Herpes Simplex Virus 1 Infection of Tree Shrews Differs from That of Mice in the Severity of Acute Infection and Viral Transcription in the Peripheral Nervous System

Abstract

Studies of herpes simplex virus (HSV) infections of humans are limited by the use of rodent models such as mice, rabbits, and guinea pigs. Tree shrews (Tupaia belangeri chinensis) are small mammals indigenous to southwest Asia. At behavioral, anatomical, genomic, and evolutionary levels, tree shrews are much closer to primates than rodents are, and tree shrews are susceptible to HSV infection. Thus, we have studied herpes simplex virus 1 (HSV-1) infection in the tree shrew trigeminal ganglion (TG) following ocular inoculation. In situ hybridization, PCR, and quantitative reverse transcription-PCR (qRT-PCR) analyses confirm that HSV-1 latently infects neurons of the TG. When explant cocultivation of trigeminal ganglia was performed, the virus was recovered after 5 days of cocultivation with high efficiency. Swabbing the corneas of latently infected tree shrews revealed that tree shrews shed virus spontaneously at low frequencies. However, tree shrews differ significantly from mice in the expression of key HSV-1 genes, including ICP0, ICP4, and latency-associated transcript (LAT). In acutely infected tree shrew TGs, no level of ICP4 was observed, suggesting the absence of infection or a very weak, acute infection compared to that of the mouse. Immunofluorescence staining with ICP4 monoclonal antibody, and immunohistochemistry detection by HSV-1 polyclonal antibodies, showed a lack of viral proteins in tree shrew TGs during both acute and latent phases of infection. Cultivation of supernatant from homogenized, acutely infected TGs with RS1 cells also exhibited an absence of infectious HSV-1 from tree shrew TGs. We conclude that the tree shrew has an undetectable, or a much weaker, acute infection in the TGs. Interestingly, compared to mice, tree shrew TGs express high levels of ICP0 transcript in addition to LAT during latency. However, the ICP0 transcript remained nuclear, and no ICP0 protein could be seen during the course of mouse and tree shrew TG infections. Taken together, these observations suggest that the tree shrew TG infection differs significantly from the existing rodent models. IMPORTANCEHerpes simplex viruses (HSVs) establish lifelong infection in more than 80% of the human population, and their reactivation leads to oral and genital herpes. Currently, rodent models are the preferred models for latency studies. Rodents are distant from primates and may not fully represent human latency. The tree shrew is a small mammal, a prosimian primate, indigenous to southwest Asia. In an attempt to further develop the tree shrew as a useful model to study herpesvirus infection, we studied the establishment of latency and reactivation of HSV-1 in tree shrews following ocular inoculation. We found that the latent virus, which resides in the sensory neurons of the trigeminal ganglion, could be stress reactivated to produce infectious virus, following explant cocultivation and that spontaneous reactivation could be detected by cell culture of tears. Interestingly, the tree shrew model is quite different from...

Experimental Oral Herpes Simplex Virus-1 (HSV-1) Co-infection in Simian Immunodeficiency Virus (SIV)-Infected Rhesus Macaques

“…Prior comparisons of HSV-1 F and HSV-1 McKrae in mouse models have demonstrated that McKrae is more pathogenic and requires a lower dose to induce morbidity and mortality in mice than HSV-1 F (Dix et al, 1983 ; Wang et al, 2013 ). McKrae also does not require scarification for ocular infection in tree shews (Li et al, 2016 ). Due to the limitations of this pilot experiment, we were unable to test oral inoculation of macaques with McKrae in absence of abrasion to determine whether it would be possible.…”

“…NHP models of HSV-1 infection are largely in new world species: squirrel monkeys (by corneal scarification and infection with strains McKrae or Rodanus) (Kaufman, 1963 ; Varnell et al, 1987 , 1995 ; Rootman et al, 1990 ); and owl monkeys and marmosets (by intracerebral injection with strain F) (Katzin et al, 1967 ; Hunter et al, 1999 ; Deisboeck et al, 2003 ). Tree shrews, which are prosimians, are susceptible ocularly to HSV-1 17+ after scarification and atraumatically with McKrae (Li et al, 2016 ). However, these models result in acute dendritic keratitis or encephalitis following HSV-1 infection, and new world NHPs are not susceptible to SIV.…”

Comparative Pathogenicity and Transmissibility of Pandemic H1N1, Avian H5N1, and Human H7N9 Influenza Viruses in Tree Shrews

“…Since 1970s, tree shrews have been used as animal models for various viruses. Herpes simplex virus (HSV) was the first virus known to infect tree shrews, and tree shrews proved to be a viable model to study HSV latency (Darai et al, 1978;Li et al, 2015Li et al, , 2016. Moreover, the tree shrew was the only non-primate animal found to be susceptible to hepatitis B virus (HBV) infection, and therefore was used to study HBV infection for many years (Guo et al, 2018).…”

Primary Tree Shrew Dermis Fibroblasts Support Lytic Replication of Human Cytomegalovirus

“…Meanwhile, it has economical maintenance costs and a small body size. These advantages enable its application in pathological research of many human viruses including Herpes simplex virus type 1 [12,13]. For HCMV, these advantages suggest a potential susceptibility of the Chinese tree shrew to this viral infection.…”