Key Laboratory of Animal Immunology, Ministry of Agriculture and Rural Affairs of China & Henan Provincial Key Laboratory of Animal Immunology, Henan Academy of Agricultural Sciences, Zhengzhou 450002, China.
UK-China Centre of Excellence for Research on Avian Diseases, Henan Academy of Agricultural Sciences, Zhengzhou 450002, China.
Viruses. 2022 Jul 27;14(8):1651. doi: 10.3390/v14081651.
In recent years, outbreaks of Marek's disease (MD) have been frequently reported in vaccinated chicken flocks in China. Herein, we have demonstrated that four Marek's disease virus (MDV) isolates, HN502, HN302, HN304, and HN101, are all pathogenic and oncogenic to hosts. Outstandingly, the HN302 strain induced 100% MD incidence, 54.84% mortality, and 87.10% tumor incidence, together with extensive atrophy of immune organs. Pathotyping of HN302 was performed in comparison to a standard very virulent (vv) MDV strain Md5. We found that both CVI988 and HVT vaccines significantly reduced morbidity and mortality induced by HN302 or Md5 strains, but the protection indices (PIs) provided by these two vaccines against HN302 were significantly lower (27.03%) or lower (33.33%) than that against Md5, which showed PIs of 59.89% and 54.29%, respectively. These data suggested that HN302 possesses a significant higher virulence than Md5 and at least could be designated as a vvMDV strain. Together with our previous phylogenetic analysis on MDV-1 meq genes, we have presently suggested HN302 to be a typical highly virulent MDV variant belonging to an independent Chinese branch. To our knowledge, this is the first report to provide convincible evidence to identify a pathogenic MDV variant strain with a higher virulence than Md5 in China, which may have emerged and circulating in poultry farms in China for a long time and involved in the recent MD outbreaks.
近年来，中国接种疫苗的鸡群中频繁报告马立克氏病（MD）暴发。在此，我们证明了 4 株马立克氏病病毒（MDV）分离株 HN502、HN302、HN304 和 HN101 对宿主均具有致病性和致癌性。值得注意的是，HN302 株引起了 100%的 MD 发病率、54.84%的死亡率和 87.10%的肿瘤发病率，同时免疫器官广泛萎缩。与标准超强毒（vv）MDV 株 Md5 相比，对 HN302 进行了病理分型。我们发现 CVI988 和 HVT 疫苗均显著降低了 HN302 或 Md5 株引起的发病率和死亡率，但这两种疫苗对 HN302 的保护指数（PI）明显较低（27.03%）或更低（33.33%），而对 Md5 的保护指数分别为 59.89%和 54.29%。这些数据表明，HN302 的毒力明显高于 Md5，至少可以被指定为 vvMDV 株。结合我们之前对 MDV-1 meq 基因的系统进化分析，我们目前认为 HN302 是一种典型的高致病性 MDV 变异株，属于一个独立的中国分支。据我们所知，这是首次报道在中国发现一种致病性 MDV 变异株，其毒力高于 Md5，可能在中国的家禽养殖场中已经长期出现和传播，并参与了最近的 MD 暴发。
