Seriously, post a replay, it's going to get you the most quality advice.
Secondly, have you conisdered consumables? I believe there's one that would remove UB's DoT (I could be wrong though)
I'm probably not playing at anywhere near your level of competition, but usually I find that 1v1 I can force an UB to retreat as Erebus, and although he assumes his spit will finish me off I can typically get the health back by biting full strength creeps.
Also consider having your minions wail on UB while you are running away.
UB will get some damage into you, but not nearly as much as if you were duking it out with him and if you've got enough minion DPS then you should be able to force him to retreat from behind your lines while you are relatively healthy and he is low on health and mana. When playing as Erebus that means you can typically bat swarm after him and chew him up.