* Caused by: Bacillus larvae * Spore-forming bacterium * Highly contagious * Brood Disease American Foulbrood (AFB) is an infectious brood disease caused by the spore-forming bacterium Bacillus larvae. It is the most widespread and destructive of the brood diseases, afflicting queen, drone, and worker larvae alike. Adult bees, however, are not affected by AFB. Bacillus larvae occurs in two forms: vegetative (rod-shaped bacterial cells) and spores. Only the spore stage is infectious to honey bees. The spores germinate into the vegetative stage soon after they enter the larval gut and continue to multiply until larval death. American foulbrood spores are highly-resistant to desiccation, heat, and chemical disinfectants. These spores can remain virulent for more than forty years in combs and honey.