Top 5 Worst Diseases in SF:
5) Drafa Plague - Babylon 5, season 2, "Confessions and Lamentations"
Unlike the Star Trek franchise, deadly diseases were a pretty rare plot device in Babylon 5 - they didn't pop up every three or four episodes as yet another threat to test the wits or toughness of the lead characters. "Confessions and Lamentations" though was one episode where disease did factor hugely into the plot, as it ultimately exterminated the entire Markab race, and threatened several others before a cure was eventually found. Looking back on it, I'm not sure what was more frightening about this disease: the fact that it annihilated an entire species in the span of about a year, or that the Markab probably doomed themselves by refusing to do anything about it or even talk about it because the contagion fell under religious taboo for being associated with those thought to be morally unclean. Clearly there's an allegory for the stigma around AIDS, with some people back in 80's and early 90's (and unfortunately, even still today) wanting to sweep the problem under the rug (or even more horrifically, considering it a punishment from god) because of its association with the gay community (despite its presence among the heterosexual community as well). What's most powerful about this episode though is the clear message that only by reaching out to each other, no matter what community we come from, by helping rather than shunning, do all of us have a chance at survival; that the loss of one community diminishes us all. Looking at the B5 universe, it might be noted that there's another terrible disease that rears its ugly head (and in fact has an entire - if short-lived - series devoted to it): the Shadow Plague/Drakh Plague. Certainly this is a disease that has destroyed other species that have tangled with the Shadows and their minions, and ultimately threatens the population of the Earth. But it's comparatively slow, taking something on the order of 5 years to do its dirty work, as opposed to the Markabs' Drafa Plague, which annihilated that race in about 1 year. With less time to find a cure, I'd be more worried about the Drafa Plague. The only reason it's going at the bottom of the list is because it appears to be a relatively peaceful death.
4) "germs" - The War of the Worlds, by HG Wells
Wells doesn't single out a particular germ to seal the deal for the Martian invaders, rather he uses the plural and goes on to say that all of the bugs that mankind has had to live with, developing immunity or limited resistance to, at the cost of many lives, have combined to attack the extraterrestrials' bodies. It's bad enough (at least if you're a Martian) that they cause a total Martian kill-off in a matter of weeks, but what's worse is that these are real bacteria and viruses that have killed many humans in the past before natural resistance was developed or immunizations discovered. In fact, if we count the many common strains of influenza that were no doubt part of this microscopic defence force, you can't help but remember that thousands of people around the world still die from germs like this every year. Real germs are scary.
3) Xenovirus Takis-A/the Wild Card virus - Wild Cards, edited by George RR Martin
Developed by a race of humanoid aliens to give themselves super powers, it was sent to Earth for testing to ensure safety. Although one of the aliens, who the people of Earth would eventually call Dr Tachyon, stopped the initial attempt to release the virus, the bomb that contained it was captured by a human and released during a battle above New York, spreading across the world on the winds. It was nick-named the Wild Card virus because of the unpredictability of its effects. 90% of those who contract it die horribly when it manifests: they might explode, burst into flame, melt, get ripped apart from the inside out, or suffer a wide range of other gruesome ends. This is referred to as drawing the Black Queen. With the 10% who survive, 9% draw a Joker and are inflicted with deformities. These can range from problems like translucent skin, tails, squid tentacle mustaches, to full transformations into animals, to deformities accompanied by super powers like Peregrin (a woman with wings who can fly) or Troll (changed into a frightening 8-foot troll with super strength and tough skin), to crippling and painful disfigurements that are awful to behold, like Peanut and Snotman. Only 1% of those who contract the virus draw an Ace and manifest super powers. However, only one-tenth of these have abilities that are significant, like super strength, the ability to fly, telekinesis, or invulnerability; the rest are given relatively useless powers, like Rainbow Man (guess what he can do?). Because of the risk of an unexpected, horrible, agonizing death, or being left to survive with a crippling disfigurement, the Wild Card virus easily earns a place in the top 3 of this list.
Admittedly, this is a meta nomination, referring to a condition portrayed in many, many books, movies, and now TV shows. Do zombies result from a disease? Some works have portrayed the outbreaks this way, while others chalk them up to the supernatural or cosmic rays or whatever. Any way you slice it though, the zombie outbreak certainly behaves like a disease, with infected individuals spreading the condition to others through bites, and those who survive the initial eating attack eventually being overcome and transformed into zombies themselves who then prey on other living people. Zombies aren't the only critters from horror who spread like a disease; certainly vampires and werewolves behave the same way, transmitting their condition through bites (more or less). But of the three types of supernatural infectors, zombies have always been the most frightening to me. Sure, being hunted and bitten by a vampire or werewolf is terrifying and painful, and the eventual transformation itself carries the promise of further pain and horror, but at least with these two there's the possibility of retaining some degree of sentience and free will. For all but the most animalistic vampires, after the need to feed is satisfied, there's time to put one's mind to other things and a retention of the sense of self. For the werewolf, it's a once a month trauma, but again, there's the retention of the self and the possibility of leading some kind of life the rest of the time. Admittedly, for both there's the possibility over time of a weight of guilt for atrocities committed, and, in the case of werewolves, the fear of the pain of the next transformation. But zombies, on the other hand, are completely mindless, shuffling, disgusting monsters constantly in search of the next kill, acting either alone or in a mob to drag their screaming victims on them to eat them alive. It's a frightening, painful process becoming one, and once transformed, there's a total loss of self. The zombie disease is also remarkably fast-spreading, with total apocalypse coming very quickly, whereas vampires and werewolves tend to be far more controlled in their spread, having some degree of choice in whether to transform or permanently kill victims, and generally opting to simply kill and feed on them. I don't tend to follow horror too closely, but I don't know of too many stories about total werewolf or vampire apocalypses (aside from Richard Matheson's I Am Legend and its movie adaptations, or Peter Watts' Blindsight). The zombie "disease" certainly is one of the worst in speculative fiction.
1) the Black Death/Bubonic Plague - The Years of Rice and Salt, by Kim Stanley Robinson; Eifelheim, by Michael Flynn
What's worse than a supernatural disease that kills millions? A real one. And one of the scariest in recorded history is the Black Plague. It's estimated that in the mid 14th century this painful, awful disease killed anywhere from 1/3 to 2/3 of Europe's population, and there were further outbreaks over the next 500 years. Eifelheim tells the story of German villagers who discover a starship that's crashed in a nearby forest and who have to learn to live with their new alien neighbours. Eventually, the plague arrives wipes out the entire town. It is a story of how people cope with the introduction of something immensely different, with change, and with their inevitable deaths in the face of a seemingly unstoppable force of nature. In The Years of Rice and Salt, Robinson creates an alternate history where the Black Death goes into overdrive, killing 99% of Europe's population. The story opens with a haunting image of a Mongol warrior riding alone into a European countryside filled with towns but empty of people. It's fascinating to see how Robinson uses the (exaggerated) effect of a real disease to paint a centuries-long history of the development of the rest of the world's cultures free from Western influence (a history that's neither better nor worse than the real world's, merely different, if equally violent). The Black Death is, without question, the worst disease that's been used in SF because it actually happened and because of its terrible death toll.
-the Vidiian Phage - Star Trek Voyager - The Trek franchise presented a lot of diseases over the years, but this one always seemed the creepiest to me.
-Borg nanoprobes - Trek's variation on the zombie theme
-the Cylon-killing disease - new Battlestar Galactica
So which diseases from SF do you think are the worst?