[Narvin is fascinated and a little bit perturbed by this virus.]

Does it alter the infected person's memory as well as their appearance? So they believe that they are this other person, when in fact there's merely an...echo?

[Shifting faces is perfectly fine, but altering memories is a frightening thing for a Time Lord since memories are all they have to maintain a consistent identity throughout their many lives. And Narvin, for all his privately-acknowledged faults, would like to keep his own identity.

He's glad to hear that's it's curable at least.]