Bee diseases, while not common have a severe effect on the future of beekeeping in the UK. Some of these diseases are so damaging, not just to bees, but to their capacity as food crop pollinators, that legislation exists to protect against the spread of these diseases.

American Foul Brood is a notifiable disease. Anyone finding evidence of this condition is required to notify the national bee unit. It is caused by injestion by larvae of bacterial spores, which grown inside the larva and ultimately kill them, leaving them dark and rotting inside the cells. See AFB on wikipedia

American foul brood:

An inspection by the MAFF Bee Inspector will be arranged, and if Foul brood is confirmed the bees will be destroyed. (Included in membership of the NBBKA is a bee insurance scheme, which pays for the cost of replacing contaminated equipment and bees in the event that this disease is encountered.)

Varroa mite - these are a little parasitic arachnid that affect bees. The chemicals that had kept these under control for the last few years are now resisted! It is essential that all beekeepers in the UK now learn about this pest, and take action to minimise it. One of the easiest and effective steps to counter this menace is to use mesh floored hives, and also to allow a small amount of drone brood, which is then culled before it reaches maturity. Drone brood pheronomes attract the mites away from the other brood - the drone brood acts as a bait. See varroa on Wikipedia

Varroa on a bee:

Varroa close up: