It seems like a new virus that’s trying to kill us pops up somewhere in the world every other day. The World Health Organization recently announced that it is monitoring a new contagious, respiratory-infection-inducing coronavirus (suggested codename: Middle East respiratory syndrome coronavirus or MERS-Cov) that is responsible for dozens of illnesses and several deaths in the Middle East and Europe in the last few months.
While a handful of deaths does not a pandemic make, there is much to fear from tiny imperialistic pathogens—invisible to all but the most powerful microscopes—that invade our cells to replicate, messing them up like a coke-fueled rock band destroys a hotel room after a concert.
All the hand-sanitizer in the world can’t save us from some of history’s nastiest viruses and the horrifying diseases they cause in humans—and we know you’re just itching to know all about them. Here are 9 of the deadliest viruses the world have seen in 21st Century .