Genital re-excretion of Murid gammaherpesvirus 4 following intranasal infection

Gammaherpesviruses are the archetypes of persistent viruses that have been identified in a range of animals from mice to man. They are host-range specific and establish persistent, productive infections of immunocompetent hosts. Thus, infected individuals simultaneously both elicit antiviral protective immune response and secrete infectious virions. The best studied gammaherpesviruses are Human herpesvirus 4 and Human herpesvirus 8. As these viruses have no well-established in vivo infection model, related animal gammaherpesviruses are an important source of information. We are studying Murid herpesvirus 4 (MuHV-4), a virus that has originally been isolated from bank voles (Myodes glareolus). Although MuHV-4 has not been isolated from house mice (Mus musculus), infection of inbred laboratory mouse strains is commonly accepted as a good model for studying gammaherpesviruses in vivo. To date, it has however never been possible to monitor viral reexcretion and virus transmission in this species suggesting that this model could be imperfect. In order to identify potential re-excretion sites, intranasally infected mice were followed through global luciferase imaging for up to six months after infection. By this technique, we were able to detect appearance of viral replication in mice genital tract at various times post-infection. Typically, it firstly occurred between days 20 to 30 after infection, a period at which it is admitted that latency is established. Ex vivo imaging, quantitative PCR and immunohistochemistry helped us to determine that virus genomes were present in high quantity in the vaginal tissue and that viral replication occurred mainly at the vaginal external border. Finally, we highlighted the presence of free infectious viruses in the vaginal cavity at the moment of the observation of viral replication. In conclusion, we experimentally indentified for the first time a reexcretion site for MuHV-4 in mice that had been intranasaly infected. It therefore suggests potential genital transmission, either horizontal or vertical, of this virus in mice populations. In the future, these results could help us to better understand the biology of gammaherpesviruses but should also allow us to develop vaccinal strategies that could prevent the spread of these viruses in natural populations.