S3, E13: A rat infected with a newly engineered virus escapes from the lab when the scientist is murdered, and soon becomes Screed's next meal. Designed to combat HIV, the new virus is a first only mildly harmful to vampires but intensifies with each successive "feeding," quickly becoming lethal. As the virus spreads rapidly through the vampire community, ultimately infecting both Vachon and Lacroix, Nick races against time to find the killer- and hopefully a cure.