In the vampire novel, Unholy Embrace, the vampire that turned me is described as a horrible looking creature whose facial features bear little resemblance to humanity. While some movies and books have depict vampires as strange looking creatures, this cannot be possible. Vampires are made from humans; therefore, they must look like humans. However, there is an exception. This relates to the stories of the "Pure Bloods," which are thousands of years old.
Much material points to Lilith, Adam's first wife, as the source for vampires.
According to a number of sources, Lilith was made the first wife of Adam. These sources claim that Lilith was fashioned from the earth at either the same time as Adam, or before Adam. This made Lilith Adam's equal. Lilith refused to lie on her back while Adam took the dominant position in sex (missionary style). Lilith believed they should make love as equals. Adam was against this, wanting his wife to be submissive, and Lilith left the Garden of Eden rather than comply.
Adam complained to God, who allegedly sent Angels to talk to Lilith telling her to comply. It is reported she refused, and as a result, the Angels killed her children. Lilith sought revenge by taking the form of a serpent who seduced Eve to eat the fruit of knowledge. When Adam and Eve were expelled from the Garden of Eden, Adam endured a period of celibacy as penance. During this time, Lilith was reported to have caused nocturnal emissions from Adam. She collected his semen and impregnated herself with it, giving birth to demons. These children of Lilith called Lilin or Lilim, "night-demons," or the modern term, vampires.
It is my strong belief, that in some fashion, Lilith became the mother of the first vampires, referred to as Pure Bloods, a term found in Ancient Babylonian Tablets. I have not been able to find any sources explaining why Lilith's progeny developed horrible, nonhuman appearances.