Can a disease be airborne but not be contagious by other means?
Building on Josh King's answer to this question concerning the feasibility of a disease which dies with its host, can a disease be contagious by airborne means while not being contagious by fluid exchange or touch?
I'm trying to define an apocalypse virus story, but I keep running into scenarios where the zombie/berserker still constitute an unescapable threat even after they've all been cut down by automatic gun fire. Their fluids carry the virus into local water table, their flesh gets eaten by carrion birds. Even if none of that happens, the defeated zombie/berserker corpses will soon develop a variety of dangerous secondary infections unless the surviving uninfected can dispose of those corpses safely.
I'm discovering why most zombie stories don't have happy endings. The aftermath of any zombie outbreak is a continually repeating series of future disease outbreaks.
So to combat that, I am trying to limit the contagious stage of the disease to its victim's living and/or breathing moments. I'm trying to come up with a rational explanation for the death of a disease's host, also marking the end of the disease's threat to its survivors.
So can a disease be only contagious by sharing breaths?
This post was sourced from https://worldbuilding.stackexchange.com/q/46867. It is licensed under CC BY-SA 3.0.
1 answer
Let's imagine that the organism causing the disease (a virus) has two states, depending on whether or not it's inside its host.
State #1: Active
In this state, the organism is inside the host. It's feeding on nutrients it finds and subsequently reproduces, sending its offspring or replicas throughout the host's body. When it's in this state, it needs nutrients X, Y, and Z to stay actively reproducing; these nutrients can only be found inside the host's living body.
State #2: Dormant
In this state, the organism is outside the host. It can no longer access nutrients X, Y, and Z, and so it can no longer reproduce (this goes along with the definition of a virus). Therefore, it goes into a state similar to hibernation - a low power mode, if you will. For this, it needs nutrient A, which is only found in the ambient atmosphere. If nutrient A is detected and nutrients X, Y, and Z are no longer detected, the organism goes into State #2.
Reason for a lack of contagion after the host's death
Nutrients X, Y, and Z are only found in a living host's body while the host is in the grips of the disease, and Nutrient A is only found in the air. When the host dies, the system breaks down and Nutrients X, Y, and Z are no longer available in the correct form. The organism carrying the disease has no way to store energy, and so it immediately dies.
Additionally, the organism must resist all attempts to exit the host's body, except when it is forcibly exhaled. It will do what it can to remain in the host's internal organs, so it will try to avoid the respiratory system, skin, and areas with fluid where it might be released against its will. However, when it leaves the body encased in fluid, it dies, because none of the four nutrients are available. It also cannot spread via touch; the organism will do whatever it can to avoid the surface of a host so it can remain inside.
These can be explained by simply having the organism be in a much better position to survive if it stays inside the host. For instance, it could only be able to spend a very, very, very short time in State #2 before dying.
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