A few comments. First, no need to remember Sanchez' talk
from ASV, the gist of it is covered in a commentary
in the online journal Emerging Infectious Diseases,
which you can get from the CDC or Bocklabs servers
Second, the notion that a virus' genetic stability
in nature is a close and direct concomitant of the
fidelity of its polymerase is very simplistic. Although
the stability of Ebola across geographic space
(1000 km) is truly remarkable, its stability across
time (20 yr) is much less so. That is because RNA
viruses are transmitted among their hosts as
quasispecies, not as single clones. If an inoculum
commonly consists of hundred, even millions of
infectious particles, there are few bottlenecks,
and the virus has no "reason" (please excuse
anthropomorphism) to discard the successful,
predominant members of the quasispecies for some
polymerase-induced variant. As a result, many RNA
viruses are stable in sequence for many years,
despite error-prone transcriptional machinery.
What about the stability across geographic space?
Again, we know nothing about the host for Ebola.
Perhaps it is a migratory species (birds, insects,
even some mammals are migratory). If so, the
distance from northern to southern Zaire might
not seem so imposing.