One important thing with a concealment OP is not to panic. They are designed so they get all of their burst out of their opening shots while they stun you and hit you from behind. Use your self heal and medpac, knock them back, use your slow. Their best moves are melee.
This is what someone else was alluding to earlier. With melee, their leaps are generally outside of 15 meters. So if you can stay at around 10 meters using your slows and stuns and knockbacks, they will spend a lot of time chasing you around while you are hitting them.
Leap is at >= 10m. If rage specced there is a second leap at < 10m. Jugs have also force push so they can reset their leap and the required distance.