Kharaa Bacterium

Kharaa is an alien bacterium discovered by the Precursor Race during the exploration of an unknown planet. It seems to have completely taken over Planet 4546B. It is described in the Degasi PDAs as "part of the ecosystem", with further statements that the Degasi survivors were infected at some point - as stated by Bart Torgal while discussing the flu-like symptoms the crew was experiencing. Early on, the player's PDA and Lifepod will make note of the high levels of bacterial infection in the water. The PDA notes that Kharaa is unlike any infection thus discovered in human history, suggesting that Kharaa's biological design is far more drastic compared to diseases such as Yersinia pestis.

Overview
Kharaa was brought to 4546B by the Precursors to attempt to find a vaccine, as they had established outposts within The Crater. It is stated in Precursor data that the Kharaa bacterium has killed over 143 billion individuals over the course of time since its discovery. It is possible this is not the true death count as the PDA entry only lists these as "Confirmed Deaths" which could imply further dead beyond what was known. Their core worlds were quarantined off, and research facilities such as the one on 4546B were created to find a cure. After a Sea Dragon Leviathan damaged the Disease Research Facility in an attempt to retrieve its offspring, the previously contained Kharaa bacterium was released 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. This prompted the Precursors to initiate their emergency quarantine: activating the Quarantine Enforcement Platform. The Quarantine Enforcement Platform shoots down all approaching or departing spacecraft to prevent Kharaa being spread to other planets.

The PDA estimates that Kharaa incubates in two weeks and quickly kills its host after it reaches a substantial infection level. It accomplishes this by shutting down the immune system (already making the infected host susceptible to other diseases) and causing genetic mutation to the host's DNA, and causing alterations to the body structure, eventually leading to a total shutdown of the organism due to its inability to keep functioning properly. According to Precursor data, the bacterium is capable of entering the body through the skin, and causes an increase in aggression in its host.

Warpers were created to keep the levels of Kharaa to a minimum, to do so they will attempt to kill infected fauna, in an effort to control the spread of the bacterium. This however seems to have been ineffective as Kharaa is still ravaging the planet around one thousand years after it was initially released.

Ryley Robinson is infected with Kharaa, though he only becomes aware of it after attempting to disable the Quarantine Enforcement Platform, as the deactivation terminal will tell him that he is infected and therefore cannot use it, thus forcing Ryley to secure a cure in order to leave the planet. The infection only becomes noticeable when Ryley reaches the Disease Research Facility and is prompted by the PDA to perform a self-scan. At this point it will warn him that the infection is reaching a critical stage and his skin breaks out into glowing green cysts. The same happens to Medical Officer Danby in Lifepod 12. However, unlike Ryley, Danby developed visible signs of infection within three hours. The reason for this is unknown, although the infection rate most likely varies depending on the individual. However, it is also possible that since Ryley had been exposed to the unstable variation of Enzyme 42 for prolonged periods of time, it slowed his progression, whereas Danby was not, and Kharaa quickly spread throughout his system.

The Degasi survivors were also infected at one point. Bart Torgal attempted to find out what it was, although he was unsuccessful as Marguerit continually brought specimens for him to study near death or injected them with Transfuser serums, making them unreliable test subjects. However, he was able to deduce that every organism was infected, as well as taking precautions to ensure the Degasi crew's survival. However, upon the destruction of the Deep Grand Reef base, Bart fled to the Safe Shallows and began noting the details of Kharaa on him, and eventually flees to the Floating Island, where he makes his final log and most likely succumbs to the bacterium.

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 gameplay.

The player can scan fauna that have been scanned previously to check if they are infected with Kharaa. When scanned, a creature can be identified as infected or not by the screen on the Scanner saying "normal" or "infected". The player can also scan themselves to monitor the bacterium's progress in their body.

It seems that the only way to cure Kharaa is with Enzyme 42 produced by the Sea Emperor Leviathan and its young, as shall be shown by creatures being cured by the enzymes in the Sea Emperor's aquarium.

Peepers are able to use the Alien Vents to take small amounts of Enzyme 42 back to the surface, spreading the enzyme's effects throughout the world. This method is the sole reason why some life has managed to remain immune, and possibly why Ryley, and some creatures by extent, are able to survive some time after being initially infected.

The Sea Emperor Leviathan is the only living life form known to have a natural resistance to Kharaa.

Appearance
Kharaa manifests itself in bright green cysts, along with similar colored veins spread throughout its host. The cysts start out as small protrusions, however, as time goes on, the cysts will grow larger and glow more strongly, signifying the organism is close to death.

Cure
The only known cure is Enzyme 42, which is only produced by juvenile Sea Emperor Leviathans. The Enzyme acts as a countermeasure to the bacterium, nullifying its effects and eventually purging it from the body. However, only juveniles can produce this, as the adult Sea Emperor Leviathan's health had deteriorated to the point that its enzymes were not stable for a permanent cure, although it allowed for temporary remission of symptoms. The Precursors were unable to get the variant of Enzyme 42, and died due to the lack of vaccination. Ryley Robinson however, was able to get it with the help of the sole adult Sea Emperor Leviathan, making him the only known individual to achieve a successful cure.

Whether Enzyme 42 works on the variant of Kharaa seen in Natural Selection 2 is unknown.

Data Bank Entries
Bacterial Infection Report=

Kharaa Contagion Profile=

Specimen with Symptoms of Infection=

Specimen with Symptoms of Infection Inhibited=

Gallery
In Game View=

Trivia

 * Cory Strader and Tom Jubert have said that Kharaa from Natural Selection 2 is a mutated form of the Kharaa in Subnautica.
 * The texture of Kharaa's cysts on the player is limited to the hands, since they are the only places with visible skin on the player.
 * In an earlier story script, the Kharaa was a bacterium developed by the Precursors.
 * Despite symptoms of Kharaa occurring after a few weeks of contracting it, Danby managed to develop cysts within a few hours of infection.
 * The former name for Kharaa Bacterium was Carar Bacterium. It was later changed to match Natural Selection 2.
 * In Mongolian, Kharaa means "Curse / to curse."
 * Kharaa seems like a spinoff to the common disease of swimmer's itch, as they both cause severe skin irritation, and the appearance of small blisters.