i.c. administration of myxoma virus is safe in nude mice. A, nude mice receiving live vMyxgfp (live vMyxgfp, 12 mice) i.c. showed a slight lose in body weight the first week after virus administration although this was not significantly different than dead myxoma virus–treated (4 mice) animals (two-way ANOVA, P = 0.6360). The mice appeared normal throughout the experiment and none died. B, histologic changes in the brain of live vMyxgfp–treated mice showed mild focal inflammation and some minor lymphocytic and microglial infiltration at the site of viral inoculation (right two columns; top, ×25; bottom, ×400) but not in the dead myxoma virus–treated animals (left column; top, ×25; bottom, ×400). There was no diffuse meningoencephalitis, hydrocephalus, or other significant abnormalities. Casing represents regions that are magnified.