Copyright © 1996, 1998 by Kevin Clark ( kevinc AT cnetech DOT com). All Rights Reserved.
Disclaimer
http://www.geocities.com/pentapod2300/best/kaferrot.htm
I was looking back through Kafer Dawn to refresh my memory for my new campaign there, and just happened to re-read the section on Kafer Rot, when I noticed something.
Kafer Rot is attacking terran crops in the areas where Kafers are present. I rechecked the city/town damage lists and they don't mention any type of Kafer biowarfare weapon being used. The Kafer Sourcebook mentions that Kafers are scavengers. They prefer rotting carcasses; their sausages are rotten meat/vegetable mixes. Humans can live for a while on Kafer food ( just lacking a few amino acids), so I would assume the converse is also true.
Given the near compatability of food, I would say Kafer Rot is just an organism from a Kafer world. It is an accidental contamination ( like the original unplanned introduction of Old World diseases to the New World on Earth). Removed from its native environment, there are no organisms checking its growth.
It arrived as 'mold' spores in the Kafer's food, or maybe even 'carried' inside or outside of the Kafers themselves ( ie athletes foot). A healthy Kafer's high levels of gut/skin bacteria and immune system would protect them from it. The spores are either released off the skin, or when Kafer dung dries up and the spore laden 'dust' is carried off by the wind.
Kafers do not have much knowledge of biology. If the human prisoners on Station Arcturus came down with Kafer Rot, and it was noticed, they would have dusted/bombarded more of the planet with the 'spores' ( they may figure this out and use it in the future). They didn't, so I believe an accidental contamination is the most likely cause.
This gives Earth hope that human bioweapons will still take the Kafers by surprise.