Spackman Erica, Stephens Christopher B, Pantin-Jackwood Mary J
Southeast Poultry Research Laboratory, United States National Poultry Research Center, United States Department of Agriculture, Agricultural Research Service, 934 College Station Rd., Athens, GA 30605.
Avian Dis. 2018 Mar;62(1):36-44. doi: 10.1637/11769-110717-Reg.1.
Poor efficacy of avian influenza virus (AIV) vaccines in chickens has been documented in the field in spite of good results in experimental settings. Although the causes are multifactorial and complex, one contributing factor may be prior infection with immunosuppressive viruses. In an effort to evaluate the role of immunosuppressive agents on AIV pathogenesis and vaccine efficacy, the effect of prior infection with infectious bursal disease virus (IBDV), a ubiquitous immunosuppressive virus of chickens, was evaluated. Specific-pathogen-free white Plymouth Rock chickens were exposed to variant E IBDV at 1 day of age and were subsequently vaccinated with an inactivated H7 AIV vaccine 2 wk later. Vaccinated chickens exposed to IBDV had a geometric mean antibody titer to AIV of 1:1.7 by hemagglutination inhibition assay compared to a geometric mean titer of 1:47.5 from chickens that were vaccinated but not exposed to IBDV. Three weeks postvaccination, the chickens were challenged with one of six different doses of highly pathogenic (HP) AIV homologous to the vaccine. Within challenge virus dose groups, vaccinated chickens exposed to IBDV had similar mortality rates to nonvaccinated chickens that were not exposed to IBDV. In contrast, vaccinated chickens that were not exposed to IBDV were protected from mortality. Exposure to IBDV also decreased the mean death time (2.3-3.7 days depending on dose) compared with vaccinated birds not exposed to IBDV (4-7 days depending on dose). Neither vaccination nor IBDV infection had an effect on mean bird infection dose with HPAIV, but the 50% bird lethal dose was reduced from >10 50% egg infective dose (EID) in the vaccinated, IBDV-nonexposed group to 10 EID in the vaccinated group exposed to IBDV. These results are consistent with IBDV exposure contributing to poor vaccine efficacy in the field.
尽管禽流感病毒（AIV）疫苗在实验环境中取得了良好效果，但在实际养殖中，鸡群接种该疫苗后的效果却不佳。虽然造成这种情况的原因是多方面且复杂的，但一个促成因素可能是先前感染了免疫抑制性病毒。为了评估免疫抑制剂对AIV发病机制和疫苗效果的作用，研究人员评估了鸡传染性法氏囊病病毒（IBDV）这一普遍存在的鸡免疫抑制性病毒的先前感染影响。将无特定病原体的白普利茅斯岩鸡在1日龄时暴露于IBDV变异E型，随后在2周后接种灭活H7 AIV疫苗。通过血凝抑制试验，暴露于IBDV的接种鸡对AIV的几何平均抗体效价为1:1.7，而未暴露于IBDV的接种鸡的几何平均效价为1:47.5。疫苗接种后三周，用与疫苗同源的六种不同剂量的高致病性（HP）AIV之一对鸡进行攻毒。在攻毒病毒剂量组内，暴露于IBDV的接种鸡的死亡率与未暴露于IBDV的未接种鸡相似。相比之下，未暴露于IBDV的接种鸡则受到保护，未出现死亡。与未暴露于IBDV的接种鸡（根据剂量不同，死亡时间为4 - 7天）相比，暴露于IBDV也缩短了平均死亡时间（根据剂量不同，为2.3 - 3.7天）。接种疫苗和IBDV感染对高致病性禽流感病毒的平均禽感染剂量均无影响，但50%禽致死剂量从未暴露于IBDV的接种组中的>10⁵⁰%鸡胚感染剂量（EID）降至暴露于IBDV的接种组中的10 EID。这些结果表明，在实际养殖中，暴露于IBDV会导致疫苗效果不佳。
