Heavens Demons

600 bc Rome, Italy. Rome fell into a deep depression as a virus spread rapidly through the large city. King Arthur and his round table stood tall till Sir Gawain got a mutation of the virus. It didn't kill him like much of the others, rather turned him immortal. Slowly his body grew out of the disease. But he was left with sharp teeth and a lust for blood.
This mutation began to spread rapidly much like the first strand. People everywhere began to shift and malform into monsters. Some learned to control their new found cravings, others let it consume them.
Present day, the descendants of those who got this mutation still carry the same new and unbelievable traits: enhanced speed, strong senses, enhanced strength, immortality, and a sick craving for blood. They are called lamias or their more recognizable name, vampires.