Viruses do not evolve with the purpose of being more or less infectious or dangerous: it is just natural selection at work. New random variants occur continuously and most of them are neutral or make the virus less infectious.

If aliens were to examine a human, they would think we were just slavish organisms designed to feed microbes and carry them around. Our bodies contain ten times more bacteria than cells , and there are an estimated 3.

If you can't kill them, trap them. Such is the fate that scientists are reserving to pathogenic bacteria, such as the infamous E. coli .