Sac Brood is a viral disease. Adult nurse bees clean infected brood cells and, in turn, contract the virus.
Symptoms/Identification
Dead brood positioned upright in cells, their bodies a dark white, grey, or brownish-black color with the uppermost portion(head) darker than the rest of the body.
How it Spreads
Infected equipment
Moving infected combs to uninfected hives
Drifting/Robbing
Treatment
Requeening
Feeding pollen and syrup
Moving colonies to a sunny location
Prevention
To help prevent Sac Brood, always sterilize your equipment after working someone else's bees. Requeen every 1-2 years. Maintaining strong colonies and treating for pests namely, Varroa, will greatly reduce the stress on a colony and help it fight off disease.