Quite a large number of the natural viruses our there aren't even all that harmful to us. The most deadly ones were created by us indirectly through the indiscriminate use of anti-biotics. Other were transferred to us because we were doing things that were harmful to ourselves and our world to begin with, such as the spread of HIV from monkey's to humans. -As a retired physician I can't let this slip by. Viruses are NOT affected by antibiotics. Antibiotics treat bacteria. Anti-virals treat viruses. The most deadly viruses figured it out to be nasty all by themselves.