School of Veterinary Science, The University of Melbourne, Parkville, Victoria 3010, Australia.
Vaccine. 2011 Dec 6;29(52):9583-7. doi: 10.1016/j.vaccine.2011.10.055. Epub 2011 Oct 30.
Infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus that causes acute respiratory disease in poultry. Live attenuated ILTV vaccines have been used extensively to help control outbreaks of disease. Two Australian-origin attenuated vaccine strains, SA2 and A20 ILTV, are commercially available and are in frequent use in Australia. Both these vaccines are of chicken embryo origin (CEO). The A20 ILTV strain was developed from the SA2 ILTV strain by sequential passage of SA2 ILTV in tissue culture in order to reduce its residual virulence. Previous studies in our laboratories have demonstrated the greater attenuation of A20 ILTV under controlled experimental conditions, but the genetic basis of the in vivo phenotypes of A20 and SA2 ILTV has not been elucidated. In this study, the genetic differences between A20 and SA2 ILTV were examined by performing complete genome sequencing and comparative analysis. The genome sequences were also compared to a reference sequence from another CEO ILTV vaccine (Serva ILTV: GenBank accession number HQ_630064) of European-origin. Additional in ovo studies to assess cell to cell spread were performed in order to allow further comparisons of the pathogenicity of SA2 and A20 ILTV. The sequencing results showed that the genome sizes of SA2 and A20 ILTV were 152,975 and 152,978bp, respectively, while Serva ILTV had a genome size of 152,630bp. The genomes of SA2 and A20 ILTV shared 99.9% nucleotide sequence identity with each other, but only 99.2% identity with Serva ILTV. In complete genome alignments between SA2 and A20 ILTV, a total of 24 single nucleotide polymorphisms (SNPs) were identified, but only two of these were non-synonymous. These were located in the ORF B and UL15 genes. Four indels were detected in non-coding regions. The findings from this study demonstrate the general genetic stability of ILTV, but also show that non-synonymous changes in the ORF B and UL15 genes have arisen following tissue culture passage of SA2 ILTV to produce the A20 vaccine. It is likely that these non-synonymous changes are related to the greater attenuation of A20 ILTV compared to SA2 ILTV, and to the reduced ability of A20 ILTV to spread from cell to cell, as observed in this study. The results from this study also demonstrate the divergence between the genomes of the Australian-origin ILTV vaccine strains and the Serva vaccine strain.
传染性喉气管炎病毒（ILTV）是一种α疱疹病毒，可导致家禽急性呼吸道疾病。已广泛使用活减毒 ILTV 疫苗来帮助控制疾病爆发。两种澳大利亚起源的减毒疫苗株，SA2 和 A20 ILTV，在澳大利亚商业上可用且经常使用。这两种疫苗均源自鸡胚（CEO）。A20 ILTV 株是通过在组织培养中连续传代 SA2 ILTV 从 SA2 ILTV 株开发而来，以降低其残余毒力。我们实验室之前的研究表明，A20 在受控实验条件下的衰减程度更大，但 A20 和 SA2 ILTV 的体内表型的遗传基础尚未阐明。在这项研究中，通过进行全基因组测序和比较分析来检查 A20 和 SA2 ILTV 之间的遗传差异。还将基因组序列与来自欧洲起源的另一种 CEO ILTV 疫苗（Serva ILTV：GenBank 登录号 HQ_630064）的参考序列进行比较。进行了额外的鸡胚研究以评估细胞间传播，以便进一步比较 SA2 和 A20 ILTV 的致病性。测序结果表明，SA2 和 A20 ILTV 的基因组大小分别为 152,975 和 152,978bp，而 Serva ILTV 的基因组大小为 152,630bp。SA2 和 A20 ILTV 的基因组彼此之间共享 99.9%的核苷酸序列同一性，但与 Serva ILTV 仅具有 99.2%的同一性。在 SA2 和 A20 ILTV 之间的全基因组比对中，共鉴定出 24 个单核苷酸多态性（SNP），但其中只有两个是非同义的。这些位于 ORF B 和 UL15 基因中。在非编码区检测到 4 个插入缺失。本研究的结果表明 ILTV 的一般遗传稳定性，但也表明 SA2 ILTV 经组织培养传代产生 A20 疫苗后，ORF B 和 UL15 基因中的非同义变化已经出现。这些非同义变化很可能与 A20 ILTV 相对于 SA2 ILTV 的衰减更大以及 A20 ILTV 从细胞到细胞的传播能力降低有关，正如本研究中观察到的那样。本研究的结果还表明，澳大利亚起源的 ILTV 疫苗株和 Serva 疫苗株之间的基因组存在差异。
