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, 9 (11), e1003786

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

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

Crystal W Burke et al. PLoS Pathog.

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.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Schematic of experimental and transmission cage design.
(A) Timeline of experiment. For airborne transmission experiments, mice were placed in cages 5 days prior to start of experiment for acclimation. Bioluminescence and weight loss were monitored daily after direct inoculation of donor mice during primary infection and rSeV-luc(M-F*) challenge on day 70 of the experiment. (B) Dimensions and number of mice per cage for contact transmission experiments. (C) Dimensions and number of mice per cage for airborne transmission experiments. In initial experiments, the separation between donor and recipient mice was 7.6 cm. For the longer-range airborne experiments, the left middle divider was moved an additional 7.6 cm to the left for a total separation of 15.2 cm. Solid lines denote solid surfaces that do not permit air flow, and dashed lines indicate stainless steel mesh barriers that permit air flow. D = donor animal, R = recipient animal, and AF = air flow.
Figure 2
Figure 2. Bioluminescence and weight loss in directly inoculated mice.
129X1 mice were inoculated intranasally with 70- (A) or 7,000- (B) PFU of rSeV-luc(M-F*), or PBS (C) and bioluminescence in the nasopharynx (red triangles), trachea (orange circles), and lungs (blue squares) was measured for 14 days. Seventy days after the initial inoculation, the same mice were challenge with a lethal dose of 3×106-PFU of rSeV-luc(M-F*) and bioluminescence was again measured daily. (D) Weight loss was used as a measure of morbidity and was monitored throughout the course of experiment. All numbers are reported as the means ± the standard deviation (70-PFU n = 22 and 7,000-PFU n = 48). The bottom of the y-axis is 5.5×105 photons/s, the limit of detection of bioluminescence.
Figure 3
Figure 3. Dynamics of infection after contact transmission and subsequent challenge.
One 129X1 mouse inoculated intranasally with 70-PFU of rSeV-luc(M-F*) was placed in a cage with 3 naïve mice 24 hours later. Bioluminescence in the (A) nasopharynx, (B) trachea, and (C) lungs was measured daily in the contact mice until infection was cleared (on average 14 days). Seventy days after inoculation of donor mice, the recipients were challenged with 3×106 PFU of rSeV-luc(M-F*) so that reinfection could be monitored by bioluminescence. Each individual mouse is color-coded (n = 6). The bottom of the y-axis is 5.5×105 photons/s, the limit of detection of bioluminescence.
Figure 4
Figure 4. Timing of contact and airborne transmission.
(A) Transmission time based on the mode of transmission and virus inoculum in donor mice. The day of transmission was recorded based on the day of experiment. Day 0 is the day donor mice were directly inoculated intranasally with either 70- or 7,000-PFU of rSeV-luc(M-F*). For contact transmission, naïve recipient mice were caged with donor mice 1 day after direct inoculation. For airborne transmission, naïve recipient mice were caged with infected donor mice directly after inoculation. Reported is the first day when bioluminescence signal exceeded the limit of detection (5.5 log10 photons/sec) in any respiratory tissue. (B) Time of airborne transmission based on whether the dynamics of primary infection were tracheal dominant or respiratory tract disseminated. Significance was determined by Student's t-test: *** p = 0.0003 and ** p = 0.001. n.t. on the y-axis of panel A = no transmission.
Figure 5
Figure 5. Dynamics of Sendai virus infection for representative, individual mice.
Every 24: directly inoculated intranasally with 70-PFU rSeV-luc(M-F*), a contact mouse exposed to a 70-PFU directly inoculated mouse, an airborne-exposed mouse initially infected in the nasopharynx, an airborne-exposed mouse initially infected in the trachea, and an airborne-exposed mouse predominantly infected in the trachea. The data are displayed as radiance (bioluminescence intensity) on a rainbow log scale with a range of 1×106 (blue) to 1×108 (red) photons/s/cm2/steradian (inset).
Figure 6
Figure 6. Primary infection and secondary reinfection in individual mice after airborne transmission across a 7.6-cm separation.
In vivo bioluminescence was measured in individual animals after airborne exposure to donor mice that had been directly inoculated with 70 or 7,000 PFU of rSeV-luc(M-F*). All mice were challenged on day 70 of the experiment with a lethal 3×106-PFU dose of rSeV-luc(M-F*). Mice involved in the airborne transmission experiments were categorized based on the dynamics of the resultant infection: (A) no transmission (1–3), (B) non-productive infection (4), (C) tracheal dominant (5–12), (D) respiratory disseminated with nasopharyngeal first (13–16), and (E) respiratory disseminated with tracheal first (17–21). (F) Bioluminescence curves for two representative mice infected by contact transmission are also included. The bottom of the y-axis is 5.5×105 photons/s, the limit of detection of bioluminescence.
Figure 7
Figure 7. Mean percent weight change during the airborne transmission experiment with a 7.6-cm separation.
For airborne transmission experiments mice were categorized based on the dynamics of infection after transmission. Duplicate contact and triplicate airborne experiments were performed.
Figure 8
Figure 8. Tissue-specific magnitude of Sendai virus infection in the respiratory tracts of living mice after direct inoculation and transmission.
(A–C) Overall magnitude of infection of primary and challenge infections as determined by integration of daily measurements of total flux with respect to time. The areas under the curve (AUC) of bioluminescence are expressed as the total amount of photons on a log10 scale. The association between the magnitude of primary and challenge infection (AUC) in the nasopharynx (D), trachea (E), and lungs (F) was determined using linear regression analysis (r2) with GraphPad Prism software. Data for airborne transmission corresponds to experiments that had a 7.6-cm separation between donor and recipient mice. No trans. = no transmission, trach. dom. = tracheal dominant infection, rep. diss. = respiratory tract disseminated infection.
Figure 9
Figure 9. Sendai virus-specific binding antibody titers. Sera were collected on day 30 of the experiment.
Titers were measured by reciprocal endpoint dilutions in ELISA assays and the fold change in titers over mock inoculated mouse levels was calculated. Data for airborne transmission corresponds to experiments that had a 7.6-cm separation between donor and recipient mice. Significance was determined using the Student's t-test: * p≤0.03 and ** p = 0.004. No trans. = no transmission, trach. dom. = tracheal dominant infection, rep. diss. = respiratory tract disseminated infection.
Figure 10
Figure 10. Primary infection in individual mice after airborne transmission across a 15.2-cm separation.
In vivo bioluminescence was measured in individual animals after airborne exposure to donor mice that had been directly inoculated with 7,000 PFU of rSeV-luc(M-F*). Mice involved in the airborne transmission experiments were categorized based on the dynamics of the resultant infection: (A) tracheal dominant, (B) non-productive infection, (C) respiratory disseminated with nasopharyngeal first, and (D) respiratory disseminated with tracheal first. The bottom of the y-axis is 5.5×105 photons/s, the limit of detection of bioluminescence.

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