Here is a picture taken in the Dry Tortugas of white band disease.
Below is a picture also taken in the Tortugas of black band disease.
This disease actually kills the coral as the band crosses the coral leaving behind just a skeleton. A marine biologist studying these diseases told me it was possible to remove the disease by simple fanning it away from the coral... but there's a catch. The tissue that has been fanned away also needs to be collected since it is very contagious to the coral including all the surrounding corals.