Rautenschlein S, Kraemer Ch, Vanmarcke J, Montiel E
Clinic for poultry, Veterinary School Hannover, Bünteweg 17, 30559 Hannover, Germany.
Avian Dis. 2005 Jun;49(2):231-7. doi: 10.1637/7310-112204R.
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.
超强毒力（vv）传染性法氏囊病病毒（IBDV）的进化已在许多家禽养殖地区造成了重大经济损失。尽管采取了积极的疫苗接种策略，但IBDV仍难以控制。传统上，IBDV疫苗的保护效力是在无特定病原体（SPF）鸡中评估的。但在田间条件下，母源抗体（mAb）残留水平可能会干扰疫苗效力。在本研究中，用不同毒力的IBDV疫苗（疫苗1 - 3，中等毒力；疫苗4，中等偏上毒力）对具有不同母源抗体水平的商品肉鸡进行接种。在接种日母源病毒中和抗体（mAb）平均水平为log2 10.8（范围7.6 - 11.6）时，只有中等偏上毒力疫苗在18天后诱导产生了IBDV抗体，而其他中等毒力疫苗则未诱导产生。在接种日mAb平均水平为log2 6.7（范围5.6 - 8.6）时，所有疫苗均诱导产生了循环抗体，尽管不同毒株之间抗体产生的起始时间差异显著（P < 0.05）。中等偏上毒力疫苗在接种后14天就诱导产生了酶联免疫吸附测定抗体水平，而中等毒力疫苗在接种后28天（疫苗1、2）和35天（疫苗3）诱导产生了显著的抗体水平。IBDV抗体诱导时间与法氏囊病变的起始相关。疫苗1、3和4之间的病变严重程度相当（病变评分4），而疫苗2在23%的受试鸡中仅诱导出评分为1的轻度病变。尽管诱导产生了抗体，但所测试的疫苗均未完全保护鸡只免受vvIBDV攻击。与未受攻击的鸡相比，所有受攻击的鸡要么法氏囊病变评分显著更高，要么法氏囊中IBDV抗原载量更高，有时两者都高（P < 0.05）。我们的研究表明，在商品肉鸡中评估IBDV疫苗效力很困难。首次表明，与SPF鸡相比，在存在mAb的情况下，接种IBDV疫苗的肉鸡法氏囊病变的起始和恢复会延迟，但并不像之前所认为的那样受到抑制。在攻击时，接种疫苗的鸡可能仍有明显的法氏囊病变，并且可能缺乏IBDV攻击病毒的靶细胞。为了能够在商品肉鸡中评估疫苗效力，除了法氏囊病变评分外，还应结合法氏囊内IBDV抗原载量等参数进行考虑。
