An in vitro model to evaluate virus aerosol characteristics using a GFP-expressing adenovirus

Assessment of virus aerosol characteristics is important in designing methods for controlling infectious virus aerosols. The factors relevant to aerosol characteristics include aerosol particle size, concentration, infectivity and virulence. To investigate these characteristics and their changes in different environmental conditions, a laboratory model is required. In this study, replication-deficient recombinant adenovirus (RDRADS) encoding green fluorescent protein (GFP) was used as a model virus. Model virus aerosols were generated using a TK-3 aerosol generator attached to a chamber which could simulate different environmental conditions. Virus aerosol specimens were collected with an FA-1 six-stage impact sampler. The relative genome copy number of viruses in the aerosol was determined by real-time fluorescence quantitative PCR. The number of virus-infected PK15 (pig kidney) cells was determined by counting cells with green fluorescence under a fluorescence microscope at 48 h post-inoculation. Fifteen experiments in different conditions were performed. We found that the viral DNA was present in stages 4-6 of the sampler, with the peak value at stage 5, corresponding to aerosols with a particle size of 0.65-3.3 mum. PK15 cells with green fluorescence showed the same size distribution range at temperatures >29 degrees C and above, where no green fluorescent cells were found, while the genome copy number assayed by real-time PCR remained unchanged. In the presence of high concentrations of particulate matter created by burning biomass, the peak value of virus genome copy number and green fluorescent cell counts shifted to stage 4 of the sampler, corresponding to aerosols with a particle size of 2.1-3.3 mum. The results provide evidence that viruses are present in the atmosphere as aerosols, which are much larger than their own particle size, and that the viruses in the aerosols are affected by atmospheric conditions. Our laboratory model was shown to be feasible for investigating the relationship between the characteristics of viruses and atmospheric conditions.