Actually, the Black Death didn't disappear. It was a bubonic plague epidemic, and the bubonic plague is still out there. It's a lot more rare, as we know now how to deal with it, but there was an outbreak of it in Madagascar as recently as 1995.
Leprosy also still exists, and is rare now (at least, outside of the third world) because we learned what it was and how to deal with it.
The Sweating Sickness, however, simply vanished. The last reported case of it was in 1551, and although the descriptions written about it WERE very clear and detailed, no one has ever known what it was or what caused it. Some medical historians believe it was some sort of unidentified hantavirus. With nothing to go on but descriptions of the symptoms and progress of the disease, they can't do anything but guess.
I see you like epidemiology, too.
1551, huh? I knew it had to be around then because of Henry being so terrified of it (It killed his brother Arthur, which is why Henry became king, and almost killed Katherine of Aragon) and sending Anne Boleyn away -- and she did get it, but survived. As for Bubonic Plague, of course one of the greatest plagues in history that we've never heard of was the epidemic in India and China in the early 1900s --- killed millions, but who knew? Then it was carried into San Francisco by Chinese illegals in...1906, I think it was. They had quite a little epidemic there and a bunch of people died, mostly Chinese and Mexicans. After that, of course, it got into the California ground squirrels, like the Mongolian marmots that carried it in 1347 to the Crimea. It moved further into Arizona, and it's still endemic; two people a year die of it before they can figure out what they have. It's waiting for the Prepper Apocalypse when it will kill a whole lot of people, I suppose.
The other one I like is the Pericles Disease --- when Pericles decided it was somehow a GOOD idea to pull all the Athenians inside the walls of Athens (430 B.C.), herds and all, while the Spartans laid waste to all their olive trees and grain crops during the early part of the Peloponnesian War. The Plague of Pericles duly ensued, unsurprisingly -- goes to show what government is worth! -- and he died of it, as he deserved (I am not a fan of Pericles), and it was well described by physicians then, but we still don't know what it was. Absolutely everything we know of has been suggested, including Ebola (unlikely!). But it was probably like SARS, here then gone again.
