Sleepwalker Virus is believed to be artificial in nature, probably some kind of nanotechnology that is engineered to take over the minds and bodies of their human hosts, turning them into a sleeper agent and/or puppet to the Outsiders.
Humans with an exceptional amount of willpower can fight off the effects of the virus, but will eventually succumb to it. It is possible to help non-hostile sleepwalkers recover from the virus, however.
The Outsiders have contaminated most of US public water supply with this virus, infecting many hundreds, if not thousands of civilians. It is believed that the strange black blob-like creatures known as a Silacoid are created spreading the virus into areas that have their own water supply.
The virus appears to start out as the unsuspecting common cold, but eventually makes way for much more noticeable symptoms: black bile leaking from the eyes, ears, nose, and mouth, unhealthily pale skin, and the infected's eyes turn red.
Sleepwalkers tend to come in two varieties:
Non-hostile: The human host is in a catatonic state, caught in the last moments before the virus took hold.
Hostile: The human host has fully succumbed to the virus, becoming a sleeper agent and puppet to the Outsiders.
Agent Carter's first encounter with a Sleepwalker came in the form of a female Air Force Officer who shot Carter while trying to recover the case he was to deliver to Director Faulke.
It should be noted that the only Sleepwalkers that actively attack are the Air Force Officer and General Deems and this is during the cinematics. During the single player campaign the player is not assaulted by any Sleepwalkers encountered. In the Hanger 6 R&D DLC, it was explained that this particular function of Mosaic was shutdown by Nico DaSilva and Dr. Dresner.
- Lawrence Bailey (briefly, deceased)
- Female Air Force Officer
- General Deems
- Subject 23 - Agent Donovan
- Nico DaSilva (briefly, cured)
- Leon Barnes' son
- Peter Weaver (deceased)
The Sleepwalkers are known to be controlled by Mosaic at first to turn on their own kind, just like the lady Carter encountered at groom range. The Sleepwalkers can only handle Mosaic's control for a little bit, leaving them docile. Carter encountered a Sleepwalker in the Rosement coffee shop during the mission to find Doctor Weir. Many doctors said that the Silicoid substance on their face was what controlling them, acting like a Outsider infantry. Later Carter found out there is a cure for these Sleepwalkers. After multiple medical procedures done by nurse Campbell and Doctor Hara, the Sleepwalker still could not ensure a full recovery. Later on Heinrich and Doctor Hara discovered that a psychological connection is needed to cure these Sleepwalkers. Carter was asked to help talking DaSilva out of the Sleepwalker infection. It is said to be like a child in a dreamworld. After Carter did that, there was said to be a cure, but the patients still required lots of medical attention. If the game is finished with Dr. Weir, he will find a full cure for the Sleepwalkers. Luckily, they don't remember anything upon awakening.