Mode of Parainfluenza Virus Transmission Determines the Dynamics of Primary Infection and Protection from Reinfection

Abstract

Little is known about how the mode of respiratory virus transmission determines the dynamics of primary infection and protection from reinfection. Using non-invasive imaging of murine parainfluenza virus 1 (Sendai virus) in living mice, we determined the frequency, timing, dynamics, and virulence of primary infection after contact and airborne transmission, as well as the tropism and magnitude of reinfection after subsequent challenge. Contact transmission of Sendai virus was 100% efficient, phenotypically uniform, initiated and grew to robust levels in the upper respiratory tract (URT), later spread to the lungs, grew to a lower level in the lungs than the URT, and protected from reinfection completely in the URT yet only partially in the lungs. Airborne transmission through 7.6-cm and 15.2-cm separations between donor and recipient mice was 86%–100% efficient. The dynamics of primary infection after airborne transmission varied between individual mice and included the following categories: (a) non-productive transmission, (b) tracheal dominant, (c) tracheal initiated yet respiratory disseminated, and (d) nasopharyngeal initiated yet respiratory disseminated. Any previous exposure to Sendai virus infection protected from mortality and severe morbidity after lethal challenge. Furthermore, a higher level of primary infection in a given respiratory tissue (nasopharynx, trachea, or lungs) was inversely correlated with the level of reinfection in that same tissue. Overall, the mode of transmission determined the dynamics and tropism of primary infection, which in turn governed the level of seroconversion and protection from reinfection. These data are the first description of the dynamics of respiratory virus infection and protection from reinfection throughout the respiratory tracts of living animals after airborne transmission. This work provides a basis for understanding parainfluenza virus transmission and protective immunity and for developing novel vaccines and non-pharmaceutical interventions. Parainfluenza viruses are highly contagious, a leading cause of acute respiratory infection (ARI) in children, often reoccurring, and currently controlled by non-pharmaceutical interventions. We tracked infection and reinfection of a prototypic murine parainfluenza virus after contact or airborne transmission. Our studies reveal that the mode of transmission determines the dynamics of primary infection. Additionally, higher levels of protection from reinfection are induced in individual respiratory tissues by higher levels of primary infection in those same tissues. Natural infection after either contact or airborne transmission tends to initiate in the URT, but not the lungs. Complete protection from infection in the URT was afforded by URT-biased, non-pathogenic infection after low-dose intranasal vaccination. Overall, the data suggest that parainfluenza virus transmission may be effectively controlled by handwashing, disinfection of surfaces, and environmental control of short-range transmission, in addition to the development of live attenuated vaccines that target the URT.