Ok I've only tested this on my lock however it could probably work with any other class considering they can summon a pet. Here are the steps:
1. Get infection in Shattrath
2. Fly to Allerian or Stonebreaker on flying mount (you can use FP if healer is dead)
3. Summon pet
4. When infection is ~30 seconds left take the Flight path to Shatt or wherever you want to wreak havoc.
5. If you followed the above you will turn into a zombie during the flight.
6. Once you land you will have your pet out with you.
7. The pet bar disappears so use your abilities tab to make it attack things like the argent healers (they don't have ranged so pet can kill them pretty easily).
I got inspiration to this from a previous thread that said if u turn into a zombie after dying from fall damage your pet will be out......this did not work for me but up to date this strategy works. It can probably be used in other major cities as well. I use this all the time to destroy shattrath by killing the healers =).
Have fun!