[@Lurking Shadow]
Feral as in completely inhuman. Nothing left but the desire to feed, at all costs, is my understanding.

I would assume the onslaught of deformities beginning and / or the loss of cognitive control, a kind of cognitive dissonance if you will, would be what would alert one to the onset of the Infection. Add in the increase in speed and strength in parallel to the rate of Infection...

Though Sarafine could, for fact, tell you. Assuming she cared enough to and was around your character. Which I intend for all PCs to bet with Sarafine over the course of a few weeks.