Upon a pale horse... (The Mists of Ravenloft)
Lycanthrope plague created by Jacqueline Reiner and her filth priests in which those bitten by infected common rats would contract lycanthrope and become wererats under her control. It is believed that the Sisters War was nothing more than a cover to infect as much of the population as possible, in the shortest amount of time.
Creation and discovery
An early version of the plague was discovered as a serum uncovered by Dr. Evan Moreau in the sewers beneath Mortigny, along with a number of secrets on wererat society. This version of the serum was completely unstable and turned the people injected with it into uncontrollable wererat abominations, as well as quickly killing any common rats it was injected with.
A critical section of the notes found with the serum read as follows:
The various modified progenitor samples have met with limited success. When the contagion levels are positive, the strain has proven too lethal or deconstructive to either the subject or the vector.
The most promising sample is (unsurprisingly) from the R-strain. Specifically R-21B, which, though nearly identical, exhibits slight structural differences from the others in the R-strain. It is in this sample that I believe that a breakthrough is imminent, and thus the remainder of the work should be focused.