Figure 1.
Arrangement of Infected and Exposed Guinea Pigs in Environmental Chamber
In each experiment, eight animals were housed in a Caron 6030 environmental chamber. Each guinea pig was placed in its own cage, and two cages were positioned on each shelf. Naïve animals were placed behind infected animals, such that the direction of airflow was toward the naïve animals. The cages used were open to airflow through the top and one side, both of which were covered by wire mesh. Although infected and exposed guinea pigs were placed in pairs, air flowed freely between shelves, allowing transmission to occur from any infected to any naïve animal.
Figure 2.
Transmission of Influenza Virus from Guinea Pig to Guinea Pig Is Dependent on Relative Humidity
Titers of influenza virus in nasal wash samples are plotted as a function of day p.i. Overall transmission rate and the RH and temperature conditions of each experiment are stated underneath the graph. Titers from intranasally inoculated guinea pigs are represented as dashed lines; titers from exposed guinea pigs are shown with solid lines. Virus titrations were performed by plaque assay on Madin Darby canine kidney cells.
Figure 3.
Transmission of Influenza Virus from Guinea Pig to Guinea Pig Is Highly Efficient at 5 °C and Blocked at 30 °C
Titers of influenza virus in nasal wash samples are plotted as a function of day p.i. Overall transmission rate and the RH and temperature conditions of each experiment are stated underneath the graph. Titers from intranasally inoculated guinea pigs are represented as dashed lines; titers from exposed guinea pigs are shown with solid lines.
Figure 4.
Guinea Pigs Housed at 5 °C Shed Influenza Virus at Higher Titers on Days 4, 6, and 8 p.i. Than Guinea Pigs Housed at 20 °C
Average viral titers in nasal wash samples collected from animals housed at either 5 °C or 20 °C and all RH tested are plotted as function of time post-infection. Error bars indicate standard deviation; * indicates statistically significant difference between titers at 5 °C and 20 °C, with p ≤ 0.005.
Figure 5.
Antiviral and Pro-Inflammatory Responses Are Similar between Guinea Pigs Housed at 5 °C and 20 °C
Levels of the indicated mRNA transcripts present in nasal turbinates of infected guinea pigs housed at 5 °C (black bars) or 20 °C (grey bars) were quantified by real-time PCR of reverse transcribed mRNA. RNA levels were normalized to β-actin and are expressed as fold-induction over mock-infected guinea pig. Error bars represent standard deviation. * indicates a statistically significant (p < 0.05) difference between 5 °C and 20 °C.
Figure 6.
Variation of Transmission Efficiency with Relative Humidity: A Model
At 20 °C (dashed line), transmission efficiency is highest at low RH, when influenza virions in an aerosol are relatively stable, and desiccation of exhaled respiratory droplets produces droplet nuclei. Transmission is diminished at intermediate RH when virus particles are relatively unstable, but improves in parallel with influenza virus stability at higher humidities. At high RH, evaporation from exhaled particles is limited, respiratory droplets settle out of the air, and transmission is blocked. At 5 °C (solid line), transmission is more efficient than at 20 °C, but is reduced to a rate of 50% at higher humidities.