Commonly called N4 or Nerotonin Type 4, the artificially engineered virus which caused most of the world's population to turn into zombie-like beings or even mutants has had various effects of scientific and practical interest.
While there are no known remains of detailed plans about what Nerotonin 3 was exactly supposed to be capable of, nor are there any details of what exactly turned the prototypes of Nerotonin 3 into a virus totally unlike Nerotonin Type 2, various survivors have observed and learned from the hordes of infected over the years and noted a confirmed list of virus effects.
Out of the base virus that was spread via the primary infections, which already eradicated most of the civilized world, several different strains evolved and spread among the infected.
The various mutated virus strains which appeared over time all have some differing effects, although all viruses retain part of the core virus and most of its effects. The typical infected seen in the Inner City is controlled by a version of the virus which causes several different mutations to the virus host and thus produces the known zombie types of differing danger and strength.
It has recently been discovered, that due to the rapid evolution of the virus, the DNA of many strains of N-4 codes for proteins capable of incorporating various non-essential amino acids during protein synthesis. This helps explain the drastic mutations found in the infected.
Since this document is written from a scientifically neutral point of view, the listed effects may or may not be positive for humanity itself, as they are written from the virus host's point of view, whether it is a normal human survivor, one of the many "zombies" in the Inner City or even animals and other beings which were found to survive an infection - meaning that the virus does not totally destroy one's nervous system but keeps the body alive and working, although usually under its own control.
- Anomalous Growth of Bones, Muscles and the related parts of the nervous system
- Diminished sensitivity to pain from physical damage to the body
- Improved and accelerated regenerative effects
- Increased hearing, sight, and tactile perception capabilities, as well as a highly sensitive sense of smell
- Discoloration or Re-colorization of the skin, depending on how long the mutation has spread
- They do NOT respond to light changes.
The N4 virus also seems to make their host highly resistant to radiation. Not only that, radiation seems to hinder the mutation of the body. The existence of current Irradiated Zombies proved that radiation actually locks zombies in their present state, and permanently halts any further mutation. Scientists in Nastya's Holdout and the other Outposts have begun looking into this phenomenon as a possible way to cure (or at least suppress) N4 infection and mutation, although their progress thus far has been inconclusive.
- Extreme aggression toward non-horde beings (humans, animals, etc.).
- Inability to recall emotional relationships, previous needs, memories as a human, etc.
- Extreme craving for the flesh of uninfected humans (living or dead).
- A mental pull towards being in a horde (hive/mob mentality).
- In the (alleged) N5 cases only: The ability to complete complex thought and construction of structures.
- Only capable of extremely limited use of reason and logic-- their ability is barely greater than that of a wild animal.
- Inability to communicate in any (human) language.
Hosts of the Nerotonin 4 virus seem to have some kind of "hive mind" mentality. This means that the individual being is still capable of limited logical reasoning and thought, but generally discards its own well-being in favor of the horde or other infected if necessary. This includes situations in which groups of infected ignore self-preservation instincts, hunger, and any kind of danger they may encounter (these infected commonly being called "Cannon Fodder"), so that their prey (typically human survivors) gets distracted, injured or otherwise becomes an easier target for other parts of the infected horde.
Beyond the basic infected, new special strains of the N4 virus have allowed the infected host to operate independently of the "hive mind" mentality of normal infected. They instead rely on offensive or defensive abilities to tear through survivors. These mutations have effectively made these unique strains of infected a new "species". These mutants are commonly known as "Boss Zombies", and they appear to have the ability to summon their smaller brethren (both normal and mutant infected) into a swarm at will. They additionally seem to have a very limited ability to command their swarms where to go (typically, wherever a survivor is currently standing).
This ability seemingly only applies to infected animals and humans, which are typically hostile to anyone not infected by the same virus strain and invading their territory can be extremely dangerous, if the intruders are not prepared for an extremely high enemy to ally ratio.