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Several possible causes for the occurrence of such a viral strain have been suggested throughout the media. Romero’s work suggests that exposure to high-level radiation omitted from a satellite explosion, re-entering earth’s atmosphere, could be responsible for such an extreme cellular mutation, capable of regenerating cells within recently deceased bodies. In the ‘Resident Evil’ series, the outbreak results from exposure to the fictional T-Virus, developed by the infamous Umbrella Corporation in an attempt to create the ultimate bio-weapon. Other sources deem the cause to be exposure to human rabies-like strains which could account for the violent, psychotic behaviour exhibited by said creatures (i.e. unprovoked murderous conduct). It is also thought by some that it is a representation of the coming apocalypse – a plague of the undead sent as a punishment for the sins of mankind.

We will look at the cause in terms of infection with a mysterious virus (of unknown origin). This virus is likely to be a particularly lethal and powerful strain – as it is capable of inducing death and reanimation in its host, and would be unlike any virus seen before. Generally speaking, viruses act by invading the cells of the host organism and taking over cell metabolism and machinery in order to generate viral proteins etc. These newly generated viruses are released (via bursting of the host cell membrane) and then go on to infect neighbouring cells.

Several theories have been suggested concerning how such a virus would be capable of regeneration of dead cells. Studies have suggested that immediately after death there is still a certain amount of activity in the brain for a short period. When infected with this virus (possibly due to radiation exposure etc.), the virus is somehow able to harness this electrical activity and cause regeneration of dead tissue – resulting in the person being in a ‘zombified’ state with limited functions and basic primal urges – the need to feed on warm flesh for example. The host no longer has control over their actions and will strive to satisfy this hunger against all odds.

Also, there is the possibility of inter-individual variation in response to exposure to this illusive virus. People may be affected differently by the virus (this concept has been recognised with several currently treated viruses) – we all differ in terms of our immunological response to invading pathogens. For example, the presence of resistance genes may mean that certain individuals display immunity to this ‘zombifying’ virus (even when bitten by an infected individual). Conversely, others may be more susceptible to infection (e.g. due to mutations, compromised immune system etc.). Intense study and research would be necessary in order to determine the exact mechanisms of the virus in question – understanding how it is spread for example would determine the appropriate quarantine procedures. To eradicate this viral threat, a successful antivirus or vaccine would have to be developed.

For more information on the zombification process (stages/warning signs etc.), see the infection section.