I've had a few dwarves decide to bite werebeasts, and never seen any of them get infected. It appears that the contagion is in the werebeast's saliva, not it's blood.
I started a new fort, embarking with unskilled dwarves with only a pick and some animals. I refuse to believe you can cut down a tree with a wooden axe, so it was a relief to finally have the caravan arrive so I could get an axe and be able to get some wood. Just in time, too, my mason is in the hospital with a compound fracture of one of his toes, and I was starting to get spammed with "can't give water: no bucket".
As the merchants were leaving, i got an announcement of somebody found, dead. I was surprised to see that it was a merchant, not one of mine, but also a bit concerned. I found his corpse at the top of a tree. I decided I'd best cut the tree down to retrieve the corpse, and when I started going down the tree to find it's trunk (it's a pretty thick forest), right below him I found another corpse, this one identified as just "Udesushen's corpse". Looking at it told me nothing more than that it was Udesushen's corpse. :-/
Looking at the Dead/Missing list, revealed that it was a black bear. Looking back at the combat logs, I found the fight between the bear and the merchant. The bear did a lot of biting and shaking and opening arteries, and it was pretty clear that the merchant had no chance from the start, but right near the end, this happened:
The Merchant bites the black bear in the throat, tearing the skin!
A major artery has been opened by the attack!
He ripped out a bear's carotid artery with his teeth!
Shortly after that, the merchant bled out from the wide variety of wounds the bear had inflicted, but he got his revenge, and the bear didn't even live long enough to climb out of the tree.
Now I just hope neither of their corpses lands on my woodcutter when he cuts the tree down.