Does Warwick w passive not work on the low health enemy jungler?

I was playing Warwick one game and the W passive seemed to work fine on the low health laners but when I walked in the enemy jungle, I saw a pretty low enemy jungler but the W passive didn't hunt him the whole time. Did Riot make it so that W didn't track the enemy jungler because it would be too op or is it just one of Warwick's bugs?