10 days is actually a very reasonable amount of time for a virus to knock them out. Why did you lose the rasboras and not the rest of the tank? Same reason why when you get the flu your dog is fine and your pig is sick. Different viruses effect species.
Check with your LFS, if they had any strange die-offs recently you might find your cause of death. The best store in my city doesn't act like they don't get sick fish from their suppliers. They just turn the lights off on the affected tank and write "Not for Sale" on the tank until they have it cleared up. I've never lost a fish since I moved here and found them.