- Why do humans not have to be concerned about the presence of bacteriophages in their food?
- What are three ways that viruses can be transmitted between hosts?
Viral Structures
In general, virions (viral particles) are small and cannot be observed using a regular light microscope. They are much
smaller than prokaryotic and eukaryotic cells; this is an adaptation allowing viruses to infect these larger cells (see
Figure 6.3). The size of a virion can range from 20 nm for small viruses up to 900 nm for typical, large viruses (see
Figure 6.4). Recent discoveries, however, have identified new giant viral species, such asPandoravirus salinusand
Pithovirus sibericum, with sizes approaching that of a bacterial cell.[7]
Figure 6.3 (a) In this transmission electron micrograph, a bacteriophage (a virus that infects bacteria) is dwarfed by
the bacterial cell it infects. (b) An illustration of the bacteriophage in the micrograph. (credit a: modification of work by
J.P. Nataro and S. Sears, Centers for Disease Control and Prevention—scale-bar data from Matt Russell)
- N.Philippe et al. “Pandoraviruses: Amoeba Viruses with Genomes up to 2.5 Mb Reaching that of Parasitic Eukaryotes.” Science 341,
no. 6143 (2013): 281–286.
Chapter 6 | Acellular Pathogens 233