Parasitic

Oddly,  emotions and mental states have "life" to them.  Though not organisms by definition, they seem to live and breathe and grow and evolve.  They also have their own sources of nutrition, the antecedents upon which they feed.  And, to stretch the analogy, emotions and mental states seem also to have the ability to propagate, to beget similar offspring.  

Some emotions and mindsets even take on a parasitic nature.  Anger is like a parasite, if you think about it.  So is hate.  So is distrust.  They need a host, which they slowly but surely invade and permeate.  

Then they destroy their host.

Unless, of course, the host purges them first.