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Kharaa (IPA: /kəˈɹ̠ʷaː/) is an alien bacterium discovered by the Architects 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 waterborne bacteria. 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.

The disease ravaged life on Planet 4546B prior to the hatching and release of five Sea Emperor Leviathan Juveniles.


Kharaa was brought to 4546B by the Architects in an attempt to find a vaccine, as they had established outposts within The Crater. It is stated in Architect data that the Kharaa bacterium has killed over 143 billion individuals over the course of time since its discovery, but the data is likely to be around 1000 years old. 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 behavior and genetic corruption. This prompted the Architects 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, which causes alterations to the body structure, eventually leading to a total shutdown of the organism due to its inability to keep functioning properly. According to Architect 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. They will attempt to kill infected fauna to control the spread of the bacterium.[1] This seems to be ineffective as Kharaa still ravages the planet around one thousand years after it was initially released.

After crash-landing on 4546B, 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 disable 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.

Roughly 5% of all fauna on Planet 4546B can be observed with visible symptoms of the disease. Some creatures do not show any visible symptoms at all, including all leviathans.

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 has 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. The Sea Emperor Leviathan is the only living life form known to have a natural immunity to Kharaa, though several large fauna species apparently possessed a resistance to the disease also, suggesting that they may have produced digestive enzymes related to Enzyme 42. Peepers are able to use the Alien Vents to take small amounts of Enzyme 42 to the surface, spreading the enzyme's effects throughout the world. This method is the sole reason why Ryley, and some creatures by extent, are able to survive some time after being initially infected.

The planetary quarantine remained active until being shut down by Ryley Robinson during the events of Subnautica, who disabled the Quarantine Enforcement Platform after releasing the Sea Emperor Leviathan Juveniles who then began to produce the cure to the Kharaa and spread it across the planet.


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.


The only known cure is Enzyme 42, which is only effectively 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 Architects were unable to find the potent variant of Enzyme 42 and died due to the lack of vaccination or a cure. Ryley Robinson however, was able to obtain 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.

In-game mechanics[]

The infection progresses by certain events, not time.

  • 0.0f = Not Infected/cured = Vital signs normal, continuing to monitor/No remaining signs of bacterial infection
  • 0.25f = Level 1 Infection = Vital signs normal, detecting trace amounts of bacteria
  • 0.50f = Level 2 Infection = Statistically significant levels, be vigilant for symptoms
  • 0.75f = Level 3 Infection = Infection is progressing, skin irritation & immune response
  • 1.0f = Level 4 Infection = Infection has spread to skin and pulmonary system, imperative to neutralize, pustule cutscene triggered

Things that result in infection:

Additional information:

  • Infection Triggers are not cumulative. Entering a the Aurora and then the Mountains will not combine to set you to 1.0f. You will simply progress to that level of infection if you are below it. Most of the triggers are just storyline fail-safes.
  • Warpers only begin inspecting the player at an infection of 0.33f, which would suggest that the player is still safe from Warpers for the first level of infection, meaning that with careful planning, it is possible to complete almost the entire game without worrying about Warpers.
  • Enzyme Host Peepers (HeroPeeper) carry the enzyme that can inhibit the effects of the infection. Enzyme Host Peepers do in fact cure infected creatures - and will actively attempt to do so if they see an infected creature while swimming.
  • The player can cure an infected creature by feeding it a Enzyme Host Peeper from their hand. This may take more than one Enzyme Host Peeper - each heals 0.5f of infection, while the infection value is set to 1.0f when InfectCreature() is called. This only works on creatures - the player must cure themselves through the storyline or console commands.
  • Enzyme Host Peepers are made and born. If a Peeper spawns outside of the Safe Shallows, it has a 5% chance of being an Enzyme Host (BornHero), but you can make any Peeper an Enzyme Host (BecomeHero) by releasing it near an Alien Vent. The enzyme depletes over time, but a BornHero Peeper has the ability to regenerate its enzyme.
  • There is another variant of Peeper for peeper.isInPrisonAquarium, which has its own PDA entry - this is specific to Peepers in the Primary Containment Facility.
  • Additionally, a cured creature can be scanned, unlocking a PDA entry.
  • In an aquarium, fish will infect each other if one infected creature is present and an Enzyme Host Peeper is not. If at least one Enzyme Host is present, all fish will be cured and the infection will cease to spread.
  • In Alien Containment Units, Enzyme Host Peepers retain the same HealingTrigger as they would in the wild, except it doesn't deplete.
  • Creatures scan for Enzyme Host Peepers, and will swim towards it if they see it.

Data Bank Entries[]


You have been infected with a previously unknown, waterborne bacterium. It is currently multiplying in your bloodstream. Estimated incubation time: 2 weeks.

Your immune system is currently combating the infection at low efficiency. You may already be experiencing flu-like symptoms and skin irritation. These will likely be exacerbated as the bacterium takes hold.

Your immediate priority should be abatement and eradication of the infection.

Recommended steps:
- Salvage further alien research data on a possible vaccine
- Investigate the mechanisms which have enabled the indigenous ecosystem to inhibit the symptoms of the infection

Discovery: First encountered during routine network expansion on outer worlds.

Pandemic Development: Network error resulted in routine quarantine procedure failure. Contagion was uploaded to, and spread quickly through, the core worlds. Confirmed deaths: 143 billion individuals.

Bacterial Mechanisms: Attaches to healthy living cells and mutates the basic genetic structure.

Symptoms: Stage 1: None. Stage 2: Gradual immune system failure. Stage 3: Unpredictable alterations to biological structure. Stage 4: Complete shutdown of executive function.

Emergency Steps Taken: Core worlds quarantined. Bacterial samples distributed to isolated disease research facilities for vaccine development.

Treatment procedure: Unknown.


This organism is displaying signs of a bacterial infection.

- Bright green blisters are forming networks around the infection sites
- Pathology suggests a waterborne bacterium capable of penetrating the body through the skin and respiratory system
- Underlying indications of genetic mutation and aggressive behavior
- The bacterium itself is unlike any so far recorded in human exploration

WARNING: May be contagious. Avoid. Do not under any circumstances consume the flesh.

Scans indicate this infected organism has recently come into contact with a unique enzyme which has counteracted the most debilitating symptoms of its infection.

- Skin blistering has rapidly receded and been replaced with healthy tissue
- Altered genetic material has been replaced with original DNA from remaining healthy cells
- Behavior normal
- The bacteria is still present in the bloodstream, but is currently dormant

Assessment: Investigate enzyme origin



  • 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 Architects.
  • The former name for Kharaa Bacterium was Carar Bacterium. It was later changed to match Natural Selection 2.
  • In the early stages of development, an Older Version of the Kharaa Bacterium was seen in the game, in which the pustules were orange and more 2D than in the final game. This was likely to match Natural Selection 2's Kharaa Bacterium, which appears as orange.
  • In Mongolian, Kharaa means "Curse / to curse (in Mongolian letters: хараал).
  • Kharaa seems to be inspired by the common disease of Swimmer's Itch, as they both cause severe skin irritation and the appearance of small blisters.


  1. Dated August 26th, 2016.