Half moon disease is a disease that closely mimics EFB, but has only ever been identified in New Zealand. The larvae die and the appearance in the cell is pretty much identical to EFB. However there are no EFB bacteria, and in fact the disease is caused by a queen problem and is resolved if the queen is replaced.
The other thing that happens with half moon disease is the queen will lay multiple eggs in some of the cells.
I have just been at a bee disease seminar and a scientist was talking about this and their could be some interesting info for people in other countries. Here in NZ we do not have EFB, so cases of half moon disease can easily be identified. But his belief is that it is unlikely this condition only occurs in NZ and nowhere else. He thinks that because nearly all other countries have EFB, if half moon disease occurs it can be mis identified as EFB, and this is the reason why it used to be said that EFB could be cured by requeening.
He has studied real EFB and said it is very contagious, very virulent, and is not cured by changing the queen.
So after listening to all this, i thought maybe the reason people in the US are thinking EFB suddenly got a whole lot more virulent, might be that in the previous "mild" cases that would go away on their own or be cured by requeening, they were not even true EFB. And now, for whatever reason, real EFB has become more common.
I could be totally wrong, but it was interesting, thought i would share.