**2. RSV virion**

RSV is an enveloped and cytoplasmic virus with non-segmented, negative-sense, single-stranded RNA genome [6]. RSV virions are known to bud out on the infected cell surface. The filamentous virion is up to 12 μm in length and 60 to 200 nm in diameter (**Figure 1**) [7–9]. RSV virions can be irregular-shaped spherical particles with a diameter ranging from 100 to 350 nm. Both filamentous and spherical virus particles mostly remain cell-associated [9].

**Figure 1.** *RSV virion. A photomicrograph of an RSV filamentous virion. The image was taken under electron microscope.*
