Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin, People's Republic of China.
J Virol. 2022 May 25;96(10):e0024122. doi: 10.1128/jvi.00241-22. Epub 2022 May 5.
In this study, 232 class I Newcastle disease viruses (NDVs) were identified from multiple bird species at nationwide live bird markets (LBMs) from 2017 to 2019 in China. Phylogenetic analysis indicated that all 232 isolates were clustered into genotype 1.1.2 of class I on the basis of the fusion (F) gene sequences, which were distinct from the genotypes identified in other countries. Most of the isolates (212/232) were shown to have the typical F gene molecular characteristics of class I NDVs, while a few (20/232) contained mutations at the site of the conventional start codon of the F gene, which resulted in open reading frames (ORFs) altered in length. The isolates with ACG, CTA, and ATA mutations showed different levels of increased virulence and replication capacity, suggesting that these viruses may be transitional types during the evolution of class I NDVs from avirulent to virulent. Further evaluation of biological characteristics with recombinant viruses obtained by reverse genetics demonstrated that the ATG located at genomic positions 4523 to 4525 was the authentic start codon in the F gene of class I NDV, and the specific ATA mutations which contributed to the expression of F protein on the surface of infected cells were the key determinants of increased replication capacity and virulence. Interestingly, the mutation at the corresponding site of genotype II LaSota of class II had no effects on the virulence and replication capacity in chickens. Our results suggest that the alteration of virulence and replication capacity caused by specific mutations in the F gene could be a specific characteristic of class I NDVs and indicate the possibility of the emergence of virulent NDVs due to the persistent circulation of class I NDVs. The available information on the distribution, genetic diversity, evolution, and biological characteristics of class I Newcastle disease viruses (NDVs) in domestic poultry is currently very limited. Here, identification of class I NDVs at nationwide live bird markets (LBMs) in China was performed and representative isolates were characterized. A widespread distribution of genotype 1.1.2 of class I NDVs was found in multiple bird species at LBMs in China. Though most isolates demonstrated typical molecular characteristics of class I NDVs, a few that contained specific mutations at the site of the conventional start codon of the fusion gene with increased virulence and replication capacity were identified for the first time. Our findings indicate that the virulence of class I NDVs could have evolved, and the widespread transmission and circulation of class I NDVs may represent a potential threat for disease outbreaks in poultry.
在这项研究中，我们从 2017 年至 2019 年在中国全国活禽市场（LBM）的多种鸟类中鉴定出 232 株 I 型新城疫病毒（NDV）。系统进化分析表明，基于融合（F）基因序列，所有 232 个分离株均聚集为 I 型的 1.1.2 基因型，与其他国家鉴定的基因型明显不同。大多数分离株（212/232）具有 I 型 NDV 的典型 F 基因分子特征，而少数（20/232）在 F 基因常规起始密码子位点存在突变，导致 ORF 长度改变。具有 ACG、CTA 和 ATA 突变的分离株显示出不同程度的增加毒力和复制能力，表明这些病毒可能是 I 型 NDV 从无毒向有毒进化过程中的过渡类型。使用反向遗传学获得的重组病毒进一步评估生物学特性表明，位于基因组位置 4523 到 4525 的 ATG 是 I 型 NDV F 基因中的真实起始密码子，并且导致感染细胞表面 F 蛋白表达的特定 ATA 突变是增加复制能力和毒力的关键决定因素。有趣的是，II 型 LaSota 的对应位点的突变对鸡的毒力和复制能力没有影响。我们的结果表明，F 基因特定突变引起的毒力和复制能力的改变可能是 I 型 NDV 的一个特定特征，并表明由于 I 型 NDV 的持续循环，可能会出现毒力更强的 NDV。目前，关于家禽中 I 型新城疫病毒（NDV）的分布、遗传多样性、进化和生物学特性的信息非常有限。在这里，我们对中国全国活禽市场（LBM）中的 I 型 NDV 进行了鉴定，并对代表性分离株进行了特征描述。我们发现，在中国的 LBM 中，多种鸟类中广泛分布着 I 型 1.1.2 基因型的 NDV。尽管大多数分离株表现出 I 型 NDV 的典型分子特征，但我们首次发现了一些具有融合基因常规起始密码子位点特定突变的分离株，这些突变株具有增加的毒力和复制能力。我们的研究结果表明，I 型 NDV 的毒力可能已经进化，I 型 NDV 的广泛传播和循环可能对家禽疾病爆发构成潜在威胁。
