Not anything particular to danios that I am aware of, although they are subceptable to all other known fish diseases. Maintain a healty tank, and I swear those danios live for freaking ever. I've got two long finned blue ones that keep on trucking, and they are at least five years old now. The biggest thing with danios is that they have a tendacy to nip each other's fins, especially the long finned varieties, which gives them a particularly ratty look.
~~Colesea