American foul brood
American foul brood (AFB) is a virulent disease of honey bee larvae that can be found in all continents and most countries where it has been looked for and where statistics are available. The name bears no relation to the geographical distribution of the disease - simply referring to the place where it was first described.
Beekeepers should know what healthy worker brood looks like, so that they can recognise any abnormalities immediately. Healthy worker brood cappings vary in colour from very light to dark brown. They look dry, with a good even brood pattern and few empty cells. The top of the cell is slightly convex. Drone brood can be recognised by its larger cells and domed cappings. Even where the brood pattern is more haphazard, for instance where the queen is old or starting to fail, the cell cappings should still look normal.
American foul brood diease is found within sealed brood cells. This is where the larvae are completing their development into adult bees. American foul brood is caused by a spore forming bacterium called Paenibacillus larvae. The honey bee larvae are infected by the bacterial spores contaminating their food. The spores germinate in the larval gut and then move in to infect the tissues breaking them down completely. Infected larvae normally die, their tissues becoming a glutinous mass of infective bacterial spores. The disease usually progresses gradually until it has killed most of the brood. The colony then cannot replace the old bees as they die and the colony dwindles down until it finally dies out.
When an infected larva dies in a sealed cell it changes the appearance of the cell cappings. The cappings become dark, moist-looking, sunken and perforated with a jagged hole made by the adult bees trying to remove the sticky body of the infected larva. At this stage the remains of the larvae have a slimy consistency and if a small stick or matchstick is inserted and withdrawn slowly then these remains can be pulled out in a brown, mucus-like thread or 'rope'. This is a reliable field test for the presence of AFB.
The dead larval remains dry out to form a hard 'scale' that sticks tightly to the base of the cell and cannot be removed. As a result, brood combs become severely contaminated with bacterial spores. This allows the disease to spread from colony to colony even after the colony has died. The spores are very resistant to extremes of heat and cold and are capable of remaining infective for more than 50 years. Bee management techniques that move combs between colonies have the potential to spread disease quickly.
Using antibiotics to control AFB is not effective, only serving to suppress the signs of disease but allowing the disease to spread widely and risking antibiotic contamination of the honey. The 'shaking method' (see external link to is moderately effective. However, for satisfactory disease control the most effective control method is to kill the infected colony and burn the combs safely in a deep pit so the ashes can be buried after the fire goes out. The hive should be scorched with fire to sterilise it and other equipment washed thoroughly in hot soapy water.
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- Language English
- Author Bees for Development
- Publisher Bees for Development
- Published Date October 2016
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