Influenza is one of the most contagious and rapidly spreading infectious diseases and an important global cause of hospital admissions and mortality. There are some amounts of the virus in the air constantly. These amounts is generally not enough to cause disease in people, due to infection prevention by healthy immune systems. However, at a higher concentration of the airborne virus, the risk of human infection increases dramatically. Early detection of the threshold virus concentration is essential for prevention of the spread of influenza infection. This review discusses different approaches for measuring the amount of influenza A virus particles in the air and assessing their infectiousness. Here we also discuss the data describing the relationship between the influenza virus subtypes and virus air transmission, and distribution of viral particles in aerosol drops of different sizes.

Spherical nanoparticles (SNPs) were generated by two-step thermal remodelling of native tobacco mosaic virus (TMV) at 94 °C. Particles of irregular shape and varying size were generated by TMV at 90 °C. They could be converted into SNPs by heating at 94 °C and were considered to be intermediate precursors of SNPs. In addition to SNP monomers (53 nm diameter), generated by individual TMV virions, large SNPs (100–800 nm diameter) were assembled. The size of the SNPs depended on the TMV concentration. The SNPs could be generated by distinct forms of RNA-free TMV coat protein (CP) aggregates and individual CP subunits. A one-step SNP assembly appeared to occur in these cases. These results show that SNPs represent a new type of particle nanoplatform for producing compositions of SNPs with foreign protein molecules bound to their surface.

Different models have been proposed for the nature of the potexvirus transport form that moves from cell to cell over the infected plant: (i) genomic RNA moves as native virions; or (ii) in vitro-assembled non-virion ribonucleoprotein (RNP) complexes consisting of viral RNA, coat protein (CP) and movement protein (MP), termed TGBp1, serve as the transport form in vivo. As the structure of these RNPs has not been elucidated, the products assembled in vitro from potato virus X (PVX) RNA, CP and TGBp1 were characterized. The complexes appeared as single-tailed particles (STPs) with a helical, head-like structure composed of CP subunits located at the 5′-proximal region of PVX RNA; the TGBp1 was bound to the terminal CP molecules of the head. Remarkably, no particular non-virion RNP complexes were observed. These data suggest that the CP–RNA interactions resulting in head formation prevailed over TGBp1–RNA binding upon STP assembly from RNA, CP and TGBp1. STPs could be assembled from the 5′ end of PVX RNA and CP in the absence of TGBp1. The translational ability of STPs was characterized in a cell-free translation system. STPs lacking TGBp1 were entirely non-translatable; however, they were rendered translatable by binding of TGBp1 to the end of the head. It is suggested that the RNA-mediated assembly of STPs proceeds via two steps. Firstly, non-translatable CP–RNA STPs are produced, due to encapsidation of the 5′-terminal region. Secondly, the TGBp1 molecules bind to the end of a polar head, resulting in conversion of the STPs into a translatable form.