Susceptibility of bovine respiratory and mammary epithelial cells to avian and mammalian derived clade 2.3.4.4b H5N1 highly pathogenic avian influenza viruses

Zoonotic transmission of avian influenza viruses into mammals is relatively rare due to anatomical differences in the respiratory tract between species. Recently, clade 2.3.4.4b highly pathogenic H5N1 avian influenza viruses were detected circulating in North American cattle. Sporadic transmission between cattle, humans, and other animals proximal to cattle or after consuming products from infected cattle has occurred, but thus far there is no evidence of human-to-human transmission. However, the virus has the potential to adapt to the mammalian respiratory tract with every transmission event that occurs, making it crucial to understand cellular and species tropism of the H5N1 2.3.4.4b viruses. We compared viral kinetics of clade 2.3.4.4b viruses isolated from birds and mammals in respiratory epithelial cells derived from cattle, human, swine, and ferret. We found that avian derived viruses could replicate in swine cells only, yet mammalian derived strains could replicate efficiently in all tracheal and nasal epithelial cells tested. Interestingly, only bovine mammary epithelial cells (MEC) and swine respiratory epithelial cells were permissive to both avian and mammalian derived strains, possibly due to increased sialic acid expression on bovine MEC compared to bovine tracheal epithelial cells (TEC). However, sialic acid expression differed between dairy and beef cows: TEC derived from a dairy cow had increased expression of 2,3 sialic acid receptors compared to TEC from a beef-dairy cow cross. This study highlights the ability of clade 2.3.4.4b H5N1 viruses derived from mammals but not wild birds to infect the respiratory epithelium of other mammalian hosts.