Marek's disease (MD) is a highly contagious lymphoproliferative disease of chickens caused by Gallid alphaherpesvirus 2, commonly known as serotype 1 Marek's disease virus (MDV-1). Despite widespread vaccination, MD-related cases have been frequently observed worldwide, including in Thailand. However, no information is available on the genetic characteristics of MDV-1 field strains circulating in chickens in Thailand. This study investigated the geographic distribution and genetic characteristics of MDV-1 field strains circulating in chickens in Thailand between 2013 and 2021 by analysing the Meq and pp38 genes. Out of a total of the 286 clinical samples obtained from 70 chicken farms located in major chicken raising areas of Thailand, 138 samples (48.25%) from 46 chicken farms (65.71%) tested positive for MDV-1 field strains. Results demonstrated that MDV-1 field strains were extensively distributed in major chicken raising areas. Phylogenetic analyses based on the Meq gene revealed that four clusters of MDV-1 circulated in chickens in Thailand between 2013 and 2021. Among these clusters, cluster 1 was the predominant cluster circulating in chickens in Thailand. Additionally, our findings based on molecular characteristics of Meq and pp38 gene/protein suggested that most of the Thai MDV-1 field strains were potentially highly virulent. In conclusion, our data demonstrated the circulation of different clusters of MDV-1 with virulence characteristics in chickens in Thailand, indicating high genetic diversity of MDV-1 in Thailand. This study highlights the importance of more effective vaccine development and routine MDV-1 surveillance for early detection and control of highly virulent MDV-1.

中文翻译：

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泰国鸡马立克氏病病毒的遗传特征揭示了流行株的高度遗传多样性

马立克氏病 (MD) 是由鸡alphaherpesvirus 2引起的高度传染性鸡淋巴组织增生性疾病，通常称为血清型 1 马立克氏病病毒 (MDV-1)。尽管广泛接种疫苗，但在世界范围内经常观察到与 MD 相关的病例，包括在泰国。然而，没有关于在泰国鸡群中传播的 MDV-1 野毒株的遗传特征的信息。本研究通过分析Meq和pp38，调查了 2013 年至 2021 年间在泰国鸡群中流行的 MDV-1 野毒株的地理分布和遗传特征基因。从泰国主要养鸡区的70家养鸡场采集的286份临床样本中，46家（65.71%）养鸡场的138份（48.25%）MDV-1野毒检测呈阳性。结果表明MDV-1野毒株广泛分布于主要养鸡区。基于Meq的系统发育分析基因显示，2013 年至 2021 年期间，四个 MDV-1 簇在泰国的鸡群中传播。在这些簇群中，簇群 1 是在泰国鸡群中传播的主要簇群。此外，我们基于 Meq 和 pp38 基因/蛋白质的分子特征的研究结果表明，大多数泰国 MDV-1 野毒株具有潜在的高毒力。总之，我们的数据显示了泰国鸡群中具有毒力特征的不同 MDV-1 簇的传播，表明泰国 MDV-1 的遗传多样性很高。这项研究强调了更有效的疫苗开发和常规 MDV-1 监测对于早期检测和控制高毒性 MDV-1 的重要性。