In an attempt to specifically address the role of monocyte/macrophages in control of virus replication at the site of infection and the spread of VACV systemically, we utilized Macrophage Fas-Induced Apoptosis (MAFIA) mice which encode both a suicide gene and Green Fluorescent Protein (GFP) driven by the c-fms (CD115/MCSF receptor) promoter [21]. The gene discussed is CSF1R; the disease is infection.