Evidence that spontaneous reactivation of herpes virus does not occur in mice

Some species, including humans and rabbits, exhibit periodic viral reactivation and shed infectious virus at the infected end organ. Mice may be an exception, because spontaneous shedding of infectious virus rarely, if ever, occurs. However, spontaneous molecular reactivation, i.e., the expression of a few viral genes and the synthesis of the viral glycoproteins coded for by these genes, has been reported. This finding has prompted the assumption that molecular reactivation is an indicator of reactivation and the production of infectious virus. The goal of this study was to differentiate between viral gene expression during latency and the episodic production of infectious virus in mice. Viral reactivation and infection were not seen in herpes simplex virus type 1 (HSV-1) latent ganglion graft recipient BALB/c scid or immunocompetent BALB/c mice, which survived the 65-day observation period with no evidence of viral infection although the immunocompetent mice developed cellular and humoral immunity to HSV-1. In contrast, BALB/c scid recipients of ganglia containing reactivating virus invariably developed a local and, subsequently, systemic viral infection and died within 14 days. Immunocompetent BALB/c mice that received ganglion grafts containing reactivating virus survived the infection and became immune to the virus. Trigeminal ganglia removed from scid and immunocompetent recipient graft sites 5, 14, and 28 days after transplantation contained latent virus and viable neurons. The results suggest that, within the limits of detection of the experiments, spontaneous episodic production of immunogenic viral antigens but not of infectious virus occurs in mouse neural ganglia during latency.