Immunoreactivity and morphological changes of bursal follicles in chickens infected with vaccine or wild-type strains of the infectious bursal disease virus

Infectious bursal disease (IBD) is characterized by immunosuppression due to the depletion of lymphocytes in the atrophied bursa of Fabricius (BF). We have sometimes encountered contradictory findings: chickens infected with the vaccine IBD virus (IBDV) strain have sometimes exhibited a highly atrophied BF, but not immunosuppression. In this study, chickens administered vaccine or wild-type strains of IBDV were later vaccinated with the B1 strain of the Newcastle disease virus (NDV). Bursal changes were examined histologically with a focus on the bursal follicle. The immunoreactivity to NDV was also evaluated with the hemagglutination inhibition test. In gross examination, we observed a few chickens with a severely atrophied BF in vaccine strain-administered groups (vaccine groups), and the level of severity was the same as that in the wild-type strain-administered group (wild-type group). However, these chickens retained humoral antibody responses to NDV and were revealed to possess a higher number of bursal follicles than those of the wild-type group. These results indicated that macroscopic evaluation dose not accurately reflect the immunoreactivity and degree of bursal damage in IBDV-administered chickens. We also found non-immunosuppressed chickens in the wild-type group. These non-immunosuppressed chickens retained a significantly higher number of normal follicles and total follicles according to our statistical analysis. Furthermore, a high correlation coefficient between the NDV-HI titer and the number of normal follicles was found in the wild-type group. These results implied that the retained number of normal follicles is important for the immunoreactivity of chickens infected with IBDV.     

鸡传染性法氏囊病病毒地方流行毒株的免疫原性

从河北省一些发病鸡场分离到JD1～JD10共10株鸡传染性法氏囊病病毒(IBDV)毒株,用IBD标准阳性血清以琼扩试验进行了初步鉴定.并进行了IBDV分离物及其鸡胚适应毒免疫原对标准强毒IBDV-BC6/85株免疫保护试验,D78弱毒疫苗对IBDV各分离毒株的免疫保护试验以及分离毒株间交互免疫保护试验.结果表明,D78疫苗对JD2,JD5和JD10 IBDV分离株的保护率较低,分别为40%、50%和60%.分离毒株JD5、JD2及其鸡胚传代物E-JD2对强毒株的免疫保护率可达100%.交互免疫保护试验表明,JD2对其余各分离株的免疫保护指数达到80%以上,对标准强毒株和地方分离株均可产生有效免疫保护.     

Effects of two infectious bursal disease vaccine virus strains on hepatic microsomal enzyme activities in chickens

The influence of two infectious bursal disease vaccines on the activities of hepatic microsomal enzymes aniline hydroxylase, ethylmorphine N-demethylase, NADPH-cytochrome c reductase, aryl sulphotransferase and p-nitrophenol UDP-glucuronyltransferase was investigated in chickens. The vaccines contained attenuated Winterfield 2512 and VMG-91 strains, respectively. The activities of enzymes were determined on postvaccination days 0, 2, 5 and 7. At the same time, post-mitochondrial supernatant, cytosolic and microsomal pellet protein concentrations were determined. As expected, the antibody titres against infectious bursal disease virus in the serum were increased in both tested groups in relation to each administered vaccine. Using RT-PCR, the presence of the VP2 gene fragment of virus in the liver of chicken was demonstrated 4 and 6 h after vaccination. The results of this study suggest that the two commercial vaccines modulate the activities of five enzymes tested, and that the two attenuated vaccines applied triggered induction and/or inhibition of phases I and II of biotransformation enzyme activities.     

Studies on a vaccine against infectious bursal disease

An infectious bursal disease vaccine, registered for use in breeder flocks, was studied for efficacy on the day-old offspring of vaccinated hens and for virulence in susceptible day-old and 6-week-old chickens. When given to susceptible day-old chicks and 6-week-old cockerels, the vaccine was found to induce atrophy and pathology of the bursa of Fabricius similar to that observed in field infections. Chicks vaccinated at day-old had markedly lowered titres in the haemagglutination inhibition test to Newcastle disease virus, when this was given 2 weeks later, but the response of the 6-week-old cockerel was similar to that of control birds. Maternal antibody induced by the vaccine protected chicks against infection at day-old.     

Duration of immunosuppression caused by a vaccine strain of infectious bursal disease virus

The depression of response of Brucella abortus strain 19 caused by an infectious bursal disease vaccine virus given to chicks at one day old was shown to persist for four weeks. Histological examination of the bursa of Fabricius showed a gradual repopulation by bursal lymphocytes, after initial damage, concomitant with the development of a humoral response.     

Antigenic diversity of infectious bursal disease viruses

Statistically significant antigenic differences were detected among serotype I infectious bursal disease viruses (IBDV) using the virus-neutralization test. Eight serotype I commercial vaccine strains, five serotype I field strains, and two serotype II field strains were tested. Hyperimmune guinea pig antisera against heterologous and homologous IBDV strains were used in cross-neutralization tests. Relatedness values were calculated from geometric mean antibody titers based on a minimum of three tests. Six subtypes were distinguished among the 13 serotype I strains tested.     

Structural proteins of classic and variant strains of infectious bursal disease viruses.

Structural polypeptides of six tissue-culture-origin (BGM-70 continuous cell line) infectious bursal disease viruses representing classic and variant strains of serotype 1 and one serotype 2 strain were analyzed and compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Additionally, two of the variant strains were propagated in vivo in bursa of Fabricius and compared with those grown in cell culture. Differences among the structural proteins of serotype 1 viruses were minor and probably of no value in differentiating these viruses. However, distinct differences were observed between serotype 1 and 2 viruses. The bursa-derived viruses were different from those propagated in cell culture in molecular weights and in proportions of the proteins. The bursa-derived strains had protein migration patterns similar to those described for tissue-culture-incomplete virus particles.     

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.     

The use of gamma irradiation for the inactivation of infectious bursal disease viruses

The maximum dosage of gamma irradiation approved by the U.S. Food and Drug Administration (FDA) for poultry is 3.0 kiloGrays (kGy). This treatment is designed to reduce bacterial contamination on uncooked poultry carcasses and meat products. The possible presence of infectious bursal disease virus (IBDV) on poultry postharvest has prompted some countries to study the risk associated with introducing nonnative strains of the virus from imported commodities. The goal of this study was to determine if this risk could be reduced using gamma irradiation to inactivate IBDV. At the dosage approved by the FDA, the titers of IBDV vaccine strains were reduced between 0 and 1 log10. Titers of the pathogenic IBDV strains tested were not reduced after the 3.0 kGy exposure. Furthermore, titers of pathogenic viral strains were not reduced following exposure up to 5.0 kGy. As the exposure to gamma irradiation increased, the titers of the vaccine strains decreased. At the maximum dosage tested (10 kGy), the 89/03 variant virus vaccine was completely inactivated. Titers of the three classic IBDV vaccine strains were reduced between 1.6-2.0 logs after the 10 kGy exposure; however, these viruses remained viable after this treatment. Gamma irradiation is not an effective intervention to reduce the risk of IBDV introduction via processed poultry.     

The use of biotin-labeled cDNA probes for the detection of infectious bursal disease viruses

A cDNA library was prepared from the double-stranded RNA genome of the infectious bursal disease virus (IBDV) strain ST-C. The cDNA molecules were annealed into the plasmid pUC9 and used to transform Escherichia coli strain JM107. A cDNA clone that contained IBDV-specific nucleotide sequences was selected and designated STC-1. Radiolabeled probes were prepared from STC-1 and hybridized to genome segment A of ST-C in a northern blot hybridization assay. The STC-1 cDNA was 448 base pairs in length, and its nucleotide sequence indicated that it is located near the VP-2/VP-4 junction in IBDV genome segment A. Biotin-labeled probes were prepared from STC-1 and used in a dot-blot hybridization assay to detect IBDV. Under relatively low stringency conditions of hybridization, the biotinylated probes detected four subtypes of IBDV serotype 1 and a serotype 2 IBDV isolate.     

Immunogenicity of infectious bursal disease viruses in chickens.

Cross-protective properties of infectious bursal disease viruses (IBDVs) were studied. Viruses represented different subtypes of serotype 1, including recently isolated viruses (variants), and a serotype 2 virus. Chickens were vaccinated at 3 weeks of age with inactivated vaccines containing 10(5), 10(6), 10(7), or 10(8) mean tissue-culture infectious dose of a given virus and challenged 2 weeks later using either 10(2) or 10(3.5) mean embryo infectious dose (EID50) of either a standard virus or a variant serotype 1 virus. Protection was evaluated at 5 and 10 days post-challenge, based on gross and microscopic lesions, body weight, and bursa/body-weight ratios. The serotype 2 virus did not confer protection on birds challenged with the serotype 1 viruses. Vaccines made of variant viruses at the low doses protected chickens challenged with the high or low doses of either the standard or the variant viruses. Vaccines made of the standard or variant strains at low doses protected against high or low challenge doses of the standard strain. Vaccines made of the high dose of any of the standard strains protected chickens against the variant virus when the low challenge dose (10(2) EID50) was used, but not when the high challenge dose (10(3.5) EID50) was used. The lowest dose of the standard viruses vaccines required to confer protection against the variant virus varied depending on the strain. Results indicated that protection depended on the strain and dose of both the vaccine and challenge viruses and that the variant strains and standard strains share a common protective antigen(s).