To expound on this point, to a virus or bacteria, a human is just as good as a monkey or dog or jellyfish. It's a place to replicate and live. Similar with viruses as technically they are not alive. All these Dr. Doom kinda things have to compete with the common cold, the e. coli, and all the other things that live on the earth and in your guts. That is not an easy environment to survive in.