Viruses are not alive, at least in the classical sense. While they’re made of proteins and genes like living things, they need to interact with living host cells to reproduce. These agents of cellular mayhem have been the cause of history-altering outbreaks and pandemics, from smallpox and polio to HIV and Ebola, but were only discovered at the turn of the 20th century. Since then, we’ve found them in nearly every ecosystem worldwide. Viruses are, and always will be, the world’s experts at going viral.
(Credit: graphicsrf/Shutterstock)
graphicsrf/Shutterstock
Viruses are ultra-tiny packages of genetic material. A single particle, or virion, of influenza is up to 100 times smaller than common bacteria; you could fit some 15,000 end-to-end across the head of a pin. The outer layer is a protective shell called a capsid; some viruses also have a viral envelope, a second layer that helps virions attach to host cells. ...
