Kharaa Bacterium

The Carar is a type of bacterium that seems to have completely taken over Planet 4546B. It is described in the Degasi PDAs as "part of the ecosystem", with further suggestions that the Degasi survivors were infected at some point - as stated by Bart Torgal while discussing the flu-like symptoms the crew was experiencing.

It is stated in the Precursor data that the Carar bacterium has killed over 143 billion creatures over the course of time since its discovery. The bacterium was released after a Sea Dragon Leviathan escaped from the Secondary Bio-Research Facility, resulting in the base's destruction and the release of the previously contained Carar bacterium onto the planet. This decimated the planet's ecosystems, as much of the life on the planet died due to the bacterium's immuno-repressive behaviour and genetic corruption. It is suggested by the PDA that the Carar incubates in two weeks and kills in five weeks - it apparently acomplishes this by shutting down the immune system (already making the infected host susceptible to other diseases) and causing genetic damage to the host's DNA, eventually leading to a total shut-down of the organism due to its inability to keep functioning properly.

Afflicted creatures will be identifiable by the small, glowing cysts on their body.^[1]

Warpers will attempt to kill infected fauna once their infection passes a certain level, in an effort to contain the further spread of the bacterium.^[2]

The player is infected with the Carar, though it only becomes noticeable when the player reaches the Secondary Bio-Research Facility. There is a scanner in the Precursor Ground-To-Air Weapon System that prevents access to the control room if the life form is infected, forcing the player to follow the story and secure a cure.

If an infected creature is placed inside an Aquarium or Alien Containment, the creature will infect the rest of the creatures inside soon after. However, this is purely cosmetic and has no impact on the gameplay.

It seems that the only way to cure Carar is with enzymes produced by the Sea Emperor and its young, as shall be shown by creatures being cured by the enzymes in the Sea Emperor's aquarium.

The Sea Emperor and the Warper are immune to the Carar bacterium, as they both play a role in eliminating it, with the Sea Emperor producing the Enyzme 42 as a countermeasure, and the Warper being the result of its biomechanical adaptations implemented by the Precursors.

Trivia

The way that Carar manifests itself is loosely based off the appearances of the Kharaa from Natural Selection 2, as the Kharaa have similar looking cysts on their body - a "secret" data-log further supports this by explicitly naming the Kharaa and the fight against them as happens in Natural Selection 2.
The texture of the Carar on the player will be limited only to the hands, since these are the only limbs visible.