Poultry Diagnostic and Research Center, Department of Population Health, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602, USA.
Southeast Poultry Research Laboratory, US National Poultry Research Center, ARS, USDA, Athens, GA 30605, USA.
Vaccine. 2018 Oct 1;36(41):6077-6086. doi: 10.1016/j.vaccine.2018.08.078. Epub 2018 Sep 7.
Almost all commercial poultry are vaccinated against avian coronavirus infectious bronchitis virus (IBV) using live attenuated vaccines mass administered by spray at day of hatch. Although many different types of IBV vaccines are used successfully, the ArkDPI serotype vaccine, when applied by spray, does not infect and replicate sufficiently to provide protection against homologous challenge. In this study, we examined a different Ark vaccine strain (Ark99), which is no longer used commercially due to its reactivity in one day old chicks, to determine if it could be further attenuated by passage in embryonated eggs but still provide adequate protection. Further attenuation of the Ark99 vaccine was achieved by passage in embryonated eggs but ArkGA P1, P20, and P40 (designated ArkGA after P1) were still too reactive to be suitable vaccine candidates. However, ArkGA P60 when given by spray had little or no vaccine reaction in one day old broiler chicks, and it induced protection from clinical signs and ciliostasis following homologous challenge. In addition, vaccinated and challenged birds had significantly less challenge virus, an important measure of protection, compared to non-vaccinated and challenged controls. The full-length genomes of viruses from egg passages 1, 20, 40, and 60 were sequenced using the Illumina platform and the data showed single nucleotide polymorphisms (SNPs) had accumulated in regions of the genome associated with viral replication, pathogenicity, and cell tropism. ArkGA P60 accumulated the most SNPs in key genes associated with pathogenicity (polyprotein gene 1ab) and cell tropism (spike gene), compared to previous passages, which likely resulted in its more attenuated phenotype. These results indicate that the ArkGA P60 vaccine is safe for spray vaccination of broiler chicks and induces suitable protection against challenge with pathogenic Ark-type virus.
几乎所有商业家禽都使用活减毒疫苗通过喷雾在孵化日接种来预防禽冠状病毒传染性支气管炎病毒（IBV）。虽然使用了许多不同类型的 IBV 疫苗，但当通过喷雾应用 ArkDPI 血清型疫苗时，它不能充分感染和复制以提供针对同源性挑战的保护。在这项研究中，我们检查了另一种 Ark 疫苗株（Ark99），由于其在 1 日龄雏鸡中的反应性，该疫苗株已不再商业使用，以确定它是否可以通过在鸡胚中传代进一步减毒，但仍能提供足够的保护。通过在鸡胚中传代进一步减毒了 Ark99 疫苗，但 ArkGA P1、P20 和 P40（P1 后命名为 ArkGA）仍然过于活跃，不适合作为候选疫苗。然而，当通过喷雾给予 ArkGA P60 时，1 日龄肉鸡雏鸡的疫苗反应很小或没有，并且它诱导了对同源性挑战的临床症状和纤毛静止的保护。此外，与未接种和挑战的对照相比，接种和挑战的鸟类的挑战病毒明显减少，这是保护的一个重要衡量标准。使用 Illumina 平台对来自鸡蛋传代 1、20、40 和 60 的病毒全长基因组进行测序，数据显示单核苷酸多态性（SNP）在与病毒复制、致病性和细胞嗜性相关的基因组区域积累。与之前的传代相比，ArkGA P60 在与致病性（多蛋白基因 1ab）和细胞嗜性（刺突基因）相关的关键基因中积累了最多的 SNP，这可能导致其更减毒的表型。这些结果表明，ArkGA P60 疫苗可安全用于肉鸡雏鸡的喷雾接种，并诱导对致病性 Ark 型病毒的挑战产生适当的保护。
