Upper respiratory tract infections with Equid Herpesvirus 1 (EHV-1) typically result in a peripheral blood mononuclear cell-associated viremia, which can lead to vasculopathy in the central nervous system. Primary EHV-1 infection also likely establishes latency in trigeminal ganglia (TG) via retrograde axonal transport and in respiratory tract-associated lymphatic tissue. However, latency establishment and reactivation are poorly understood. To characterize the pathogenesis of EHV-1 latency establishment and maintenance, two separate groups of yearling horses were experimentally infected intranasally with EHV-1, strain Ab4, and euthanized 30 days post infection (dpi), (n = 9) and 70 dpi (n = 6). During necropsy, TG, sympathetic trunk (ST), retropharyngeal and mesenteric lymph nodes (RLn, MesLn) and kidney samples were collected. Viral DNA was detected by quantitative PCR (qPCR) in TG, ST, RLn, and MesLn samples in horses 30 and 70 dpi. The number of positive TG, RLn and MesLn samples was reduced when comparing horses 30 and 70 dpi and the viral copy number in TG and RLn significantly declined from 30 to 70 dpi. EHV-1 late gene glycoprotein B reverse transcriptase PCR and IHC results for viral protein were consistently negative, thus lytic replication was excluded in the present study. Mild inflammation could be detected in all neural tissue samples and inflammatory infiltrates mainly consisted of CD3+ T-lymphocytes (T-cells), frequently localized in close proximity to neuronal cell bodies. To identify latently infected cell types, in situ hybridization (ISH, RNAScope®) detecting viral DNA was used on selected qPCR- positive neural tissue sections. In ganglia 30 dpi, EHV-1 ISH signal was located in the neurons of TG and ST, but also in non-neuronal support or interstitial cells surrounding the neuron. In contrast, distinct EHV-1 signal could only be observed in neurons of TG 70 dpi. Overall, detection of latent EHV-1 in abdominal tissue samples and non-neuronal cell localization suggests, that EHV-1 uses T-cells during viremia as alternative route toward latency locations in addition to retrograde neuronal transport. We therefore hypothesize that EHV-1 follows the same latency pathways as its close relative human pathogen Varicella Zoster Virus.

Equid疱疹病毒1（EHV-1）的上呼吸道感染通常会导致外周血单核细胞相关病毒血症，从而导致中枢神经系统血管病变。原发性EHV-1感染还可能通过逆行轴突运输和呼吸道相关淋巴组织在三叉神经节（TG）中建立潜伏期。但是，对延迟建立和重新激活的了解很少。为了表征EHV-1潜伏期建立和维持的发病机理，分别对两组独立的一岁马进行了鼻内EHV-1，Ab4毒株的实验性感染，并在感染后30天（dpi）安乐死（ñ = 9）和70 dpi（ñ= 6）。尸检期间，收集TG，交感神经干（ST），咽后和肠系膜淋巴结（RLn，MesLn）和肾脏样本。通过定量PCR（qPCR）在30 dpi和70 dpi的马中的TG，ST，RLn和MesLn样品中检测病毒DNA。比较马匹30和70 dpi时，阳性TG，RLn和MesLn样品的数量减少，TG和RLn中的病毒拷贝数从30 dpi显着降低到70 dpi。EHV-1晚期基因糖蛋白B逆转录酶PCR和IHC检测病毒蛋白的结果始终为阴性，因此本研究不包括裂解复制。在所有神经组织样本中均可检测到轻度炎症，炎症浸润主要由CD3 + T淋巴细胞（T细胞）组成，通常位于神经元细胞体附近。为了识别潜伏感染的细胞类型，原位在选定的qPCR阳性神经组织切片上使用检测病毒DNA的杂交（ISH，RNAScope®）。在神经节30 dpi中，EHV-1 ISH信号位于TG和ST的神经元中，但也位于神经元周围的非神经支持或间质细胞中。相反，只有在TG 70 dpi的神经元中才能观察到独特的EHV-1信号。总体而言，检测腹部组织样品中潜在的EHV-1和非神经元细胞定位表明，EHV-1在病毒血症期间除了逆行神经元转运外，还使用T细胞作为潜伏位置的替代途径。因此，我们假设EHV-1与其近亲人类病原体水痘带状疱疹病毒遵循相同的潜伏期路径。