Immunosuppressive effect of infectious bursal disease virus strains of variable virulence for chickens.

Infection of chicks with attenuated Lp and Sp clones of the RF-1 strain of infectious bursal disease virus was shown to exert no immunosuppressive effect, whereas the parent strain RF-1tc and the original virulent strain RF-1wt were immunosuppressive. One-day-old chicks infected with Lp and Sp clones showed no suppression of immunological response to live Newcastle disease vaccines B1 and TCND, and to bivalent infectious coryza vaccine. On the other hand, infection with RF-1tc or RF-1wt strains was immunosuppressive for these vaccines. The immunosuppressive effect of RF-1tc and RF-1wt strains was more pronounced for infectious coryza vaccine and B1 vaccine than for TCND vaccine. The immunosuppressive effect of RF-1tc and RF-1wt strains was lower when chicks were infected with these strains at the age of 21 days than when they were infected at one day of age.     

Baculovirus virions displaying infectious bursal disease virus VP2 protein protect chickens against infectious bursal disease virus infection

Infectious bursal disease (IBD) is an acute and contagious viral infection of young chickens caused by IBD virus (IBDV). The VP2 protein of IBDV is the only antigen for inducing neutralizing antibodies and protective immunity in the natural host. In the current study, we have succeeded in construction of one recombinant baculovirus BacSC-VP2 expressing His6-tagged VP2 with the baculovirus envelope protein gp64 transmembrane domain (TM) and cytoplasmic domain (CTD). The His6-tagged recombinant VP2 was expressed and anchored on the plasma membrane of Sf-9 cells, as examined by western blot and confocal microscopy. Immunogold electron microscopy demonstrated that the VP2 protein of IBDV was successfully displayed on the viral surface. Vaccination of chickens with the VP2-pseudotyped baculovirus vaccine (BacSC-VP2) elicited significantly higher levels of VP2-specific enzyme-linked immunosorbent assay antibodies and neutralizing antibodies than the control groups. IBDV-specific proliferation of lymphocytes was observed in chickens immunized with the recombinant BacSC-VP2. An in vivo challenge study of the recombinant baculovirus BacSC-VP2 showed effective protection against a very virulent (vv) IBDV infection in chickens. In addition, mortality and gross and histopathological findings in the bursa demonstrated the efficacy of the vaccine in reducing virulence of the disease. These results indicate that the recombinant baculovirus BacSC-VP2 can be a potential vaccine against IBDV infections.     

Effects of standard and variant strains of infectious bursal disease virus on infections of chickens

T-cell-mediated and humoral immune responses were measured in chickens infected with standard and variant strains of infectious bursal disease virus. One-day-old and 3-week-old chickens were infected with these viruses and then given sheep RBC, killed Brucella abortus strain 19, and Newcastle disease virus. Appropriate serologic tests were used to monitor the primary and secondary responses to the antigens. Lymphoblast transformation assays were performed weekly. The response to the infectious bursal disease virus was determined by virus neutralization tests, microscopic examination of bursas, and bursal to body weight ratios. One-day-old chickens had T-cell-mediated and humoral immune suppression with both strains of virus, compared with controls. The lymphoblast transformation responses indicated that the variant strain was significantly (P less than 0.05) more suppressive than the standard strain. Three-week-old chickens had humoral immune suppression with the standard strain, but not with the variant strain. The lymphoblast transformation response was transiently suppressed at this age by the variant strain only. During the first week of infection, 1-day-old and 3-week-old chickens had lower neutralizing antibody titers to the variant strain than to the standard strain.     

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.     

Lysis of myelocytes in chickens infected with infectious bursal disease virus

In specific-pathogen-free chickens infected with the highly virulent HPS-2 strain or virulent reference GBF-1 strain of infectious bursal disease virus (IBDV), pathologic changes of the bone marrow were investigated. On histologic examination, bone marrow lesions were prominent in the HPS-2 group but only mild in the GBF-1 group. The bone marrow of the HPS-2 group showed severe lysis and depletion of heterophil myelocytes with pyknotic nuclear alteration 2-3 days after inoculation. On examination with an electron microscope, heterophil myelocytes were characterized by shrinkage of the cytoplasm and peripheral condensation of nuclear chromatin. IBDV particles were not detected in altered myelocytes. A terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling method demonstrated a positive reaction in only heterophil myelocytes. In contrast, nucleosomal DNA fragmentation in HPS-2-infected bone marrow cells was indiscernible by agarose gel electrophoresis. These findings indicate that lysis of bone marrow cells is selectively induced in heterophil myelocytes at an early stage after IBDV infection and independent of virus replication.     

Experimental cryptosporidiosis and infectious bursal disease virus infection of specific-pathogen-free chickens

Specific-pathogen-free chickens orally inoculated at 4 days of age with a moderately pathogenic vaccine strain of infectious bursal disease virus (IBDV) and/or at 5 days of age with Cryptosporidium baileyi oocysts remained free of overt clinical signs throughout a 16-day period postinoculation (PI). The prepatency period for C. baileyi oocyst shedding was shorter in chickens receiving higher numbers of oocysts, but once shedding was detected, there were no obvious differences in shedding patterns among groups receiving 10(3) through 10(6) oocysts. On days 8 and 16 PI, cryptosporidia were located primarily in the bursae of Fabricius. IBDV exposure was associated with bursal follicle atrophy, whereas C. baileyi infection resulted in bursal epithelial hypertrophy and hyperplasia, mild follicle atrophy, and heterophil infiltration of the bursal mucosa. Examination of experimental groups of 30 birds each indicated that concurrent infection with both agents resulted in more severe bursal lesions, more infected birds, and greater numbers of cryptosporidia in infected tissues. At the termination of the trial, 16 days PI, Cryptosporidium infection was associated with a 6% decrease in mean body weight compared with controls.     

Comparative immunopathogenesis of mild,intermediate, and virulent strains of classic infectious bursal disease virus

Differences in the immunopathogenesis of several strains of infectious bursal disease virus (IBDV) were compared. The strains included a virulent virus (IBDV-IM) and three vaccine viruses that included an intermediate vaccine virus (IBDV-B2) and two mild vaccine viruses (IBDV-Lukert and IBDV-BVM). The most significant differences were found in the systemic effects of these strains. In comparison with other strains, IBDV-IM antigen was detectable for up to 8 days postinfection (PI) in lymphoid tissues that included spleen and cecal tonsils, whereas only a few IBDV-B2- and IBDV-Lukert- and no IBDV-BVM-inoculated birds had detectable IBDV antigen in these tissues. IBDV-IM induced systemic circulating nitrite levels in over 86% of the birds at days 2 and 3 PI. IBDV-IM suppressed most vigorously the splenic mitogenic response on days 3-8 PI. Among the three vaccine strains, IBDV-B2 was the most virulent of the three, inducing a significant suppression of the mitogenic response (P < 0.05) and the most vigorous lesions in the bursa of Fabricius with the highest possible lesion score of 4 at 3 days PI (P < 0.05). IBDV-BVM was the mildest strain, not inducing any detectable lesions in lymphoid tissue at the tested time points. Whereas all IBDV-BVM-inoculated and 67% and 33% of the IBDV-Lukert- and IBDV-B2-inoculated birds, respectively, had detectable IBDV antigen in the bursa at 4 days postchallenge, none of the IBDV-IM-inoculated birds was positive for IBDV by immunohistochemistry. IBDV-IM induced the highest enzyme-linked immunosorbent assay (ELISA) antibody levels detected at days 8-29 PI (P < 0.05) and the best protection against challenge virus replication in comparison with IBDV-B2 and IBDV-Lukert. Only one of five IBDV-BVM-inoculated birds developed anti-IBDV ELISA antibodies at 29 days PI, and none of the birds was protected against IBDV challenge. We speculate that better protection with more virulent strains was due to more systemic antigenic stimulation on the basis of higher replication of IBDV in extrabursal lymphoid tissues. Interestingly, IBDV-IM did not differ from IBDV-B2 and IBDV-Lukert in its ability to induce T cell accumulation in the bursa at 8 days PI and local interferon-gamma induction from days 2 to 5 PI. These results suggested that the local T cell events in the bursa alone may not be indicative of a rapid and protective immune response.     

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.     

Isolation of cytopathogenic strains of infectious bursal virus of chickens in cell cultures

Five virus strains with cytopathogenic properties for the cell cultures of chick embryo fibroblasts and embryo kidney cells were isolated from chickens clinically suspected of suffering from infectious bursitis. According to the form of cytopathic effect (CPE) on cell cultures, according to chloroform and thermal resistance, nature of nucleic acid (RNA), according to the absence of the production of intracellular inclusions, negative haemagglutination, and according to antigenic identity with the reference strain, the isolates were deemed to belong to the viruses of infectious bursitis. This conclusion was also corroborated by histological and serological studies in isolates of infected experimental animals.     

鸡传染性喉气管炎的防治

传染性喉气管炎(ILT)是由A型疱疹病毒引起的鸡的一种急性呼吸道传染病。1936年由Beaudette首次证明其病原是一种滤过性病毒。目前此病在许多国家广泛流行,是危害养鸡业的重要疾病,近几年来,在我国一些养鸡集中的地区,ILT引起产蛋鸡产蛋下降和鸡群的高死亡率,产蛋率一般下降10%～50%,死亡率一般在5%～70%之间,给养鸡业带来巨大经济损失,现将实践中对该病的诊断、治疗经验及防制要点总结如下。1流行特点鸡是ILT感染的主要自然宿主,各种日龄的鸡均可感染,以4～10月龄的成年鸡最为严重,对产蛋高峰期的鸡特别易感且危害大;从鸡品种来看,以褐…     

Serological investigations of infectious bursal disease virus and reticuloendotheliosis virus infections in New Zealand chickens

Extract

Sir:- Between 1975 and 1981, sera were collected from 89 New Zealand chicken farms representing a variety of laying and meat birds of different ages from both primary breeders and commercial flocks. In some instances samples were collected from one or more flocks on a farm. In most cases between ten and 20 birds were sampled in a flock and the sera pooled to give a composite sample for testing.     

Age resistance in chickens against infectious bursal disease

The day old broiler chickens possessing IBD precipitating maternal antibody when exposed either to IBD contaminated environment or challenged intrabursally with virulent virus at weekly intervals indicated 100% susceptibility around 4–5 weeks of age. However, chickens lacking maternal antibody upon intrabursal challenge were found susceptible by 2 weeks of age.     

Immunogenicity and antigenicity of infectious bursal disease virus serotypes I and II in chickens

Chickens were inoculated with infectious bursal disease virus serotype I or serotype II to determine if their immune system can distinguish between the two serotypes. Chickens had neutralizing antibodies to only serotype I viruses following exposure to serotype I viruses, and chickens had antibodies to only serotype II viruses following exposure to serotype II viruses. No cross-reactions were observed between antisera prepared to each of these two serotypes using a cross-virus-neutralization assay. Signs of disease were detected only in birds exposed to a virulent serotype I isolate. Chicks exposed to the serotype II viruses were not protected from challenge with a virulent serotype I isolate. In one experiment, antibodies to a serotype II isolate, which were detected before challenge, did not protect chicks from challenge with a virulent serotype I isolate.     

Dexamethasone reduces infectious bursal disease mortality in chickens

Very virulent infectious bursal disease virus (vvIBDV) causes high mortality in chickens but measures to reduce the mortality have not been explored. Chickens (8–9 weeks) were treated with 3 agents before and during vvIBDV inoculation. Dexamethasone treatment reduced the mortality of infected chickens (40.7% vs. 3.7%; p < 0.001), but treatment with aspirin or vitamin E plus selenium did not affect the mortality. The bursa of Fabricius appeared to have shrunk in both dead and surviving chickens (p < 0.01). The results indicate that dexamethasone can reduce mortality in vvIBDV-infected chickens and may provide therapeutic clues for saving individual birds infected by the virus.