Prion

Viral and infectious, 

I'm Not quite alive.

I am a prion,

a complex ion,

living to survive.

A diseased agent.

Multiplying rna.

I am a protein,

so very extreme,

cattle one of my pray.

Polyadenylic acid and Creutzfeldt–Jakob disease,

bringing human and bovine to their knees.

Driving them crazy.

Making them mad.

The ultimate definition of bad.

Subject to natural selection and mutation

and other forms of replication.

A long evolutionary stay.

Since the dawn of creation

and subsequent classification,

protein inheritance my way.

I am a prion,

the molecular lion,

rained down on mother nature's parade.

Dressed like a virus.

Old like paper of papyrus

your brain someday I may invade.