Looks like you are playing a 4e game judging by the books you posted, so that Link Sendaz gave you doesn't really apply (that is for 5e).
If I remember right (and I probably do not) There is no way for an infected to increase their magic rating in 4e with Essence drained.
And a quick piece of advice, check with your GM if he will even allow an infected in the group, as they have been known to create... tension. (If he says yes, you're good to go...)