Uninfected ferret corneal epithelial sheets were dissociated from excised whole ferret eyes following incubation in tetrasodium EDTA for determination of expression of surface sialoligosaccharides as previously described [20, 58] . To assess virus dissemination, ferrets were inoculated with NL/219-FL virus either i.o. (100 ml) or i.n. (1 ml) as previously described [32] . Fifteen minutes p.i., ferrets were euthanized and respiratory and ocular tissues were excised for ex vivo imaging using a Spectrum in vivo imaging system and Living Image 4.0 Software (Caliper Life Sciences). All ex vivo imaging was performed in triplicate. To quantify the presence of NL/219-FL virus in excised tissues, regions of interest were drawn around each tissue using Living Image 4.0 Software to obtain maximum relative efficiency values for each tissue, expressed as photons/second/cm 2 /steradian, the mean of which was generated from three ferrets per tissue as expressed in Figure 3 .