acute IBD. Subsequent analysis using reverse transcriptase polymerase chain reaction (RT-PCR), followed by nucleotide sequencing of the same bursal sample, as well as 6 samples from nearby farm B, showed that the IBDVs involved were similar in sequence to Australian vaccine strains and not to classical pathogenic or vvIBDVs. One isolate, N2/99 from farm B, was only marginally more pathogenic than other local IBDVs. It induced mild clinical signs in 30% of chicks and no mortality. In comparison, vvIBDV CS89 and classical pathogenic 52/70 strains induced severe clinical signs in 100% and 80% of chickens, respectively with mortalities of 27% and 12%, respectively. CONCLUSIONS: The results illustrated the value of nucleotide sequencing as a method for discrimination of local and exotic types of IBDV.

Amino Acid Sequence↗

PubMed1999

Efficient rescue of infectious bursal disease virus from cloned cDNA: evidence for involvement of the 3'-terminal sequence in genome replication.

To study the mechanism of replication of infectious bursal disease virus (IBDV), and to determine factors on the IBDV RNA which are involved in viral replication, we used cloned full-length cDNA of both the A- and B-segments to generate infectious IBDV. Infectious IBDV was rescued from plasmids that contained full-length IBDV cDNA behind a T7 promoter, by transfecting these plasmids into cells which were infected with a recombinant Fowlpox virus that expressed T7 RNA polymerase. By using the cDNA transfection system we evaluated the effect of the length of the 3' terminus of the A-segment plus strand of IBDV. Although wild-type IBDV predominantly contains four cytosines at the 3' terminus, no difference in virus yield was found when virus was rescued from cDNAs containing three to six adjacent cytosines. When the 3' terminus was shorter than three cytosines the efficiency to generate infectious IBDV from cDNA was reduced, but IBDV could still be recovered reproducibly. The rescued viruses from cDNAs containing 3'-terminal deletions appeared to have a restored 3'-terminal sequence. The missing nucleotides are probably restored by using complementary bases of a stem-loop structure as template.

Animals↗