Explain plague damage effect

What exactly is plague damage doing? If you fill the bar, it is neither a dot nor some kind of movement impairment, even though the helmet affix with more plague damage would suggest a form of damage.

I’m pretty sure if you hit a plagued enemy, they take more damage.
Also they heal less, tho it’s more a problem if you are the one being plagued, most mobs don’t heal.

Thanks…mobs and bosses can heal in pestilence 4 corruption 10…they often get lifesteal and sometimes lifereg