Question: How do viruses come?

David Walker-Sünderhauf answered on 1 Mar 2019:

You can catch a virus from someone else who is infected by it, or from the environment. Unlike bacteria that make you ill, which often just sit inside your body, viruses are actually like little parasites that go directly into your cells. They hijack your own cells’ machinery, and make your cells produce more viruses instead of doing what they are meant to. Once it has made enough new viruses, the cell explodes, this releases all the new viruses which can go on to infect other cells in your body, or other people.
There is actually a different type of virus, called bacteriophage, which works in the same way but can only infect bacteria – not humans! Scientists are looking at using bacteriophage to help cure bacterial diseases by killing the bacteria for you, so viruses like this might actually help us, which I find pretty cool 🙂