Not Chicken

[EstoPerpetua]

This is not the most well thought through thing I've ever done, it doesn't flow well, the rhyming's mediocre, and it's pretty stupid all things copnsidered, but I thought I'd give you a stab at it, and see if it is as easy as I think it is.

Something of the cow is my enemy,
It was the first of its kind,
but is now one of many.
Although I have all of the bases covered,
I am not alive nor will I ever be,
Though my sole goal is to reproduce.

It is through this process that I do kill,
I kidnap my enemies,
And make them submit to my will.
My mark is clustered around the head, hands, and feet,
And scarred like the moon will you be until
the day that you finally die.

A pity it is that I can no longer hunt,
For you see the rings have stopped me,
And though in prison, nothing can stunt
My inevitable growth and conquering of all men.

I am the greatest killer of all history,
What I am though is the mystery.

What is my name?  

[Kerobian]

Hm, a clever wording.

It is clearly: Some form of viral disease, and my first guesses are Plague and Leprosy. However, those diseases are Bacterial, which leaves still things such as Smallpox, which I think is the answer.  

[EstoPerpetua]

Good guess. You are right!