Kristensen, C.; Jensen, H. E.; Trebbien, R.; Webby, R. J.; Larsen, L. E.

An outbreak of H5N1 highly pathogenic influenza A virus (HPIAV) has been detected in dairy cows in the United States. Influenza A virus (IAV) is a negative-sense, single-stranded, RNA virus that has not previously been associated with widespread infection in cattle. As such, cattle are an extremely under-studied domestic IAV host species. IAV receptors on host cells are sialic acids (SAs) that are bound to galactose in either an 2,3 or 2,6 linkage. Human IAVs preferentially bind SA-2,6 (human receptor), whereas avian IAVs have a preference for 2,3 (avian receptor). The avian receptor can further be divided into two receptors: IAVs isolated from chickens generally bind more tightly to SA-2,3-Gal-{beta}1,4 (chicken receptor), whereas IAVs isolated from duck to SA-2,3-Gal-{beta}1,3 (duck receptor). We found all receptors were expressed, to a different degree, in the mammary gland, respiratory tract, and cerebrum of beef and/or dairy cattle. The duck and human IAV receptors were widely expressed in the bovine mammary gland, whereas the chicken receptor dominated the respiratory tract. In general, only a low expression of IAV receptors was observed in the neurons of the cerebrum. These results provide a mechanistic rationale for the high levels of H5N1 virus reported in infected bovine milk and show cattle have the potential to act as a mixing vessel for novel IAV generation.