The high similarity of respiratory tract tissue between humans and ferrets makes the ferret model an attractive one for modeling human respiratory disease and investigating the role of receptor specificity in influenza virus pathogenesis, providing an advantage over murine models [25] . We found that the sialic acid composition of ferret corneal epithelial sheets more closely mimics that of humans compared with a mouse model, demonstrating another physiological parallel between ferrets and humans [20] . Bridging the a2-3 rich corneal and conjunctival epithelial surfaces with a2-6 rich upper respiratory tract tissue is the lacrimal duct, which expresses both a2-3 and a2-6 linked sialic acids [14, 34] . Characterization of the distribution of sialic acids in the ferret conjunctiva and lacrimal duct, in addition to the composition of ferret ocular mucins, will allow for a better understanding of virus attachment and replication in these locations. However, in a previous study, we demonstrated that the ability of influenza viruses to bind to or replicate in ocular tissue cannot be explained by sialic acid binding specificity alone [20] . Our detection in ferret ocular tissue of both human and avian influenza viruses with distinct binding specificities further underscores this point (Table 4 , Figure 3 ).