Vampirism a disease which affects sapient non-Undead mammals - Humans, Elves, Orcs, Dwarves, Gnomes, Halflings, Goblins, Ogres. The main symptoms are becoming undead, as well as being forced to adopt a nocturnal lifestyle and a diet of mammal blood.
Vampires - along with therianthropes - differ from other forms of undead by the fact that they have preserved their mortal bodies relatively intact. Another trait they have in common with lycantropes - and liches - is their preservation of sentience.
For vampires, the blood of warm-bodied animals - chiefly mammals - is a requirement to sustain their mortal looks, as well as several mortal functions. A well-fed vampire is physically indistinguishable from a mortal: he or she has a warm body warmed up by the stolen blood, regenerates fast when wounded, is capable of sexually reproducing, and can also apreciate the taste of mortal food, albeit not enjoying any benefits from it. When a mortal is turned into a vampire before reaching physical maturity, the vampire will continue to age and grow until reaching said maturity - provided that said vampire is also well-fed. When deprived of blood, this development grinds to a halt.
Other negative consequences of blood-deprivation include an inability to blend into mortal society, a highly unnatural eye colour, lack of regeneration, body entering a state of decay (effectively turning the vampire into something little more than a zombie who is capable of talking - a decaying corpse that walks and talks), and an inability to reproduce sexually, or enjoy the taste of mortal food. Any pregnant vampire's child who is deprived of blood from a prolonged period of time is aborted.
Young vampires are highly averse to the sun - effectively burning to death upon direct contact with sunlight -, and only gain immunity towards it gradually over the course of three centuries. While being satiated with blood gives younger-than-300 vampires temporary resistance to the sun, recklessly going out to the sun will drain them and make them require more blood.
It is important to mention that while vampires are physically not as diverse as lycantropes - which are divided into werewolves, werebears, wereboars, werelions, weretigers, wererats -, they still come in a variety of unique bloodlines with their own attributes and abilities. For example, there is a clan of vampires that doesn't age even when embraced before reaching maturity, is rendered sterile and asexual upon the embrace, but gain tremendous advantages in the arts of magic.
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