Board Thread:Legitimate Canon Questions/@comment-26110486-20150214234603/@comment-4091815-20150215012443

It's to do with the mental link between Alpha and bitten. It's explained in the Alpha section on the Werewolf page.

As for Jackson, we've seen that a a scratch can transform. Jackson's scratches from Derek were infected with wolfsbane which reacted whenever the Alpha was close enough, like the video store.