Goodman Laura B, Loregian Arianna, Perkins Gillian A, Nugent Josie, Buckles Elizabeth L, Mercorelli Beatrice, Kydd Julia H, Palù Giorgio, Smith Ken C, Osterrieder Nikolaus, Davis-Poynter Nicholas
Department of Microbiology and Immunology, Cornell University, Ithaca, New York, United States of America.
PLoS Pathog. 2007 Nov;3(11):e160. doi: 10.1371/journal.ppat.0030160.
Infection with equid herpesvirus type 1 (EHV-1) leads to respiratory disease, abortion, and neurologic disorders in horses. Molecular epidemiology studies have demonstrated that a single nucleotide polymorphism resulting in an amino acid variation of the EHV-1 DNA polymerase (N752/D752) is significantly associated with the neuropathogenic potential of naturally occurring strains. To test the hypothesis that this single amino acid exchange by itself influences neuropathogenicity, we generated recombinant viruses with differing polymerase sequences. Here we show that the N752 mutant virus caused no neurologic signs in the natural host, while the D752 virus was able to cause inflammation of the central nervous system and ataxia. Neurologic disease induced by the D752 virus was concomitant with significantly increased levels of viremia (p = 0.01), but the magnitude of virus shedding from the nasal mucosa was similar between the N752 and D752 viruses. Both viruses replicated with similar kinetics in fibroblasts and epithelial cells, but exhibited differences in leukocyte tropism. Last, we observed a significant increase (p < 0.001) in sensitivity of the N752 mutant to aphidicolin, a drug targeting the viral polymerase. Our results demonstrate that a single amino acid variation in a herpesvirus enzyme can influence neuropathogenic potential without having a major effect on virus shedding from infected animals, which is important for horizontal spread in a population. This observation is very interesting from an evolutionary standpoint and is consistent with data indicating that the N752 DNA pol genotype is predominant in the EHV-1 population, suggesting that decreased viral pathogenicity in the natural host might not be at the expense of less efficient inter-individual transmission.
1型马疱疹病毒（EHV-1）感染可导致马匹出现呼吸道疾病、流产和神经紊乱。分子流行病学研究表明，EHV-1 DNA聚合酶的一个单核苷酸多态性导致氨基酸变异（N752/D752）与自然发生毒株的神经致病潜力显著相关。为了验证这一单氨基酸交换本身会影响神经致病性的假说，我们构建了具有不同聚合酶序列的重组病毒。在此我们表明，N752突变病毒在天然宿主中未引起神经症状，而D752病毒能够引起中枢神经系统炎症和共济失调。D752病毒诱导的神经疾病与病毒血症水平显著升高相关（p = 0.01），但N752和D752病毒从鼻黏膜的病毒排出量相似。两种病毒在成纤维细胞和上皮细胞中以相似的动力学进行复制，但在白细胞嗜性方面存在差异。最后，我们观察到N752突变体对阿非科林（一种靶向病毒聚合酶的药物）的敏感性显著增加（p < 0.001）。我们的结果表明，疱疹病毒酶中的一个单氨基酸变异可影响神经致病潜力，而对受感染动物的病毒排出没有重大影响，这对于病毒在群体中的水平传播很重要。从进化的角度来看，这一观察结果非常有趣，并且与表明N752 DNA pol基因型在EHV-1群体中占主导地位的数据一致，这表明天然宿主中病毒致病性的降低可能不会以个体间传播效率降低为代价。
