https://theconversation.com/how-to-flatten-the-curve-of-coronavirus-a-mathematician-explains-133514

A  virus  is a small parasite that cannot reproduce by itself. Once it infects a susceptible cell, however, a  virus  can direct the cell machinery to produce more viruses. Most viruses have either  RNA  or  DNA  as their genetic material. The  nucleic acid  may be single- or double-stranded. The entire infectious virus particle, called a  virion , consists of the nucleic acid and an outer shell of  protein . The simplest viruses contain only enough RNA or DNA to encode four proteins. The most complex can encode 100 – 200 proteins. https://www.ncbi.nlm.nih.gov/books/NBK21523/figure/A1410/?report=objectonly