1/8 I realize from reading many posts that there is a lot of misunderstanding about viruses. So let me write a bit about viruses, my favorite subject for nearly 50 years. I’m writing for non-virologists so I’ll try to keep this understandable. I’m going to cover just a few basic topics; I can do more in the future if it’s wanted. First, it’s important to understand how tiny viruses are. The known viruses that infect humans range in size from 25 to 300 nanometers (nm).