When using the term "vampire disease", it's important to distinguish between the two different definitions of the term:
Porphyric Hemophilia is a condition caused by a bacterial strain carried in the blood and saliva of every vampire. A human who comes in contact with the blood or saliva of a vampire can easily become exposed to this bacteria. Once exposed, an infected human only has about 72 hours to begin antibiotic treatments before the bacteria becomes incurable.
In essence, this "vampire disease" spreads through the human's body, changing the chemistry of the blood and skin. The first symptoms of infection may include photosensitivity or photodermatitis (sensitivity to light of the eyes or skin). Muscle weakness or seizures can occur, as well as inconsistencies in the nervous system, such as a slow or rapid heartbeat.
Eventually the bacteria behind this disease settles into the body and lives there, creating a perfect environment for it to exist in. At this point, the human body has been completely transformed with the curses, but not the benefits of vampirism. In order to gain immortality, strength, and speed, one must still drink the blood of a vampire.
The term "Sangue Debolezza" comes from Italian, literally
translating to "blood weakness". The origins of this rare vampire
disease remain unknown, but we do know that it only affects vampires.
The symptoms of Sangue Debolezza include severe exhaustion and chronic headaches, followed by nausea, which eventually leads to starvation in many cases.
It is a difficult disease to learn about because only vampires can acquire it, and they rarely subject themselves to medical examination. According to most sources, it is a very rare condition, but it is the only known disease that can kill a vampire.