Bio-cat virus.

 WARNING, THIS VIRUS IS MORTAL FOR ALL LIVING CREATURES EXCEPT CATS 

Stage 1: Nothing happens for the time being, until after five hours.

Stage 2: After five hours, the infected will start experiencing hallucinations, and they will start to turn deaf.

Stage 3: The infected will start to turn insane and attack anyone they see in the battlefield.

Stage 4: The infected's body will start to rot. Some body parts may fail, and even fall off. They will also become blind.

Stage 5: The infected slips to cardiac arrest.

Stage 6: The cure, literally just water, becomes useless.

Stage 7: The infected's head explodes.

[Virus does not affect cats.]

Virus must be sealed in a glass container, if there is a crack then it will leak out and infect everybody that is not a cat or kitten.

The virus is repelled by hydrogen, which is why the Water Race are immune to it, as well as why it is the cure.