The Virus

"It is not a regular virus, it's a weapons-grade strain engineered to achieve maximum lethality within a short time and then turn harmless."

- A Doctor talking to a Ranger officer about the virus.

The Virus is an experimental biological weapon based on the Ebola virus, and is featured in Metro: Last Light. It's stolen from D6 by the Red Line sleeper agent, Lesnitsky. The Red Army is planning to use it against the entire Metro, to wipe out the Nazis, Rangers, Hansa, and the other major factions of the metro.

Overview
In real life, the Ebola virus is a serious and very virulent disease first found in the jungles of the Congo. The disease is classified as a level 4 biological hazard and, as such, is one of the most deadly diseases in the world. Once infected, the virus attacks the cell lining of the patients blood capillaries. Once degraded, movement of any kind, even breathing and blood flow, is enough to burst the capillaries, causing insurmountable hemorrhaging (bleeding) in any (and frequently most) body parts. You can read more about it here.

The virus is a particularly deadly strain of Ebola, and was biochemically engineered to have a incubation period of a matter of hours, killing those afflicted within two days. The virus also has a mortality rate of 95%, possibly modified to be spread via aerosol and be virulent for only two days after being released into the air; after which, it will go inert and will eventually die down, preventing further infection. This makes it particularly effective for biological warfare, as it has an extremely high mortality rate (surpassing even the deadliest naturally occurring strains of the Ebola virus), kills very quickly, and theoretically doesn't linger long enough to create a lasting pestilence for an invading army.

In the game, this virus has no visible form, other than the test tubes that are found during several cutscenes. During "Quarantine", the player will see many individuals that have been exposed to this virus, and are either very sick, immobile, or dead. While the virus is contagious, and the Red Line has gone so far as to kill infected innocents in order to quicken the dissipation of it. Artyom can't be harmed by it - especially while wearing a gas mask. Although the virus is a major part of the story, the Red Army's plan of using it against the entire metro fails in both endings.

Hints
The virus plays a serious role in the game, though its existence is not revealed until late in the game - however, there are numerous clues that can be heard by Artyom before this:
 * Korbut
 * After Artyom's interrogation and escape, he can listen in on a conversation between Comrade Moskvin and General Korbut. In it, Korbut mentions that he has a special "trick" that will allow him to seize the metro without any bloodshed. Moskvin is dismissive, but authorizes Korbut's plans.
 * Revolution
 * In the loading screen, Artyom ponders about the item from D6, stolen by Lesnitsky.
 * During this chapter, Artyom will find several clues about the virus.
 * Venice
 * ​While listening at the door of the brothel, Pavel is the first to openly speak of the virus.
 * In the storage facility, two bandits are talking about a locked parcel filled with "flyers for the working people" that was sent to Oktyabrskaya.
 * Contagion
 * One of the major levels in which the virus is found. At the beginning, the player can hear citizens being executed by the Reds for suspected infection.
 * If the player manages to quickly take down the two Reds that were executing the citizens, a close to death citizen will tell Artyom that the Reds came with the flamers before hardly anybody died of the virus. This explains to Artyom that the Reds were behind it, and is a major turning point in the game. Listening to the citizen will award the player with a positive Moral Point.

Trivia
Вирус_Эбола
 * As of 2013, there have been exactly 2 Ebola cases in Russia, both infectees being laboratory workers who accidentally infected themselves via syringe needles during experiments on lab animals, and both cases being fatal.
 * Even the most deadly confirmed real world strains of Ebola (such as the Zaire strain) pale in comparison to this one. It has a stunningly fast incubation period of days or even hours where "normal" strains take 1-2 weeks for symptoms to show, a 95% mortality rate whereas even the Zaire strain is on average a 83% mortality rate, it kills in 1-2 days after symptoms present rather than around 7 for Zaire and most critically it may possibly be spread by aerosol; a characteristic which no real world strain has been confirmed to posses. Interestingly, it appears to have been engineered with a kill switch of sorts which cuts the virus' mortality rate sharply 3 or more days after it is initially deployed. This, theoretically, allows it to be used in a more tactical manner than other biological warfare agents such as anthrax, which can persist for years or even decades after being deployed.