What is a virus?

Viruses are tiny organisms that can infect living hosts, such as humans, animals, or plants. They consist of a small amount of genetic material (either DNA or RNA) encased in a protective shell called a capsid. Unlike other organisms, viruses cannot reproduce on their own and need a host to replicate. Some viruses also have an additional outer layer called an envelope, which can have proteins that help the virus attach to and enter host cells.