Red Moon Rising by Billie Sue Mosiman

"There exists a rare blood disease that is fatal to most humans. The illness turns a person into a monster with distorted facial features and leaves the victims in excruciating pain. Thankfully their life span is short. In a statistically insignificant part of the population, a gene turns some individuals into vampires upon their death. That particular gene is dominant leading to whole families of vampires, but each clan differs on their approach to human contact. One clan, the Predators sees mankind as a food source while another The Craven prefers to hide in the depressing darkness away from people. The Naturals live among humans drinking their blood sold to them by Predators who own a blood bank.

High school senior Dell Cambien falls for Ryan just before she undergoes the change. Ryan struggles to control her new abilities as she chooses the path her life will take, which might include Dell shaking the foundation of vampirism to its core." (summary from Harriet Klausner at Amazon.com)

Paperback Info: ISBN 0886779553, Daw Books, 2001