ABSTRACT The ongoing transmission of influenza A viruses (IAV) for the past century continues to be a burden to humans. IAV binds terminal sialic acids (SA) of sugar molecules present within the upper respiratory tract (URT) in order to successfully infect hosts. The two most common SA structures that are important for IAV infection are those with α2,3- and α2,6-linkages. While mice were once considered to be an unsuitable system for studying IAV transmission due to their lack of α2,6-SA in the trachea, we have successfully demonstrated that IAV transmission in infant mice is remarkably efficient. This finding led us to reevaluate the SA composition of the URT of mice using in situ immunofluorescence and examine its in vivo contribution to transmission for the first time. We demonstrate that mice express both α2,3- and α2,6-SA in the URT and that the difference in expression between infants and adults contribute to the variable transmission efficiencies observed. Furthermore, selectively blocking α2,3-SA or α2,6-SA within the URT of infant mice using lectins was necessary but insufficient at inhibiting transmission, and simultaneous blockade of both receptors was crucial in achieving the desired inhibitory effect. By employing a broadly-acting neuraminidase (ba-NA) to indiscriminately remove both SA moieties in vivo , we effectively suppressed viral shedding and halted the transmission of different strains of influenza viruses. These results emphasize the utility of the infant mouse model for studying IAV transmission, and strongly indicate that broadly targeting host SA is an effective approach that inhibits IAV contagion. IMPORTANCE Influenza virus transmission studies have historically focused on viral mutations that alter hemagglutinin binding to sialic acid (SA) receptors in vitro . However, SA binding preference doesn’t fully account for the complexities of IAV transmission in humans. Our previous findings reveal that viruses that are known to bind α2,6-SA in vitro have different transmission kinetics in vivo , suggesting that diverse SA interactions may occur during their life-cycle. In this study, we examine the role of host SA on viral replication, shedding, and transmission in vivo . We highlight the critical role of SA presence during virus shedding, such that attachment to SA during virion egress is equally important as detachment from SA during virion release. These insights support the potential of broadly-acting neuraminidases as therapeutic agents capable of restraining viral transmission in vivo . Our study unveils intricate virus-host interactions during shedding, highlighting the necessity to develop innovative strategies to effectively target transmission.

Targeting host sialic acids in the upper respiratory tract with a broadly-acting neuraminidase to inhibit influenza virus transmission