Whole animal imaging allows viral replication and localization to be monitored in intact animals, which provides significant advantages for determining viral and host factors that determine pathogenesis. To investigate effects of
interferons on spatial and temporal progression of
vaccinia infection, we generated recombinant viruses that express
firefly luciferase or a monomeric orange fluorescent
protein. These viruses allow
vaccinia infection to be monitored with bioluminescence or fluorescence imaging, respectively. The recombinant viruses were not attenuated in vitro or in vivo relative to a control WR virus. In cell culture, reporters could be detected readily by 4 h post-
infection, showing that these viruses can be used as early markers of
infection. The magnitude of
firefly luciferase activity measured with bioluminescence imaging in vitro and in vivo correlated directly with increasing titers of vaccinia virus, validating imaging data as a marker of
viral infection. Replication of
vaccinia was significantly greater in mice lacking receptors for
type I interferons (IFN I R-/-) compared with wild-type mice, although both genotypes of mice developed
focal infections in lungs and brain after intranasal inoculation. IFN I R-/- mice had greater dissemination of virus to liver and spleen than wild-type animals even when mortality occurred at the same time point after
infection. Protective effects of
type I interferons were mediated primarily through parenchymal cells rather than hematopoietic cells as analyzed by bone marrow transplant experiments. Collectively, our data define a new function for
type I interferon signaling in systemic dissemination of
vaccinia and validate these reporter viruses for studies of pathogenesis.