Some stuff I thought were related to my previous post: The second most amazing disease I've encountered so far is the Plague. The mechanism of transmission, and the circumstances that lead to finding it are also amazing. From the wiki page:
It is mainly a disease in the fleas that infested the rats, making the rats themselves the first victims of the plague. Infection in a human occurs when a person is bitten by a flea that has been infected by biting a rodent that itself has been infected by the bite of a flea carrying the disease. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve. The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound. The bubonic plague bacterium then infects a new victim, and the flea eventually dies from starvation.
As an aside, one of the classic 'punishment births' in Indian mythology is a preta, a state defined by voracious, unsatisfiable hunger.
Easily the most mind-numbing disease I've read about is Syphilis. [You can wiki it, but the page contains graphic images of diseased penises. I suggest you disable images and then load it if you are not sure]. Here's a paraphrased, simplified and dramatized version of the diseases's effects: The victim gets the bacteria via sexual contact. In a few days, a few small, painless boils appear near the point of contact and elsewhere. In most cases, they are hard to even find. They go away without any incident in a few weeks. Nothing happens for the next few months. Then, lesions appear throughout the body and go away without incident again in a few weeks. In most of cases, people don't even bother to visit doctors because the symptoms are not debilitating in any way. Even if they do go to a doctor, it is very hard to diagnose because the symptoms are extremely commonplace and similar to tens of other simpler diseases. It's for this reason that Syphilis is called 'the great imitator'.
Next, the disease waits for as much as 30 years before manifesting itself seriously! This stage is precipitous, and many large organ systems fail at the same time, including drastic changes in the victim's personality itself. Imagine that! 30 years!
Another reason why Syphilis is amazing is the history of cures people have attempted for it. One of them was mercury fumigation, and here is another one of those all-time-epic articles about mercury: The magical properties of Mercury.