A good article on PBFD. Please read and keep this in mind. This is one of the reasons that Rich & Karen are so strict on making sure all boarders and turned-in parrots are current on disease testing.
This is also why you should not take your bird around other birds who haven't been tested and why you should ask about disease testing before boarding your birds or having someone with birds of their own pet-sit for you.
The lives our our feathered friends are precious... don't take the risk!