European foulbrood (EFB) is a disease that infects the brood of the honey bee, caused by the bacterium Melissococcus plutonius. This bacterium (formerly known as Streptococcus pluton) forms a capsule. This capsule is less resistant in comparison to the spore produced by Paenibacillus larvae, the pathogen of the American foulbrood.
The larvae become infected by ingesting contaminated brood food and up to the maximum age of 48 hours. The bacterium reproduces in the larvae’s midgut and the brood usually dies in the larvae phase. The larvae turn brown-black in colour and transform into a pulp, sometimes watery-grainy pulp (with threads in rare cases), which consequently dries, becoming smooth, shiny, loose scales.
Should the larva survive, the hatching bee will be lower in size and weight. The infection ranges from mild to severe. The course of infection is affected by food conditions.
European foulbrood is a serious problem in some countries, such as Switzerland and the United Kingdom. Infections are seldom in Austria, though.