Illness on Pandora?

[Banefull]

Look at it from an evolutionary point of view.

Generally, an organism that lives inside the body of another organism does not want to kill its host. Pandora is a very stable environment where things have remained relatively unchanged for long periods of time. What generally happens over long periods of time is that "bugs" and their hosts tend to evolve in such a way that the host receives no ill effects from the bug. Now granted the "bug" still leeches nutrients but its no longer a disease in the sense that there are no longer any symptoms.

Humans have tended to be a migratory people. They arose in one region and migrated all around the world. Quite often disease came from "bugs" that lived in animals or were present in the environment in other. These bugs caused hardly any ill effects on their original host; however, it so happened by coincidence that they could also live in a human body with different results.

Cholera is perfect example of what I am talking about. Its a bacteria that lives perfectly fine by itself in an aquatic environment but it just so happens by coincidence that it can live in a human host with devastating results. The two species lived isolated from each other. History is full of recorded massive outbreaks of cholera; however, the more dangerous forms of the disease tended to be so deadly that it killed itself out once it could no longer get away with infecting new hosts. Think of the extremely deadly SARS virus that killed itself out very recently.

When you have a sparse population where transmission is limited to within a clan, anything too deadly and virulent will easily kill itself out. Likewise, having ill effects on a host could be devastating because if the host becomes weak as a result of illness, it could die from predators. The tendency would be to evolve towards masking itself with as few ill effects as possible.

Theres no doubt in my mind that there are "bugs" in the sense that they take nutrients from their hosts, its just that they have no noticeable effects on their host to be called a disease.