Lesser Contagion says your triggering card "also targets the closest ally of that target. If there is more than one such ally, target all of them." My Priest, Warrior, and Wizard were standing in a line with the Warrior in the middle. My Priest cast Righteous Frenzy on my Warrior. It should have spread to everyone, but only my Priest got a copy of the attachment, not my Wizard.
You sure this isn't referring to the type of ally so you can say curse 10 goblin avengers at the same time just my thought on it?