And as for that, rabies isn't the best pvm skill if you're in 8 player games, so you'll definitely want a backup attack like fury and this is where the plague bearer will show its weakness. Relatively low damage and pretty slow speed.
I have heard that it just adds, but I have also heard that rabies overrides other poison sources, so I don't really know. Worst case scenario, PNova does nothing. Not like an unsynergized low level pnova would do much anyways