Spores would be worse (e.g. can survive dry like anthrax). But viruses are small and can get around if they stay at the right moisture and pH.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2672.2010.04778.x/full#f1
Ebola can survive far longer than the CDC is saying
Has it ever broken out in a less humid climate? West Africa is wet. The virus stores well for research dried. Well, freeze-dried.