Viruses are minute infectious particles that require a host to survive, be it an animal, plant and bacterium. Viruses have a simple structure consisting of DNA or RNA enveloped within a protein capsule. These pesky pathogens cause a variety of human diseases, including AIDs, meningitis and the flu. There is some controversy as to whether viruses are alive, as they require a living host cell to replicate, and cannot do so on their own.

I Contain Multitudes by Ed Yong

In our final extract from the Wellcome Book Prize 2017 shortlist, Ed Yong explores the microbiota that teem all over and within our bodies, and the incredible ways they affect our lives.

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Do viruses die?

Viruses exist at the boundary of what counts as life, and most scientists now agree they don't make the cut.