Seasonal influenzaviruses decay more rapidly at intermediate humidity in droplets containing saliva compared to respiratory mucus

Abstract

Expulsions of virus-laden aerosols or droplets from the oral and nasal cavities of an infected host are an important source of onward respiratory virus transmission. However, the presence of infectious influenzavirus in the oral cavity during infection has not been widely considered, and thus, little work has explored the environmental persistence of influenzavirus in oral cavity expulsions. Using the ferret model, we detected infectious virus in the nasal and oral cavities, suggesting that the virus can be expelled into the environment from both anatomical sites. We also assessed the stability of two influenzaA viruses (H1N1 and H3N2) in droplets of human saliva or respiratory mucus over a range of relative humidities. We observed that influenzavirus infectivity decays rapidly in saliva droplets at intermediate relative humidity, while viruses in airway surface liquid droplets retain infectivity. Virus inactivation was not associated with bulk protein content, salt content, or droplet drying time. Instead, we found that saliva droplets exhibited distinct inactivation kinetics during the wet and dry phases at intermediate relative humidity, and droplet residue morphology may lead to the elevated first-orderinactivation rate observed during the dry phase. Additionally, distinct differencesin crystalline structure and nanobead localization were observed between saliva and airway surface liquid droplets. Together, our work demonstrates that differentrespiratory fluidsexhibit unique virus persistence profilesand suggests that influenzaviruses expelled from the oral cavity may contribute to virus transmission in low- and high-humidity environments.