Kharaa Bacterium
The Virus is an affliction that seems to be all over Planet 4546B. It is described in the Degasi PDAs to be "part of the ecosystem".
Afflicted creatures will be identifiable by the small, glowing cysts on their body.[1]
Warpers will attack infected creatures once their infection passes a certain level.[2]
The player will become infected with the Virus at a certain point in the story.