Chalk Brood has persisted in both Hive 1 (WBC) and 1b (14 X 12), both hives originating from Hive 1  (14 X 12).  Incidence has reduced in Hive 1 since removal to WBC.

Chalk Brood is caused by the fungal organism Ascosphaera apis.

Three stages in appearance – Initially  white & fluffy;   Secondly swollen, filling the cells, the larval mouthparts may appear as a yellow protrusion; Finally, the stage most easily identified, they mummify, shrinking & hardening, changing colour to grey and black.  It is  at the final stage, when the fungus is sporulating and at its most contagious,  that the bees can easily remove the mummies from the cells and drop them on the floor of the hive

Chalk brood is a fungus and by nature likes damp conditions.  Keep the hives dry by raising them off the ground and  using  Open Mesh Floors.
It is known that high levels of carbon dioxide in a colony aggravates chalk brood.
Nutrition is important. Don’t let the colony run short of food at any time and make sure there is plenty of pollen.
Keep colonies strong in the ratio of bees to brood. Resist any manipulation that will result in a low number of adults, e.g. making up a nucleus and leaving it in the same apiary where some bees will fly home.  Resist transferring brood from hives with a chalk brood problem to other colonies.