The "Plagued" affix is a nice idea by itself; however, as soon as a cramped space is infected IT WILL NEVER GO AWAY.
All my pets have it because a enderman teleported into my base, with the plague instantly being spread from entity to entity. The effect disappears after a while, but not if animals keeping touching eachother.
I am not aware of any way of removing this effect on a large scale without cheating.

In my opinion, this is totally broken and I see two solutions:

1. Remove the spreading between entities
2. Only apply the potion effect for the remaining duration (and not at all with 1 second left)

Thank you for coming to my ted talk.

Thanks for the quick response! Great mod overall.