No. Werewolves do not exist, fortunately, or else we'd be overrun by ravening, outrageously strong beasts that transfer their disease with a scratch or a bite. Consider the spread of aids - and then realize how rapidly such attacks would spread such a thing.
The concept of the werewolf is the medieval/ancient explanation for those who contract rabies, and similar diseases. Alternatively, it can also be viewed as a spiritual exploration of the animalistic nature of aspects of one's spirit.