Angolans die from Ebola-like bug Update: WHO: No end in sight Death Toll 210

Question for the experts!
I was listening to the Art Bell show the other night, and he did an interview with a Microbiologist who said the the current version of the Marburg virus has morphed and become more deadly than the original version. I believe the mortality figures in quoted for the Original Marburg virus was around 33-37%.

How has this virus morphed into one which kills close to 90% of those who get infected? It also appears to be airbourne.

Can someone with a scientific background answer this question?