I haven't seen a lot of references to Brackhaven's potential infection. Now, I haven't read Season 4, but I can't really see a good reason for tanking Seattle's economy except as a Sybil initiated thing.
Depends on what the Virus wants (and it DOES seem to want something...)
Look at the know infected:
Riser, an assassin, with links to the Smoker's club, a highly skilled wetwork team.
Fastjack, THE hacker of the known world.
Lanier: A VIP of one of the largest, most powerful MegaCorps on the planet.
Plan9: An individual with ties to the fringe (crazy) element of the world.... where, believe it of not, the first clues to the planetwide conspiracy would first be noticed.
Brackhaven: the governor of one of the most important sprawls on the North America and access to most of the world thanks to it's position as a trading port and the presence of every single Mega on the planet.
So, now you have,
The best info finder, Assassins, Corp assets, a city and rumor control all under the fingers on a Virus..... And it Seems to have intelligence and a plan....
*****
Best not sleep tonight, never know what is going to use your body while you're "away"