Arzt Jonathan, Pacheco Juan M, Stenfeldt Carolina, Rodriguez Luis L
Foreign Animal Disease Research Unit, Plum Island Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, Greenport, NY, USA.
Oak Ridge Institute for Science and Education, PIADC Research Participation Program, Oak Ridge, TN, USA.
Virol J. 2017 May 2;14(1):89. doi: 10.1186/s12985-017-0758-9.
Understanding the mechanisms of attenuation and virulence of foot-and-mouth disease virus (FMDV) in the natural host species is critical for development of next-generation countermeasures such as live-attenuated vaccines. Functional genomics analyses of FMDV have identified few virulence factors of which the leader proteinase (L) is the most thoroughly investigated. Previous work from our laboratory has characterized host factors in cattle inoculated with virulent FMDV and attenuated mutant strains with transposon insertions within L.
In the current study, the characteristics defining virulence of FMDV in cattle were further investigated by comparing the pathogenesis of a mutant, attenuated strain (FMDV-Mut) to the parental, virulent virus from which the mutant was derived (FMDV-WT). The only difference between the two viruses was an insertion mutation in the inter-AUG region of the leader proteinase of FMDV-Mut. All cattle were infected by simulated-natural, aerosol inoculation.
Both viruses were demonstrated to establish primary infection in the nasopharyngeal mucosa with subsequent dissemination to the lungs. Immunomicroscopic localization of FMDV antigens indicated that both viruses infected superficial epithelial cells of the nasopharynx and lungs. The critical differences between the two viruses were a more rapid establishment of infection by FMDV-WT and quantitatively greater virus loads in secretions and infected tissues compared to FMDV-Mut. The slower replicating FMDV-Mut established a subclinical infection that was limited to respiratory epithelial sites, whereas the faster replication of FMDV-WT facilitated establishment of viremia, systemic dissemination of infection, and clinical disease.
The mutant FMDV was capable of achieving all the same early pathogenesis landmarks as FMDV-WT, but was unable to establish systemic infection. The precise mechanism of attenuation remains undetermined; but current data suggests that the impaired replication of the mutant is more responsible for attenuation than differences in host immunological factors. These results complement previous studies by providing data of high-granularity describing tissue-specific tropism of FMDV and by demonstrating microscopic localization of virulent and attenuated clones of the same field-strain FMDV.
了解口蹄疫病毒（FMDV）在天然宿主物种中的减毒和毒力机制对于开发下一代对策（如减毒活疫苗）至关重要。FMDV的功能基因组学分析已鉴定出少数毒力因子，其中前导蛋白酶（L）是研究最深入的。我们实验室先前的工作已对接种强毒FMDV和L内有转座子插入的减毒突变株的牛中的宿主因子进行了表征。
在当前研究中，通过比较突变减毒株（FMDV-Mut）与衍生出该突变株的亲本强毒病毒（FMDV-WT）的发病机制，进一步研究了FMDV在牛中毒力的定义特征。两种病毒之间的唯一差异是FMDV-Mut前导蛋白酶的AUG间区域存在插入突变。所有牛均通过模拟自然气溶胶接种进行感染。
两种病毒均被证明在鼻咽黏膜中建立原发性感染，随后传播至肺部。FMDV抗原的免疫显微镜定位表明，两种病毒均感染鼻咽和肺部的浅表上皮细胞。两种病毒之间的关键差异在于，与FMDV-Mut相比，FMDV-WT感染建立得更快，分泌物和感染组织中的病毒载量在数量上更高。复制较慢的FMDV-Mut建立了限于呼吸道上皮部位的亚临床感染，而FMDV-WT更快的复制促进了病毒血症的建立、感染的全身传播和临床疾病。
突变型FMDV能够实现与FMDV-WT相同的所有早期发病标志，但无法建立全身感染。减毒的确切机制仍未确定；但目前的数据表明，突变体复制受损比宿主免疫因素的差异更易导致减毒。这些结果通过提供描述FMDV组织特异性嗜性的高分辨率数据以及证明同一田间毒株FMDV的强毒株和减毒株的显微镜定位，补充了先前的研究。
