Can a fish carry Velvet and not be infected?

[Skye008]

Can marine fish carry velvet (amyloodinium) or brook but not be infected by it? Here's my problem...

 

My nano tank has been set-up for approximately 4 months (16 AGA bow, 20 lbs of live sand, 17 lbs of LR, 96watt 50/50 powercompact light, Aquaclear 300 with carbon, Powersweep 214, 100 watt heater). Within a period of several weeks after the tank cycled, I added a firefish, some zooanthids, a gorgonian, some yellow pollyps, and some mushrooms. One month ago, I bought a tank-raised percula and one week later added another one from the same LFS. This is when the problems started.

 

The second clown immediately started showing discoloration, lack of appetite, small white bumps (smaller than ich), a slimy sheen on its body, and lethargic behavior. It died within three days of being introduced, and the other clown died shortly thereafter. I then added a wild-caught percula (it had been at the LFS for at least a month before I got it) that developed the same symptoms and died right after being treated with a formalin bath. The latest clown, a maroon, died within five days of being introduced. After doing the research, I suspect it's either an an outbreak of brooklynella or more likely amyloodinium in my tank.

 

However, the strange part is that the firefish has remained alive and well throughout this ordeal, showing no signs of either disease. All the corals are alive and doing well. Water quality appears to be pretty good (pH: 8.3, Ammo: 0, Nitrite: 0, Nitrate: less than 5, Ca: 400, temp: 78 or 79 F, SG: 1.024). If amyloo indeed killed my clowns, why didn't it infect the firefish? Is there such a thing as an uninfected "carrier"? More importantly, can I leave the firefish in the tank and still break the pathogen cycle by not introducing any more fish for at least 6 weeks?

 

Any help is appreciated.