American Foul Brood (AFB), is caused by the spore-forming Bacillus larvae. It is very widespread and destructive as a bee brood disease. The larvae is a rod-shaped bacterium, and is visible only under a high-power microscope. Bee larvae up to 3 days old are infected by ingesting spores present in their food. Bee larvae less than 24 hours old are the most susceptible. Spores germinate in the gut of the larva and the bacteria begins to grow being nourished by the larva. Spores will not germinate in larvae over 3 days old. Infected larvae normally do not die until after their cell is sealed. As it grows, the vegetative form of the bacterium will die but not before it produces many millions of spores. And so, each now-dead larva may contain as many as 100 million spores. The disease only affects the bee larvae and it is highly infectious and deadly to bee brood.
The best field test is to touch a dead larva with a toothpick, twig or matchstick. It will be sticky and "ropey" as it is withdrawn from the cell. AFB has a very specific odor, and experienced beekeepers can sometimes detect the disease upon opening a hive. Indeed, at one time whilst I was working for a commercial beekeeper who had a major AFB problem, I was able to enter a yard and accurately mark all the affected hives just by standing in front of the entrance and picking up the odor. On an infected frame, capped sunken cells are present. Some of the cells are usually only partially capped. So, combined with the smell, sunken cells, shrivelled dark-colored larva and matchstick "test", it is usually a fairly easy diagnosis.
Spreading the Disease : As the bees work removing the dead larvae and cleaning the cells, they move and distribute the spores right through the hive. Stored honey is also contaminated with spores. Eventually the hive weakens from the infection and loss of brood. Robbing will then easily occur and the diseased honey will spread through other hives and apiaries. Additionally, as the beekeeper works the hives, infected bee equipment will be removed and mixed and exchanged into other hives, infecting and spreading the disease.
The AFB spores are extremely long-lived and resilient and can remain viable for 40 plus years in honey and beekeeping equipment. Thus honey from an unknown source should never be fed to bees, and used beekeeping equipment should be considered a risk.
Treating AFB : Spores are generally present in every hive. Once diseased larvae die within the hive, millions of spores are released. Antibiotics and drug treatment may be used accordingly to the particular country's laws. However resistance is a problem, and some countries which have adopted the rather radical method of requiring all AFB affected hives to be completely burned have successfully kept the disease under control. Other countries have the less radical approach of allowing the equipment to be treated by dipping into particular solutions and/or flame scorching. Other laws also allow the bees from the affected hive to have been earlier shaken onto treated equipment.
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