I don't think viruses are the best comparison. Viruses live inside living cells of other organisms and spread. I can't think of an analogy with people. If I take your definition, then I have to disagree there too. It is basically assuming that all humans only have a destructive impact on the earth. There are certainly humans that improve the earth around them. Once I visited a small farm in Brazil. It was run by an older woman from Switzerland. She had take a piece of land in the desert and completely brought it to life. There were so many different plants there. I think this is a good example of a human actually helping rather than bringing down.