How do I justify viral zombies not dying out?

Question

Viral zombies, that is zombies that are alive, are much more terrifying than their undead equivalents. While they lack the required headshot of their undead brethren, they are faster and often smarter.

One disadvantage they do have is that logistically speaking, they will die out before they can become a full blown apocalypse (Like in 28 Days Later). But can this be avoided?

While it is never explained how, the infected in The Last of Us are able to survive years without food as well as exposure and below zero temperatures; a survival feature nearly exclusive to undead zombies.

How can I justify living zombies that can survive the elements?

Answer 1

Maybe the virus allows the zombies to go dormant when there is no animal life nearby. It lowers the infected host's metabolism to something akin to hibernation or along similar lines to insects that can survive winter freezes. Then there's the possibility that doing so allows it to stay alive for extended periods, only raising its metabolism in response to nearby life (sound, smell, whatever). At that point, the virus revives the host. This also explains why the host is so slow when it first senses life, but then speeds up as stiff, dormant tissues come to life.

This isn't going to give you immortal zombies. But you could stretch this to allow at least a few years. Longer, if wildlife rebounds after human civilization collapses.Since that would provide lower life forms the zombie can catch and eat for a bit of sustenance from time to time.

Answer 2

There seems to be a couple issues you've asked about: How can the virus spread into a full blown apocalypse, and how can virus zombies survive for long durations in the elements.

Spread

Spread is the easy problem to solve: give the zombie-ness as the last symptom of the disease....one that doesn't occur until after the person has been infectious for some time (days? weeks? months? you decide. Longer the period the more dangerous strangers are in your world). The virus itself is interested, biologically, in spreading as much as possible. It could have evolved as a "slow burner" that starts off as a relatively mundane infection, perhaps causing higher blood pressure or some other small symptoms.

As the disease progresses, it changes the bloodchemistry, causing heightened "fight or flight" responses to other living things. Simultaneously, absent of these stimuli, the bloodchemistry slows the metabolism. Add in some brain lesions in certain areas, and the person will see every living thing as "food" even if they retain some of their critical thinking skills (much like animals that are infected with parasites retain their abilities to move, but lose inhibitions that keep them from being eaten). Eventually this goes full blown zombie, viciously attacking any "meat" that comes near. The virus spreads from any fluids and tissue of the creature, and could even be airborne if you wanted. The complications of a water or airborne virus would be difficult to handle indeed.

Survival

If the body is kept more or less intact, and can be fed (by the zombie viciously attacking any "meat" that comes near), then it should be able to survive for some time. This can be enhanced by lowering the metabolism of the organism for some time, until spiking it with adrenaline in response to stimuli (there are instances of snakes spending many years sealed in wine bottles that wake up and attack the opener of the bottle. Obviously, we aren't reptiles, but bears hiberate, spending months not eating).

In terms of infection, the virus itself could provide safety there. Perhaps this virus enhances the immune system of the host to fight off infections, or attacks bacteria itself. You'd still get the "dirty zombie" look, you'd just not get the "rotten zombie" look. Add in biochemical changes that improve the body's response to trauma (enhanced swelling to reduce blood loss, or smarter clotting to seal wounds relatively quick, or both).

Exposure might cause some issues, but there's no reason the biochemistry changes that affect the fight or flight response and metabolism can't also introduce some form of resistance to frostbite or heat stroke. You're already going to be lowering body temp by "hiberating" when stimuli are absent.

Answer 3

This is really very simple. There exists an animal vector in which the zombie virus is not terribly damaging. The term for interspecies diseases is zoonotic. The classic example is the Ebola virus, which apparently has such a host, although as far as I know nobody's found it. Avian flu is another example, and likewise, swine flu. And, of course, the phenomenon can be beneficial, as in the case of cowpox, which confers immunity to smallpox in humans.

If, in addition, transfer from animal to human is unlikely (but not impossible), the virus can persist in the animal population, only occasionally crossing over to the human population and wreaking havoc.

Answer 4

How about a fungus-based zombie instead? The fungus spreads throughout the host, controlling brain-body function (see https://en.wikipedia.org/wiki/Ophiocordyceps_unilateralis for real-world examples of this -- the rest of the answer is pretty hand-wavy, I'm no mycologist). In the advanced stages, mushrooms blossom from the host (conveniently making them look proper rotted). Since most fungus feeds off of decay, you have a great source of resources; the fungus can feed off of rotting material in the hosts stomach (so no need to keep the digestive system running). The fungus drives the host to consume living creatures because they are a much more condensed source of energy. When such prey is not available, the host enters a dormant state. The fungus shuts down the body but keeps it alive by providing nutrients directly into the blood stream. To get those nutrients, it spreads from wherever it's host is rooted to the surrounding area (so a host beside a fallen tree might be preserved for quite awhile). You can imagine roots blossoming off of the host and leeching off of whatever else is around. Or maybe the fungus can cannibalize the host a little bit at a time, letting less critical pieces decompose in order to maintain the dormant state. When a threat or a new potential host is detected, the host body is reactivated, rising up from the muck to attack. Mycological colonies can be massive as well, so you could have lots of zombies all piling up against each other to preserve heat and share resources, maybe consuming the outer hosts first in order to better preserve more well-protected ones.

This also has the advantage that the fungus can survive independent of the host and in very inhospitable conditions, remaining dormant underground for years at a time. So even if the original outbreak is contained, there's no guarantee that humanity has been saved...

Answer 5

The military were working on genetically engineered super soldiers. Using the latest advances in gene therapy and insights gained from studying the DNA of animals with strong survival traits such as more efficient metabolisms, extreme temperature resistance, and ability to hibernate, a viral vector was being developed that altered the host's DNA to provide augmentations. The lab were working to resolve some issues including a high level of contagiousness, and a side effect that caused subjects to enter a violent rabid-like state. The virus escaped before their work was completed.

Because the zombies' DNA contains both the positive and negative genes from the experimental virus, they are able to survive longer than would be expected and in extreme conditions.