Another cracking episode.

I think the reason Tanya was freaking out is that she has been bitten or infected some other way, when I don't know, perhaps recently, perhaps ages ago, but she is immune to it, and fearing that people will freak out and kill her or at the least kick her out she hasn't told anyone, but this will be discovered in the medical, so has decided to do a runner.

Seems like the only logical theory, flash back to the colony....I don't think so, seems far too much of an over reaction. She has only started freaking out when it's made clear that she is going to be physically checked out, she didn't mind too much being kept in a barracks (I assume under lock and key) for the time being.