由法氏囊病毒引起鸡的免疫抑制

1法氏囊 禽类法氏囊是雏鸡免疫系统的中枢免疫器官.它是鸟类特有的免疫器官,所以值得特别关注.许多研究已搞清了其生理学作用.雏鸡前3周是法氏囊快速发展时期,在这个时期法氏囊迅速增殖,3周龄后法氏囊就逐渐退化,研究表明,大约在12周龄,法氏囊就完全退化.     

Immunosuppression induced by infectious bursal disease virus.

Immunosuppression caused by infectious bursal disease virus (IBDV) is of major interest because of the widespread occurrence of the infection in commercial chickens. Infection with IBDV at an early age significantly compromises the humoral and local immune responses of chickens. The cellular immune response is also compromised by apparently to a lesser extent and for a short period. The immunosuppression seems to be a result of direct effect (lysis) of B cells or their precursors. Other mechanisms of immunosuppression have been suggested, notably the development of suppressor cells.     

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.     

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.     

Effect of in ovo administered reovirus vaccines on immune responses of specific-pathogen-free chickens

We investigated the effect of in ovo administered reovirus vaccines on the immune responses of specific-pathogen-free chickens. T-cell mitogenic responses to concanavalin A were numerically lower at 9 and 12 days of age and significantly lower at 6 days of age in birds vaccinated with a commercial reovirus vaccine compared with unvaccinated birds or birds vaccinated with an experimental reovirus-antibody complex vaccine. There were no significant differences in proportions of subpopulations of helper (CD4+CD8-) or cytotoxic (CD4-CD8+) T cells except at 12 days of age, when the percentages of CD4-CD8+ cells in the two vaccinated groups were statistically higher than in the nonvaccinated group. B-cell populations were not different among vaccine groups except at 9 days of age, when the vaccinated groups had the highest level of B cells. This commercial reovirus vaccine should not be given in ovo to embryos having little or no maternal antibody, otherwise immunosuppression may occur in the chicks. The addition of the antibody complex to the vaccine prevented this T-cell immunosuppression.     

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).     

Efficacy of live vaccines against serologic subtypes of infectious bursal disease virus

Experiments determined the efficacy of live vaccines in specific-pathogen-free broilers against serologic subtypes of infectious bursal disease virus (IBDV). Challenge isolates were the Delmarva variant E, a standard serotype I (APHIS) and a variant isolate from Mississippi. The vaccines were a cloned standard (CS) vaccine (Clone Vac-D78), a cloned variant (CV) vaccine (Bursa Vac IV), and an uncloned standard (UCS) vaccine (Bursine II). The severity of microscopic lesions was correlated with bursal atrophy as measured by bursa-weight-to-body-weight ratios. All vaccines provided adequate protection against the APHIS challenge. The three vaccines averaged 77% protection against APHIS in the first experiment and 78% in the second. Protection against the variant E and Miss isolates was considerably less for all vaccines. The three vaccines produced an average 70% protection against the Miss isolate in the first experiment and 69% in the second experiment. Against the variant E virus, the three vaccines averaged 67% protection in the first experiment and 65% in the second. There were significant differences in protection for each vaccine against individual IBDV subtypes. Results showed that no vaccine provided good protection (at least 80%) against all three subtypes of IBDV.     

Protective efficacy of intermediate and intermediate plus infectious bursal disease virus (IBDV) vaccines against very virulent IBDV in commercial broilers

The evolution of very virulent (vv) infectious bursal disease virus (IBDV) has led to significant economic losses in many poultry-producing areas. Despite vigorous vaccination strategies, IBDV has been difficult to control. The protective efficacy of IBDV vaccines is traditionally evaluated in specific pathogen-free (SPF) chickens. But under field conditions, residual maternal antibody (mAb) levels may interfere with vaccine efficacy. In this study, commercial broilers with various levels of maternally derived antibodies were vaccinated with IBDV vaccines of different virulence (vaccines 1-3, intermediate; vaccine 4, intermediate plus). At an average maternal virus-neutralizing antibody (mAb) level of log2 10.8 (range 7.6-11.6) at day of vaccination, only the intermediate plus vaccine induced IBDV antibodies after 18 days, while the other intermediate vaccines did not. At average mAb levels of log2 6.7 (range 5.6-8.6) at day of vaccination, all vaccines induced circulating antibodies, although the onset of antibody production differed significantly between strains (P < 0.05). While the intermediate plus vaccine induced enzyme-linked immunosorbent assay antibody levels already at 14 days postvaccination (PV), the intermediate vaccines induced significant antibody levels 28 (vaccines 1, 2) and 35 (vaccine 3) days PV. The time of IBDV antibody induction correlated with the onset of bursa lesions. The severity of lesions was comparable between vaccines 1, 3, and 4 (lesion score 4), while vaccine 2 induce only mild lesions of score 1 in 23% of the tested birds. Despite the induction of antibodies, none of the tested vaccines fully protected against challenge with vvIBDV. All challenged birds had either significantly higher bursal lesion scores or a higher IBDV antigen load in the bursa or sometimes both in comparison with nonchallenged birds (P < 0.05). Our study demonstrates that the evaluation of IBDV-vaccine efficacy is difficult in commercial broilers. For the first time, it was shown that the onset of bursa lesions and recovery of IBDV-vaccinated broilers is delayed in the presence of mAb in comparison with SPF chickens but not suppressed as previously assumed. At the time of challenge, vaccinated birds may still have significant bursa lesions and may lack target cells for IBDV-challenge virus. To be able to evaluate vaccine efficacy in commercial broilers, parameters such as intrabursal IBDV-antigen load should also be considered in conjunction with bursa lesion scores.     

Pathogenicity of recent isolates of infectious bursal disease virus in specific-pathogen-free chickens: protection conferred by an intermediate vaccine strain

The pathogenicity of recent isolates of infectious bursal disease virus and the protection conferred against them by a commercial vaccine strain of intermediate virulence were examined in specific-pathogen-free chickens. Based on clinical signs, mortality, and macroscopic lesions in susceptible chickens, the isolates designated as A-Delmarva and U-28 were distinct from a previously known serotype I virulent isolate (Edgar). Histopathological analysis of the bursa of Fabricius did not establish differences between the field isolates. Although the vaccine strain produced some degree of bursal damage in antibody-free chickens, it was significantly less severe than the damage caused by the field isolates. The active immune response induced by vaccination was cross-protective against the pathological effects produced by the different isolates used in this study.     

马立克氏病病毒感染鸡对新城疫疫苗和法氏囊疫苗免疫反应的影响

研究了马立克氏病病毒(MDV)不同致病型毒株感染鸡后对新城疫病毒(NDV)和传染性法氏囊病病毒(IBDV)疫苗抗体反应的影响。结果表明，2周龄接种MDV超强毒株RBIB和7日龄接种MDV强毒株GA的鸡HI效价均显著低于对照鸡，但在本试验条件下尚未发现MDV感染对法氏囊病病毒疫苗免疫效果有显著影响。     

Field trial in commercial broilers with a multivalent in ovo vaccine comprising a mixture of live viral vaccines against Marek's disease,infectious bursal disease,Newcastle disease,and fowl pox

A multivalent in ovo vaccine (MIV) was tested for safety and efficacy in a commercial broiler complex. The MIV comprised five replicating live viruses including serotypes 1, 2, and 3 of Marek's disease virus (MDV), an intermediate infectious bursal disease virus (IBDV) and a recombinant fowl poxvirus (FPV) vector vaccine containing HN and F genes of Newcastle disease virus (NDV). The performance of MIV-vaccinated broilers was compared with that of hatchmates that received turkey herpesvirus (HVT) alone (routinely used in ovo vaccine in the broiler complex). The chickens that hatched from the MIV-injected and HVT-injected eggs were raised under commercial conditions in six barns. Barn 1 housed 17,853 MIV-vaccinated chickens and each of the barns 2-6 housed 18,472-22,798 HVT-vaccinated chickens. The HVT-vaccinated chickens were given infectious bronchitis virus (IBV) and NDV vaccines at hatch and at 2 wk of age. The MIV-vaccinated chickens received IBV vaccine at hatch and IBV + NDV at 2 wk of age. The relative values of hatchability of eggs, livability and weight gain of chickens, and condemnation rates at processing were comparable between the MIV and the HVT groups (P > 0.05). Chickens from the MIV- and the HVT-vaccinated groups were challenged with virulent viruses under laboratory conditions. The resistance of vaccinated chickens against Marek's disease could not be assessed because of high natural resistance of unvaccinated commercial broilers to virulent MDV. The relative resistances of the MIV- and the HVT-vaccinated groups, respectively, against other virulent viruses were as follows: IBDV, 100% for both groups; NDV, 81% vs. 19%; FPV, 86% vs. 0%. The successful use of MIV under field conditions expands the usefulness of the in ovo technology for poultry.     

传染性囊病病毒诱导细胞凋亡的初步观察

用１株ＩＢＤＶ强毒株感染易感小鸡，对病鸡法氏囊进行电镜观察及ＤＮＡ电泳分析，直接观察到病鸡法氏囊中Ｂ淋巴细胞凋亡的典型形态学特征和生化变化：染色质凝聚成团，集于核膜旁，胞膜与核膜出现凹陷，细胞拉长变形，最后细胞裂解成由膜包围着的小团，被网状细胞和巨噬细胞吞噬；感染ＩＢＤＶ２４～４８ｈ的法氏囊细胞总ＤＮＡ在电泳谱上呈梯状条带，而从正常的法氏囊提取的总ＤＮＡ在电泳谱上只有１条带。结果表明，ＩＢＤＶ感染小鸡之后，导致了法氏囊中Ｂ淋巴细胞的凋亡。作者据此推断，细胞凋亡是造成Ｂ淋巴细胞数量减少，从而导致小鸡免疫抑制的原因     

Responses of specific-pathogen-free chicks to concomitant infections of reovirus (WVU-2937) and infectious bursal disease virus

Specific-pathogen-free white leghorn chicks concomitantly infected with both infectious bursal disease virus (IBDV) and reovirus (WVU-2937) on day 1 had significantly lower (P less than 0.05) virus-neutralizing- and precipitating-antibody geometric mean titers (GMT) to reovirus than chicks infected with only reovirus on day 1 but had a similar incidence of inflammation of the metatarsal digital flexor tendons. Chicks infected with IBDV on day 7 and reovirus on day 14 had a greater incidence of inflammation of the tarsometatarsal digital flexor tendons and lower neutralizing- and precipitating-antibody GMT to reovirus than chicks infected with only reovirus on day 14. Chicks infected with both viruses on day 1 had a significantly lower (P less than 0.05) neutralizing-antibody GMT to IBDV than chicks infected with only IBDV.