College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, Sichuan, People's Republic of China.
Virol J. 2011 Mar 15;8:121. doi: 10.1186/1743-422X-8-121.
Marek's disease (MD) is an economically important viral disease of chickens caused by Marek's disease virus (MDV), an oncogenic herpesvirus. This disease was well controlled since the widespread use of commercial vaccines, but field MDVs have shown continuous increasing in virulence and acquired the ability to overcome the immune response induced by vaccines. Nowadays, MD continues to be a serious threat to poultry industry, isolation and characterization of MDVs are essential for monitoring changes of viruses and evaluating the effectiveness of existing vaccines.
Between 2008 and 2010, 18 field MDV strains were isolated from vaccinated chicken flocks in Sichuan province, China. Three oncogenic genes including Meq, pp38 and vIL-8 genes of the 18 isolates were amplified and sequenced. Homology analysis showed that the deduced amino acid sequences of these three genes exhibit 95.0-98.8%, 99.3-100% and 97.0-98.5% homology respectively with these of other reference strains published in GenBank. Alignment analysis of the nucleotide and deduced amino acid sequences showed that four amino acid mutations in Meq gene and two amino acid mutations in vIL-8 gene displayed perfect regularity in MDVs circulating in China, which could be considered as features of field MDVs prevalent in recent years in China. In addition, one amino acid mutation in pp38 gene can be considered as a feature of virulent MDVs from USA, and three amino acid mutations in Meq gene were identified and unique in very virulent plus (vv+) MDVs. Phylogenetic analysis based on Meq and vIL-8 protein sequences revealed that field MDVs in China evolved independently. Virulence studies showed that CVI988 could provide efficient protection against the field MDVs epidemic recently in China.
This study and other published data in the GenBank have demonstrated the features of Meq, pp38 and vIL-8 genes of MDVs circulating in recent years in Sichuan, China. Mutations, deletions or insertions were observed in these three genes, and some mutations could be considered as the unique marks of the MDVs circulating presently in China. The paper supplies some valuable information concerning the evolution of MDV which is useful for the vaccine development and control of MD in China.
马立克氏病（MD）是一种由马立克氏病病毒（MDV）引起的鸡的重要经济病毒性疾病，MDV 是一种致癌疱疹病毒。自从广泛使用商业疫苗以来，这种疾病得到了很好的控制，但田间 MDV 不断显示出毒力的持续增加，并获得了克服疫苗诱导的免疫反应的能力。如今，MD 继续对家禽业构成严重威胁，因此分离和鉴定 MDV 对于监测病毒的变化和评估现有疫苗的有效性至关重要。
2008 年至 2010 年，从中国四川省接种鸡群中分离到 18 株田间 MDV。扩增并测序了这 18 个分离株的三个致癌基因，包括 Meq、pp38 和 vIL-8 基因。同源性分析表明，这些三个基因的推导氨基酸序列与 GenBank 中发表的其他参考株分别具有 95.0-98.8%、99.3-100%和 97.0-98.5%的同源性。核苷酸和推导氨基酸序列的比对分析表明，Meq 基因中的四个氨基酸突变和 vIL-8 基因中的两个氨基酸突变在我国流行的 MDV 中具有完全的规律性，这可以被认为是近年来我国流行的田间 MDV 的特征。此外，pp38 基因中的一个氨基酸突变可以被认为是美国毒力 MDV 的特征，在非常毒力加（vv+）MDV 中鉴定到三个 Meq 基因中的氨基酸突变，且这些突变是独特的。基于 Meq 和 vIL-8 蛋白序列的系统进化分析表明，中国的田间 MDV 是独立进化的。毒力研究表明，CVI988 可以为中国最近流行的田间 MDV 提供有效的保护。
本研究和 GenBank 中发表的其他数据表明，四川近年来流行的 MDV 的 Meq、pp38 和 vIL-8 基因具有特征。在这三个基因中观察到突变、缺失或插入，一些突变可以被认为是目前在中国流行的 MDV 的独特标记。该论文提供了有关 MDV 进化的一些有价值的信息，这对于中国的 MD 疫苗开发和控制很有用。
