Last night, me (naix) and my friend (Phantom Assassin) were against Bristleback on the bottom lane. We tried to take him down multiple times, but every single time we ended up with either me or PA dead while Bristleback walked away with less than 20-30 hp.

I know that Bristleback has reduced damage taken on his back or on the side, so I have been trying to outrun him and right click him from the front. That put me in a lot of danger since it allows him to stack a lot of Quill Spray. It just seems like there's no chance for naix nor PA to take down Bristleback without some form of help from the other guys.

So what is the best way to counter Bristleback ? Which hero or item or strategy is an effective measure against him?