Establishment And Identification Of HSV-1 Latency Infection In The Tree Shrew Model

Herpes simplex viruses(HSV) is a most common human pathogen, establish life long infection in more than 80% of the population and their reactivation leads to oral, cornea and genital herpes. Some recover virus may enter the central central ner vous system(CNS) by axon, and is known to be causative of herpes simplex viral encephalitis(HSE), results in inreversible neuronal damage, even death. C urrently rodent models are the preferred models for latency stud ies, however they are distant from primates and may not fully represent human latency. The tree shrew(Tupaia belangeri chinensis) is a small mammal, a prosimian primate, indigenous to southwest Asia. At behavioral, anatomical, genomic and evolutional levels, tree shrews are much closer to primates than rodents. Research finding that tree shrew is susceptive to HSV-1. However, so far there isn’t in-depth study to tree shrew latency infection model. In an attempt to further develop the tree shrew as a useful model to study herpes virus infection, we studied the establishment of latency and reactivation of HSV-1 in tree shrews trige mina l ga nglia(TG), C N S and eye, following ocular inoculation.In the trige minal ganglia(TG) of tree shrew peripheral nervous system, by immunohistoc he mistry(IHC), immuno fluorescent(IF), in sit u hybrid izatio n, PC R and q R T- PC R, we found that HSV-1 indeed establish latency in the sensory neurons of tree shrew TG, and could be stress reactivated to produce infectious virus, following explant co-cultivation and that spo ntaneous reactivation could be detected by cell culture of eye tears. Interestingly, the tree shrew model is quite different from the mouse model of HSV infection, in that the virus exhibited only a mild acute infection following inoculation with no detectable infectious virus from the sensory neurons. O n the contrary, plenty of live virus and HSV-1 protein occurred in the mouse TG. The mild infection may be more similar to human infection in that the sensory neurons continue to function after herpes reactivation and the affected skin tissue does not lose sensation, and also seldom come up HSE.During acute state of the infection, a portion of the severely infected tree shrews exhibit symptoms similar to human HSE, manifested by anorexia, lethargy, ataxia, torticollis and abnormal whirl before perishing during the acute stage. We studied that presence of the virus in the CNS during the entire course of our study and found that the virus enter the CNS one week following eye inoculation, and produced lytic infection in olfactory bulbs and brain stem, two likely port of entry into the CNS, followed by latency. Using a modified explant cocultivation technique, we were able to recover reactivated virus from infected tree shrew brain, suggesting that the HSV-1 virus latently infects the tree shrew CNS, and virus reactivation in situ brain. The results are great significance to study HSE.During the acute stage the infected tree shrew also developed the eye disease similar to the human herpes simplex viral keratitis(HSK). During acute stage, live virus and viral products could be detected in the cornea and the retinal neurons. During latency, live virus could be recovered from supernatant of cornea and optical nerves, suggesting spontaneous reactivation of the virus.Taken together, these analyses strongly suggest that the tree shrew model of HSV-1 infection has several advantages compared to rodent models. Thus, the tree shrew is a viable model to study HSV latency, pathogenesis in the HSE and HSK.