fortunately, there is a scientific explanation for everything mate. there is no real proof for "something out there" but rather faith that determines that. the fact that the universe is vast doesn't guarantee that there is something out there either. scientists have looked for planets that have hospitable conditions for life and so far there are only a handful of them in existence within the observable universe. those said planets, however, have lifeforms composed of only bacteria and other relatively simple specimen. in other words, no "alien" can actually travel thousands of light years at a time to make contact with humans, much less leave their own said planets. plagues are instead a matter of disease spread from animal fluids/feces or other contaminants found in certain animal populations. for example, most flues can trace back to a certain animal (aka swine flue, avian flue, etc.).