European foulbrood is a disease of bee brood caused by the bacterium Melissococcus plutonius. Other bacteria may also be involved. The young larva is infected via the food, the bacterium then multiplies in the midgut and the larva often dies before or even after capping. The disease can take a mild but also a severe course, leading to the death of the colony.

European foulbrood has been detected and is widespread on all continents where the western honey bee occurs.

Diseased larvae contain large amounts of bacteria due to the mass reproduction of the pathogen in the midgut. The faeces that the larvae release before pupation are heavily contaminated. During cell cleaning, the cleaning bees and subsequently the surfaces in the colony, the stored food and the other bees are contaminated.

Transmission in the colony: The pathogen is spread in the hive by cleaning and nurse bees and passed on to the larvae via the food.

Transmission from colony to colony: The pathogen is transmitted by the bees through flight and robbing. However, transmission through beekeeping activities, such as swapping honeycombs or combining healthy and sick colonies, is also particularly important.

Typically, the dead round maggots are initially yellowish, later brownish in colour and often lie twisted sideways in the cells. If a large number of larvae die before capping in the round maggot stage, this can lead to a brood nest with only a few capped brood cells. If the larva dies after capping, sunken, partially cracked cell caps are a sign of the disease. The cell contents are usually not or only slightly stringy and dry over time to form a dark, shiny scab that easily detaches from the cell wall. The removal of dead open brood leads to a patchy brood nest. If the queen re-pollinates here, brood areas with different larval ages are created, resulting in a very uneven brood pattern.

As a rule, the sweeping swarm method, including melting down the combs and cleaning and disinfecting the hives, is the method of choice. Hoping for spontaneous self-healing or simply removing and destroying individual brood combs with diseased brood is not a sufficient and recommendable measure from today's perspective. There are no authorised medications available in Austria for drug therapy.

Consistent comb renewal is recommended as a preventative measure. Ideally, separate tools should be used for each apiary to prevent the spread of pathogens. In general, only healthy, strong colonies should be kept, as these have better defences. Caution is advised when purchasing colonies and equipment.

European foulbrood occurs sporadically in Austria's honey bee colonies. The disease is not notifiable in Austria, so there is no exact data on the frequency of outbreaks.

European foulbrood is a disease of bee brood caused by the bacterium Melissococcus plutonius. Other bacteria may also be involved. The young larva is infected via the food; it usually dies before but also after capping. Dead larvae turn yellowish, brownish to black in colour and the larva turns into a mushy, sometimes watery granular mass (in exceptional cases thread-like), which then dries into a dark, shiny, loose-fitting scab. In rare cases the individual survives. If the larva survives, the hatching bee is usually dwarfed. In some countries, e.g. Switzerland and Great Britain, European foulbrood is of greater significance. In Austria, it currently occurs sporadically.

The larvae are infected via food. Young larvae up to two days old are most susceptible to infection, but older larvae can also be infected. The pathogen multiplies en masse in the midgut of the larva. The larvae usually die at the age of four to five days, i.e. before mating.

Symptoms

If the larva dies before mating, the larva lies limp, often twisted sideways in the cell. The body segmentation is barely visible and a dirty yellowish lump may shine through at the rear, blind end of the intestine. If a large number of larvae die before capping in the round maggot stage, this can lead to a brood nest with only a few capped brood cells. The cleaning behaviour of the cleaning bees results in a patchy brood nest.
If the brood dies after capping, the cell caps are often full of holes and sunken in or may be completely missing. The cell contents can either be a mushy, brown mass (usually not stringy in a match test) or a dried scab with a dark, shiny surface. This lies loosely on the cell floor and can be easily lifted out of the cell as a scale with tweezers.
Other bacteria, such as Streptococcus faecalis, Paenibacillus alvei and Achromobacter eurydice, are also involved in the symptom picture to an extent that varies from case to case. This can result in a different appearance or a different odour development in the dead brood.

Course of the disease

The course of the disease can range from mild to severe. If the disease is mild, a colony can recover spontaneously. If the disease is severe, it can be protracted and spread like an epidemic. Various factors influence the course of the disease, such as the pathogen pressure and the genotype of M. plutonius, but also the genetics of the bee colony (susceptibility to disease, hygiene behaviour), environmental influences and lack of food.

Possible confusion with other brood diseases or disorders:

• American foulbrood: The dead larva sinks into a shapeless mass, a stick immersed in it forms a thread when pulled out ("thread-pulling in the match test"); this mass dries into a firm scab
• Sack brood: The dead stretch maggot turns into a liquid-filled sack, which later dries into a boat-shaped scab
• Varroosis secondary infections: The brood damage can look similar to European foulbrood, but is caused by viral infections, e.g. the acute bee paralysis virus. A high varroa infestation of brood can be observed
• brood that has died due to cold (e.g. during cold snaps in spring): Due to a disproportion between the colony strength and the brood area, the brood overcools and dies. Dead brood of all stages can be found, which may show discolouration (yellowish or grey) and signs of decay (shapeless decomposed mass)

Therapy

There are no authorised medications available for treatment in Austria. As a rule, the sweeping swarm method, including the melting down of the combs and the cleaning and disinfection of the hives, is the method of choice. Hoping for spontaneous self-healing or simply removing and destroying individual brood combs with diseased brood is not a sufficient and recommendable measure from today's perspective.

• Sweep off the colony, place artificial swarm on centre walls
• Sufficient liquid feeding (also stimulates the cleaning instinct)
• Melt down the combs
• Scrape off wax and propolis residues from the inside of the hive or clean with a steam jet
• Wash the equipment (hive chisels, feeding utensils) and hives with 3% hot caustic soda; rinse with clear water (ATTENTION - caustic soda is corrosive; protective clothing (goggles, gloves) is therefore essential)
• Or flame the hives with a gas burner
• Clean the honeycomb cabinet and beehive and flame them if necessary; clean non-flammable parts with caustic solution