Illumination of Parainfluenza Virus Infection and Transmission in Living Animals Reveals a Tissue-Specific Dichotomy

Abstract

The parainfluenza viruses (PIVs) are highly contagious respiratory paramyxoviruses and a leading cause of lower respiratory tract (LRT) disease. Since no vaccines or antivirals exist, non-pharmaceutical interventions are the only means of control for these pathogens. Here we used bioluminescence imaging to visualize the spatial and temporal progression of murine PIV1 (Sendai virus) infection in living mice after intranasal inoculation or exposure by contact. A non-attenuated luciferase reporter virus (rSeV-luc(M-F*)) that expressed high levels of luciferase yet was phenotypically similar to wild-type Sendai virus in vitro and in vivo was generated to allow visualization. After direct intranasal inoculation, we unexpectedly observed that the upper respiratory tract (URT) and trachea supported robust infection under conditions that result in little infection or pathology in the lungs including a low inoculum of virus, an attenuated virus, and strains of mice genetically resistant to lung infection. The high permissivity of the URT and trachea to infection resulted in 100% transmission to naïve contact recipients, even after low-dose (70 PFU) inoculation of genetically resistant BALB/c donor mice. The timing of transmission was consistent with the timing of high viral titers in the URT and trachea of donor animals but was independent of the levels of infection in the lungs of donors. The data therefore reveals a disconnect between transmissibility, which is associated with infection in the URT, and pathogenesis, which arises from infection in the lungs and the immune response. Natural infection after transmission was universally robust in the URT and trachea yet limited in the lungs, inducing protective immunity without weight loss even in genetically susceptible 129/SvJ mice. Overall, these results reveal a dichotomy between PIV infection in the URT and trachea versus the lungs and define a new model for studies of pathogenesis, development of live virus vaccines, and testing of antiviral therapies.

Relationships among Dissemination of Primary Parainfluenza Virus Infection in the Respiratory Tract, Mucosal and Peripheral Immune Responses, and Protection from Reinfection: a Noninvasive Bioluminescence-Imaging Study

“…Working stocks of recombinant Enders strain Sendai viruses rSeV-luc(M-F*) and rSeV-luc(P-M) were generated and characterized in vitro and in vivo previously (16,24). In brief, the viruses were rescued by reverse genetics in LLC-MK2 cells, propagated twice in the allantoic cavities of 10-day-old embryonated eggs, plaque purified by LLC-MK2 cells, and confirmed to contain no mutations by reverse transcription-PCR (RT-PCR) and sequencing.…”

“…To enable the visualization of Sendai virus infection and reinfection noninvasively in living mice, we previously developed both nonattenuated and attenuated luciferase-expressing reporter viruses (24). Similar bioluminescence-imaging systems have also been developed for vaccinia virus (25), herpes simplex virus 1 (HSV-1) (26), Sindbis virus (27), dengue virus (28), and influenza virus (29,30).…”

“…Similar bioluminescence-imaging systems have also been developed for vaccinia virus (25), herpes simplex virus 1 (HSV-1) (26), Sindbis virus (27), dengue virus (28), and influenza virus (29,30). Wild-type Sendai virus and the nonattenuated reporter virus rSeV-luc(M-F*) have similar growth rates in cell culture and in the respiratory tracts of mice; moreover, both viruses induce similar levels of morbidity and mortality, T-cell infiltration into bronchoalveolar lavage fluid (BALF), cytokine profiles, and Sendai virus-specific antibody responses (24). Similar to HPIVs and wild-type Sendai virus (31)(32)(33), rSeV-luc(M-F*) is transmitted most efficiently by contact transmission but also by the shortrange airborne route (16).…”

“…Noninvasive bioluminescence imaging of Sendai virus infection revealed a dichotomy in the respiratory tract (24). The upper respiratory tract (URT) was found to support high levels of infection (even under conditions of a low-dose inoculation, virus attenuation, or a low level of host susceptibility to pulmonary infection) and efficiently promote contact transmission even in the absence of substantial infection in the lungs.…”

“…In contrast, high levels of infection in the lungs and the concomitant host response were responsible for disease severity. Thus, there appears to be a separation of transmissibility and pathogenicity for Sendai virus in mice (24). Further use of the imaging system revealed that natural infections after short-range airborne transmission are anisotropic, initiating in either the nasopharynx or trachea before either remaining localized or disseminating throughout the respiratory tract (16).…”