Vampirism

Vampires that leave corpses are the easy ones to deal with, as with most monsters stupid enough to leave an obvious trail. No, the ones you must watch out for are those like the Ishmael Tenebris of old. Those that live a public life but around whom rumors abound, with narry a shred of evidence as proof.

— Jasper Cameron, Leader of the Bronze Ravens

History

We dont know much about the early days of vampires. We know that Ishmael Tenebris, should you believe the claims, the first ever in this world. Created around the time the Myrdhor Desert was formed, and from similar magics. Vampires have since spread through most of the known world, although the evolution of vampire society is not what we shall be discussing here, rather, we shall be discussing the condition of Vampirism, how it is spread, its upsides, its downsides, and those things in-between.

Transmission

There are at least 2 ways to become a vampire, although there are rumors of another.
The first, and perhaps the best documented, is to be bitten by a vampire. Although popularized the world over, this is in fact the rarer of the ways that new vampires are made. For the vampires made this way are... lesser I think. THey are actually the result of inturrupted feeings. I dont quite understand the mechanism involved, but in a regular feeding vampires do not leave the stereotypical puncture marks that one thinks of, instead the victim is left alive and unharmed, except for the loss of blood. This healing that takes place cleanses the body of whatever would cause the transformation into the vampire.
Vampires created this way are often considered lesser by other vampires. More ruled by their hunger than the second type, they are no doubt the ones responsible for popularized killing sprees. Their blood resivoiurs drain dangerously quickly due to their "half-formed" nature. They also do not mature, as other vampires do, and as such are left with many crippling weaknesses.
The second type of vampire is made by mingling the blood of a mature vampire with one's own. They are often raised and fed through the beginning stages of their new life by the one that turned them, before going on to serve one of the worlds vampire run trading consortiums in some way or another.
The third way is whispered about, but though my research is extensive and my sources vast I have not been able to confirm its existance. For there had to be a first vampire, and they could not have been bitten or had their blood mingled with another. There was a ritual done by the giants of Aranak to turn Ishmael. RUmor has it it was powered by his own soul, offered to an elder being bound in Cysgodol. Should the details of this spell ever be discovered It would be possible for even greater creatures such as dragons and sphinxes to be turned into vampires. And should that happen, may the gods help us all.

Symptoms

Vampirism can, realistically, be considered a warlock pact gone semi-contagious. The benefits and detriments can all be linked back to Kamzaga, a lesser eldritch being bound in Cysgodol.
First and foremost, as with any denizens of the shadow realms, comes sunlight sensitivity. In new vampires this is a lethal affliction, with sunlight burning them away in a matte rof seconds. As a vampire matures this becomes less of an issue, with there being sever recorded instances of Vampire Elders able to basically ignore the damaging effects of the sun for hours at a time.
Similarly, due to their magical nature, once one becomes a vampire you become beholden to the laws for the Fae realms. Running water can strip away protective magics that keep the body functioning. A Threshold can only be crossed by invitation, and Hallowed grown becomes anathema to them.
There is, of course, also the need to drink the blood of others, and the general undead nature that comes with vampirism. Being undead has some benefits, such as increased strength and speed, and no need to sleep or breathe.
All these benefits, as well as access to rather specific magics, such as shapechanging or mind control, can be tapped into by accessing what I have learned is called a blood well. A vampire's blood well is sort of... a magical reservoir contributed to by the vampires feedings but also a portion of the of the well of any vampire they converted is sent to their well. A well is constantly drained by those up the higherarchy, all the way up to Kamzaga, though what use he has for the blood/magic none know.
Should a blood well become too "empty" the vampire is likely to go into a blood rage, attacking nearby living creatures in an attempt to re-fill the well. Sentient or magical creatures are required. Cows and other common livestock, for instance, would be slaughtered but would not allow the vampire to live longer, but a unicorn or cockatrice would potentially satiate the blood rage.
As previously mentioned the lager a blood well's capacity, the more powerful the vampire is. As older vampires typically have more "offspring" to draw from, in addition to their established feeding habits, they tend to be more powerful, but there have been occasions, usually ill fated, where some upstart young vampire has started some cult or another to rapidly grow their power. This attracts attention and if adventurers dont stamp it out, elder vampires usually will.