So one minute it's Ebola, then the next it's Super Ebola/Marburg fusion that ravages everything it comes into contact with.
What next, Rot-Loj-i becomes airborne (That would just be, instantaneous death for everything)?
That would also make vaccines utterly useless, if strains change by the minute, even by the day.
I would love to have a slow working but surely fatal disease or say, diseases or parasites that work in your favor. Like say there's a parasite that attaches itself inside of your body, and it feeds off your magical essence but at the same time it secretes these hormones that improve your other aspects, like sight, strength, agility and so on. Or it could be the other way around, feeding off you physically but gives you great magical abilities (This would reduce your life span). It would also be nice to have Risk/reward situations. Where at certain times in the Rp that you create a event, a player could accept or not accept this, and according to what they did would either make it react negatively or positively later in the rp (just a thought).
Maybe for example, say a human can drink the blood of the four major races to temporary take on the aspects of that race. Makes them stronger, gives them all or some of the abilities of that race.
But now, say it's extremely hard to get the blood of the races, and it probably can be considered a crime if they murder to get the blood, but if races maybe donate the blood it's fine (you would have to provide a service for them). Now say, the blood also happens to be quite addictive, and it takes more blood each time to be able to gain the powers of that race, and without the blood you go into an extreme withdrawal and depending on the amount of the blood you have taken would either kill or weaken you until the time it is completely out of your system.