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Prevention of infectious bursal disease (IBD) by feeding IBD virus-immune bovine colostrum.

Addition of 5% freeze-dried IBD virus (IBDV)-immune bovine colostrum to the diet of chickens prevented infection when housed in an IBDV-contaminated environment. Four of five chickens receiving 2.5%, and all chickens receiving 0.5% or no IBDV-immune colostrum were infected. No interference with development of an active immunity was found in chickens receiving 5% IBDV-immune colostrum in their diet and vaccinated intramuscularly with modified IBDV.

Animals↗

Immune dysfunction following infection with chicken anemia agent and infectious bursal disease virus. II. Alterations of in vitro lymphoproliferation and in vivo immune responses.

To determine the functional impact of alterations in lymphocyte concentrations and ratios following infection with chicken anemia agent (CAA) alone or in combination with infectious bursal disease virus (IBDV) on the immune system of young chickens, in vitro lymphoproliferation assays and in vivo responses to vaccination with several common viral agents were assessed at various time intervals post-inoculation (PI). Concanavalin A (Con A), phytohemagglutinin (PHA) and pokeweed mitogen (PWM) stimulation of splenic lymphocytes (SPL) collected from control birds could not be detected until 10-14 days PI. Infection with CAA was characterized by significantly higher PWM stimulation of SPL at 17 days PI and significantly lower PWM stimulation of peripheral blood lymphocytes (PBL) at 14 days PI, compared with uninfected controls. Concanavalin A and PWM stimulation of SPL was significantly increased in birds inoculated with IBDV alone. Lymphocytes harvested from birds inoculated simultaneously with CAA and IBDV had significantly lower responses. Effects on humoral and cell-mediated immunity following CAA and/or IBDV were determined by evaluating vaccination responses to Newcastle disease virus (NDV), fowl pox virus (FPV) and infectious laryngotracheitis virus (ILTV) during the acute phase of CAA infection (2 weeks PI). Vaccination of birds 2 weeks following CAA infection at 1 day of age resulted in decreased protection against NDV (85.7%) and ILTV (7.1%) challenge compared with protection rates in control birds (100% and 53.3% respectively). Infectious bursal disease virus infection was associated with decreased protection against NDV (60%) only. Concomitant infection at 1 day of age resulted in a greater reduction in NDV challenge protection (33.3%), slightly decreased FPV protection (87.5%), increased numbers of persistent FPV vaccination lesions and increased protection against ILTV challenge (71.4%). Vaccination of birds 2 weeks following CAA infection at 2 weeks of age resulted in slightly decreased NDV humoral antibody, development of persistent FPV vaccination lesions (17%) and increased immunity to ILTV challenge compared with control birds (83.3% vs. 66.7%). Chickens inoculated with IBDV alone displayed a more severe depression in NDV antibody titers and only a slight decrease in ILTV protection. Vaccination following concomitant infection at 2 weeks of age resulted in a higher percentage of FPV persistent vaccination lesions (39%) and greatly enhanced immunity to ILTV challenge (100%).

Animals↗

Detection of infectious bursal disease virus infection using the polymerase chain reaction.

The method of reverse transcription (RT) followed by the polymerase chain reaction (PCR) was used to amplify two different fragments of the infectious bursal disease virus (IBDV) genome. Two sets of primer framed two different regions within the genes coding for proteins VP2 and VP3, respectively. Both sequences were detected in five strains of IBDV, whereas, none were obtained from uninfected control cells. The sensitivity of RT-PCR was carried out on nucleic acids from the IBDV infected cell cultures. The detection limit was 10(0) to 10(-1) TCID50 in ethidium bromide stained gels and could be enhanced further to 10(-1) to 10(-3) TCID50 by hybridization after southern transfer. In addition, detection of IBDV infection in 12 out of 14 bursal specimens examined by this technique was shown to be entirely consistent with the clinical history and an alternative diagnostic method. The speed, sensitivity, and specificity of this method is relevant for the diagnosis of infection with IBDV.

Animals↗

Antigen dependent adjuvant activity of a polydispersed beta-(1,4)-linked acetylated mannan (acemannan).

The adjuvant properties of a polydispersed beta-(1,4)-linked acetylated mannan, acemannan (ACE-M), were evaluated. Day-old broiler chicks were randomly selected and allocated to four flocks (Vac 1-4). The Vac 1 flock was sham vaccinated with saline. The Vac 2 flock was vaccinated with an oil-based vaccine (Breedervac III; Newcastle disease virus (NDV), infectious bursal disease virus (IBDV) and infectious bronchitis virus). The Vac 3 flock was vaccinated with a vaccine-ACE-M mixture, and the Vac 4 flock was vaccinated with vaccine and ACE-M at separate anatomical sites. ELISA titres to NDV and IBDV were determined. The immune response to NDV at 21 days postvaccination (PV) was significantly enhanced (P less than or equal to 0.05) by the addition of ACE-M to the vaccine, compared with vaccination without ACE-M. Subsequently, the vaccine-ACE-M mixture appeared to suppress the immune response to NDV. However, at day 35 PV, 95% of the Vac 3 chicks compared with 90% of the Vac 2 and 89% of the Vac 4 chicks exhibited protective titres. The response to IBDV differed from that to NDV. At day 21 PV the immune response to IBDV was essentially the same for all flocks that received vaccine, i.e. addition of ACE-M to the vaccine did not significantly enhance the immune response; however, it did significantly (P less than or equal to 0.05) sustain the immune response at days 28 and 35. In addition to the observed effect on titres to NDV and IBDV, ACE-M also had an effect on flock immunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adjuvants, Immunologic↗

Active and passive protection against variant and classic infectious bursal disease virus strains induced by baculovirus-expressed structural proteins.

Infectious bursal disease virus (IBDV) is responsible for a highly immunosuppressive disease in young chickens which causes significant economic losses to the poultry industry worldwide. The structural protein genes (VP2, VP3 and VP4) of a variant IBDV strain (GLS) were expressed in insect cells using a baculovirus expression system. Susceptible chickens vaccinated with a single dose of the recombinant IBDV antigens were completely protected against challenge with two variant strains of IBDV (GLS and Delaware), and partially protected against the standard challenge strain (STC). A booster dose of the recombinant antigens induced higher levels of neutralizing antibodies and afforded complete protection against both variant and standard virus challenges. Specific-pathogen-free hens vaccinated with a single dose of the same subunit vaccine produced virus-neutralizing antibodies that were capable of passively protecting the progeny from infection with variant IBDV.

Animals↗

Evaluation of FTA paper and phenol for storage, extraction and molecular characterization of infectious bursal disease virus.

Infectious bursal disease virus (IBDV) is an important poultry pathogen and is distributed world wide that can cause immune suppression and lesions of the bursa of Fabricius. The main component of the virus, VP2, is not only responsible for the bird's immune response, but is important for the molecular identification of this virus as well. The nucleic acid of the virus must be adequately preserved to be analyzed by reverse-transcriptase PCR (RT-PCR) and sequenced for the molecular characterization of the field strain. Phenol inactivation has been the standard for IBDV tissue collection and international shipment; however, there have been some reports of interference with molecular detection capabilities when using phenol. Phenol is also a hazardous chemical and must be handled and shipped carefully. The ability to use the Flinders Technology Associates filter paper (FTA card) for inactivation of several avian pathogens has been proven previously, however no work has been published on its use in IBDV nucleic acid detection. Bursas from experimentally infected birds was imprinted on FTA cards, and then placed in phenol. Samples were evaluated and compared based on molecular detection capabilities between the two inactivation methods. The nucleic acid of the virus was detected in 85% of the FTA card inactivated samples compared to 71% in the phenol inactivated samples. Sequence analysis was performed on samples inactivated by both methods and no differences were found. When comparing the RNA stability at different temperatures, euthanized IBDV infected birds were held at two different temperatures before sampling. No differences were detected for FTA sampling; however, for tissues in phenol the nucleic acid was only detectable up to 2 h post-mortem in the tissues held at 4 degrees C prior to sampling. These findings indicate that the FTA card is an efficient and reliable alternative collection method for molecular detection and characterization of IBDV.

Animals↗

L-arginine stimulates immune response in chickens immunized with intermediate plus strain of infectious bursal disease vaccine.

Infectious bursal disease continues to pose an important threat to the commercial poultry industry, especially after the emergence of virulent infectious bursal disease virus (IBDV). L-arginine, a ubiquitous, basic amino acid is used as an immunostimulant in variety of human and animal studies with great success in immunosuppressed hosts. In the present study, we evaluated the immunomodulatory effects of L-arginine on humoral and cellular immune response in chickens immunized with live intermediate plus (IP) strain of IBDV vaccine. Chickens vaccinated with IP strain and supplemented with 2% L-arginine showed 100% protection after challenge with virulent IBDV compared to 80% protection induced by IP strain alone. IP strain vaccine elicited good antibody titres in both the groups, IP + L-arginine and IP alone, however, the antibody titres in IP + L-arginine group were significantly higher (P < 0.05) than IP vaccinated chickens. Mitogenic response of peripheral blood lymphocytes to specific IBDV antigen stimulation was significantly higher in IP + L-arginine group (P < 0.05). Peripheral blood lymphocytes were able to rapidly clear the suppressive effects of IP strain and virulent challenge virus in IP + L-arginine group. These results strongly suggest that l-arginine plays a vital role in modulation of protective immune response against IBDV.

Adjuvants, Immunologic↗

Protection capability of recombinant plasmid DNA vaccine containing VP2 gene of very virulent infectious bursal disease virus in chickens adjuvanted with CpG oligodeoxynucleotide.

In the present study the efficacy of recombinant plasmids DNA vaccine encoding VP2 gene of very virulent strain of infectious bursal disease virus (vvIBDV) isolated from Pakistan was investigated with or without coadministration of cytocine-phosphate-guanine oligodeoxynucleotide (CpG ODN) to protect the chickens against the disease. VP2 gene of vvIBDV was successfully amplified by reverse transcription-polymerase chain reaction (RT-PCR) and was cloned into eukaryotic expression plasmid vector, which consisted of human cytomegalovirus (HCMV) immediate early enhancer and promoter, adenopartite leader sequences and SV-40 polyadenylation signal, and this was designated as pRc-VP2. Seven-day-old maternal antibodies free chickens were intramuscularly injected with 500 microg of pRc-VP2 with or without CpG ODN twice at 1-week interval. At the age of 21 days the broiler chickens were challenged with 10(5) EID(50) of homologous strain of IBDV and observed for 14 days post-challenge. Immunization with pRc-VP2 plus CpG ODN conferred protection in 93% of the chickens as evidenced by the absence of clinical signs, atrophy of bursa of Fabricius (BF) and mortality followed by the group vaccinated with attenuated IBD vaccine and boosted with killed oil based IBDV vaccine, which conferred 90% protection. The protection of chickens injected with pRc-VP2 alone was 67% where as only 20% of the chickens in the negative control group were protected. However, enzyme-linked immunosorbent assay (ELISA) antibody titre in the group vaccinated with pRc-VP2 plus CpG ODN were significantly higher (P<0.05) than the group vaccinated with pRc-VP2 alone as well as the group vaccinated with commercial attenuated IBDV vaccine boosted with commercial oil adjuvanted killed IBDV vaccine. Responsiveness to a mitogenic lectin, phytoheamagglutinin-P was significantly reduced in group immunized with conventional vaccines (live boosted with killed) as compared to all the other groups (P<0.05). The results revealed that co-administration of recombinant plasmids with CpG ODN could protect chickens efficiently from IBDV challenge.

Adjuvants, Immunologic↗

Plasmid DNA encoding antigens of infectious bursal disease viruses induce protective immune responses in chickens: factors influencing efficacy.

The complete polyprotein (VP2/4/3) and VP2 genes of two infectious bursal disease viruses (IBDVs) (one attenuated strain JD1 and one virulent strain ZJ2000) were amplified by long and accurate polymerase chain reaction (LA-PCR), cloned, sequenced and inserted into plasmids pCI and pcDNA3 under the control of human cytomegalovirus (hCMV) immediate early enhancer and promoter. A series of DNA vaccine preparations were made using liposome as the adjuvant to examine their immunogenicity. Although VP2 is the main protective immunogen of IBDV, DNA encoding VP2 initiated a very low level of neutralizing antibody and only protected chickens from clinical outbreak and morality, but not bursal damage. In contrast, DNA encoding VP2/4/3 induced neutralizing antibody and satisfactory protection against virulent IBDV. Recombinant plasmids encoding the polyprotein gene of strain ZJ2000 were more efficient at inducing an immune response than that of strain JD1. Polyprotein expressed by the pCI vector induced better immune response than that expressed by the pcDNA3. Delivery of DNA through intramuscular and/or intradermal routes elicited much higher protective responses than that of oral and eyedrop routes. Most of the chickens vaccinated with high doses of DNA were protected from challenge. Additionally, the immune response to the DNA vaccine was significantly enhanced by a liposome adjuvant. These results indicate that the source of the target genes (from different IBDV strains), the eukaryotic expression vector, the adjuvant, the delivery route and the dosage might play a role of varying degree in influencing the efficacy of the DNA vaccine against IBDV.

Animals↗

Infectious bursal disease virus infection induces macrophage activation via p38 MAPK and NF-kappaB pathways.

In the present study, we show that infection with infectious bursal disease virus (IBDV) causes activation of macrophages, the key cells involved in inflammatory and immune-regulatory functions. Exposure of cultured spleen macrophages (SM) from SPF chickens to IBDV resulted in the production of nitric oxide (NO). In addition, there was upregulation of mRNA expression of inducible nitric oxide synthase (iNOS), IL-8 and cyclooxygenase-2 (COX-2). The signal transduction pathways involved in macrophage activation were examined. The role of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB) was tested by using specific pharmacological inhibitors. Addition of p38 MAPK inhibitor, SB-203580 and NF-kappaB inhibitor Bay 11-7082, suppressed IBDV-induced NO production and mRNA expression of iNOS, IL-8 and COX-2. The results suggest that IBDV uses cellular signal transduction machinery, in particular the p38 MAPK and NF-kappaB pathways, to elicit macrophage activation. The increased production of NO, IL-8 and COX-2 by macrophages may contribute to bursa inflammatory responses commonly seen during the acute IBDV infection.

Animals↗

Demonstration of receptor binding properties of VP2 of very virulent strain infectious bursal disease virus on Vero cells.

Tissue culture adaptation of infectious bursal disease virus (IBDV) results in alternation of three residues on its major capsid protein VP2 and these residues may engage in receptor binding. Although the key of successful infection of tissue culture adapted IBDV in tissue cultures was defined as the virus entering steps, mechanism of the adaptation is poorly understood. In this study, recombinant VP2s of an attenuated strain (D78) and a very virulent strain (HK46) of IBDV tagged with rabbit immunoglobulin G heavy chain were expressed in mammalian cells, generating RAVP2 and RVVP2, respectively, in high purity. Using flow cytometry, both RAVP2 and RVVP2 were demonstrated to bind with Vero cells while these bindings were blocked by D78 viral particles, implying both very virulent IBDVs (vvIBDVs) and attenuated IBDVs bind to Vero cells through the same receptor(s). Since vvIBDVs cannot be propagated directly in tissue cultures, the specific binding between RVVP2 and Vero cells suggests the barrier for tissue culture adaptation may be beyond the virus attachment process.

Adaptation, Physiological↗

A novel technique for in-vivo assay of viral regulatory regions in genomes of animal RNA viruses.

A novel in-vivo assay system for mapping and analyzing regulatory signals which promote transcription and expression of viral RNA genomes is described. The system was developed using infectious bursal disease virus (IBDV), a double-stranded RNA virus and Vero cells which are permissive for IBDV, as a model. The model system consisted of engineered modifications of an enhancer-less pGL3-Promoter vector such that deleted lengths of the 5' noncoding region of genome segment A of IBDV were positioned in either the plus-sense or the minus-sense orientation immediately downstream of the SV40 promoter and upstream of the luciferase (LUC) reporter gene. Transient transfections of these constructs in IBDV-infected and uninfected Vero cells resulted in endogenous generation of recombinant viral RNA-LUC containing the 5' terminal viral RNA sequences in either the plus-sense or the minus-sense orientation. LUC assays of the Vero cell lysates allowed the localization of promoter activity in the 5'-terminal 32 base pairs of genomic segment A of IBDV. Because the viral RNA transcripts produced in-vivo can be either plus-sense or minus-sense, the system can be used to assay for regulatory regions for transcription or replication for any animal RNA virus.

Animals↗

DNA-mediated vaccination against infectious bursal disease in chickens.

The objective of the present study was to investigate the feasibility of a DNA vaccine to protect chickens against infectious bursal disease virus (IBDV) infection. A plasmid DNA carrying VP2, VP4, and VP3 genes of the standard challenge (STC) strain of IBDV was constructed and designated as pCR3.1-VP243-STC. One-day-old chickens were intramuscularly injected with the plasmid pCR3.1-VP243-STC once (group D1), twice (group D2), or three times (group D3) at weekly intervals. Chickens at 3 weeks old were orally inoculated with IBDV strain STC and observed for 10 days after challenge. Immunization twice (group D2) or three times (group D3) with the plasmid pCR3.1-VP243-STC conferred protection for 50-100 or 80-100% of chickens, respectively, as evidenced by the absence of clinical signs, mortality, and bursal atrophy. Although chickens vaccinated once (group D1) with the plasmid pCR3.1-VP243-STC did not have clinical signs, they exhibited varying degree of bursal atrophy after challenge. Enzyme-linked immunosorbent assay (ELISA) antibody titers in chickens protected by the plasmid pCR3.1-VP243-STC were significantly lower (P<0.05) than those not protected 10 days after challenge. IBDV antigen was not detected in the bursae of chickens that were protected by receiving the plasmid pCR3.1-VP243-STC twice or three times. The results indicate that the constructed plasmid pCR3.1-VP243-STC as a DNA vaccine provided efficacious protection for chickens against IBDV infection.

Animals↗

Development of a vaccine for immunization against classical as well as variant strains of infectious bursal disease virus using reverse genetics.

Available IBDV vaccines based on classical IBDV strains do not induce full protection in the presence of maternally derived antibodies (MDA) against variant strains. The aim of this study was the generation of an IBDV chimera between both classical and variant strains. Characterization of the generated chimeric IBDV (D78-Chim) was performed in both cell culture and susceptible chickens using the classical vaccine strain D78 for comparison. Growth kinetics on cell culture showed that the D78-Chim replicates comparable to the live vaccine strain D78. Administration of the D78-Chim to SPF chickens resulted in equally high virus neutralizing antibodies titres against both, classical and variant IBDV strains. In vivo experiments in commercial chickens revealed that D78-Chim and D78 induced comparable bursal damage in presence of maternally derived antibodies. Both D78-Chim and D78 viruses were able to breakthrough a similar level of MDA.

Animals↗

Development and large-scale use of recombinant VP2 vaccine for the prevention of infectious bursal disease of chickens.

Infectious bursal disease virus (IBDV) is the causative agent of Gumboro disease, an infectious disease of global economic importance in poultry. One of the most effective types of inactivated IBDV vaccine is produced by infecting young chickens with a virulent strain, sacrificing them and extracting the virus from the bursa of Fabricius. The goal of this study was to produce an effective subunit vaccine against IBDV thereby providing an effective means of combating the disease. In areas in which the bursa-derived vaccine is in use, this subunit vaccine would eliminate the use of live birds for the production of inactivated vaccines. The gene for viral protein 2 (VP2) of IBDV was cloned into a Pichia pastoris expression system. This efficient system allowed us to meet the need for inexpensive vaccines required by the poultry industry. Following expression and scale-up, the protein was used to vaccinate chickens, against either Gumboro disease alone or in combination with inactivated Newcastle disease virus (NDV). Full protection was conferred against IBDV following vaccination with the subunit recombinant vaccine. No untoward influence on the response to the NDV vaccine was recorded. Over 250 million birds have already been vaccinated with this vaccine. The advantages of a subunit vaccine over an inactivated one are discussed. This approach will enable rapid adjustment to new virulent strains if and when they appear.

Animals↗

The characterization of infectious bursal disease virus strains/isolates from field outbreaks in India.

Three infectious bursal disease virus (IBDV) isolates were adapted to culture in chick embryo fibroblast cells in which they produced a cytopathic effect. The isolates were identified as IBDV by virus neutralization tests using a standard hyperimmune serum against infectious bursal disease, physicochemical properties and their pathogenicity in chick embryos and chicks. The IBDV S394 strain was antigenically different from IBDV S194/IBDV S494 as well as from the IBDV Intermediate Georgia strain, one of the vaccine strains in use in India.

Animals↗

Antigenic and molecular characterization of recent infectious bursal disease virus isolates in China.

Eleven infectious bursal disease virus (IBDV) strains isolated recently from China were compared with the early classical virulent strain CJ801, the chicken embryo fibroblast-adapted (CEF) variant strain GZ902, and the attenuated vaccine strains BJ836, BK912, and LM to discern the evolutionary characteristics of IBDV in China at both antigenic and genetic levels. Virus neutralization (VN) assay showed that all ten very virulent (vv) IBDV strains belong to the same subtype as attenuated strains, whereas the other variant isolate strain BX could be attributed to other subtype of the variant strain GZ902. Antigen-capture ELISA (AC-ELISA) determined by a panel of monoclonal antibodies (Mabs) against classical and variant strains showed further that among these vv strains, nine strains except for strain NC had no reaction with neutralizing Mab B69. The vv strains SC and YV had no reaction with non-neutralizing Mabs 2B8 and 2C4, respectively, whose epitopes were located in classical IBDV strains. On the other hand, there is no alteration in antigenic epitopes located in the variant strain BX as that of the variant GZ902. Sequence comparison of the highly variable region (HVR) of the VP2 proteins showed that these vv strains had 98.6-100.0% identities to European and Asian vv strains at amino acid level. For the vv strains NC, SC, and YV, all had one amino acid substitution at the major hydrophilic domains, indicating that new vv strains are evolving. In addition, the vv strains DMS and NC had amino acid residue 279N as well, showing that the substitution of amino acid at this position might not be related to the virulence of IBDV. The variant strain BX had one amino acid substitution in the two major hydrophilic domains and two unique amino acids 249K and 254S as the other early variant strains, and shared 97.3% of amino acid identity to the variant strain VarE. Phylogenetic analysis suggests that the recent Chinese vvIBDVs and the previous European and Asian vv strains still belong to a genetic group and the variant strain BX to the other genetic group, which is more closely related to the European classical virulent strain F52/70 and the American classical virulent strain STC than to the early Chinese classical virulent strain CJ801, showing that the recent vv and variant strains that spread widely in the country might be derived from Europe and America than from early Chinese classical virulent strains.

Amino Acid Sequence↗

Recent trends in the molecular diagnosis of infectious bursal disease viruses.

Infectious bursal disease virus (IBDV) causes an immunosuppressive disease in young chickens. Two serotypes of this double-stranded RNA virus exist but only serotype 1 viruses cause disease in chickens. Detection and strain identification of IBDV is important because antigenic subtypes found within serotype 1 make it necessary to tailor vaccination programs to the antigenic type found in the bird's environment. Because conventional virus isolation and characterization are not practical for routine diagnosis of IBDV, antigen-capture enzyme-linked immunosorbent assay (ELISA) and molecular assays based on reverse transcription-polymerase chain reaction (RT-PCR) technology were developed. Compared with antigen-capture ELISA, RT-PCR assays have greater versatility and are more sensitive and specific. Strain identification has been accomplished using a variety of post-RT-PCR assays, including restriction enzyme digestion of the RT-PCR products. The resulting restriction fragment length polymorphisms (RFLP) are used to differentiate viruses into molecular groups that correlate with antigenic and pathogenic types. Recently, two types of real-time RT-PCR have been used to identify and differentiate strains of IBDV. Both methods use distance-dependent interaction between two dye molecules, known as fluorescence resonance energy transfer (FRET). The dye molecules are attached to one or more nucleotide probes that detect specific nucleotide sequences of the virus. Our laboratory has used a two-probe assay to identify single-nucleotide mutations among IBDV strains. A mutation probe is used in this assay to detect substitution mutations in a region of the viral genome that encodes a neutralizing epitope of the virus. These assays are accurate, reliable and inexpensive compared with conventional RT-PCR because they do not require RFLP or other labor-intensive post-RT-PCR assays to distinguish viral strains.

Animals↗