European foulbrood is a disease of bee brood caused by the bacterium Melissococcus plutonius. Secondarily, other bacteria may be involved. The young larva is infected via the food; it dies either before or after mating. If the larva survives, the hatching bee is dwarfed.

European foulbrood is detected and widespread on all continents where the Western honey bee occurs.

Melissococcus plutonius forms capsules as a permanent form. These are comparatively less resistant than the spores of Paenibacillus larvae, the pathogen of American foulbrood. The capsules are found en masse in the feces of infested larvae and in dead larvae.

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

Transmission from colony to colony: Transmission occurs through the bees themselves during flight, predation or contact with bee excrement (e.g. at water troughs). However, transmission through beekeeping activities is also particularly important, such as the purchase of comb material and equipment with pathogen contamination, comb swapping or the uniting of healthy with sick colonies.

Brood dieback

Sometimes the colony can recover on its own, or recovery can be supported by removing affected brood combs. In most cases, however, the sweep swarm method is the method of choice for a control measure. There are no approved medications available for drug therapy in Austria.

In general, only healthy, strong colonies should be kept, as these have better defensive capabilities. Caution is advised when acquiring colonies and equipment, such as setting up a separate quarantine stand for captured foreign swarms as well as newly purchased colonies.

European foulbrood rarely occurs in Austria's honey bee colonies. The occurrence of European foulbrood is not notifiable. Therefore, the frequency of occurrence is only surveyed on a random basis in the course of research projects. In the course of the project "Zukunft Biene" (Future Bee ), about 200 apiaries were checked for clinical symptoms on three visit dates in the years 2015 to 2016; European foulbrood was not observed.

European foulbrood is a disease of bee brood caused by the bacterium Melissococcus plutonius. Secondarily, other bacteria may be involved. The young larva is infected via the food; it dies either before or after mating. There is a brownish-black discoloration and transformation of the larva into a pulpy, sometimes watery granular mass (filamentous in exceptional cases), which then dries into a smooth, shiny, loose-fitting scab. If the larva survives, the hatching bee is dwarfed. In some countries, such as Switzerland and Great Britain, European foulbrood is a major problem. In Austria, it occurs rather rarely at present.

Infection of the larva takes place via food and is possible up to an age of 48 hours. The pathogen multiplies in the midgut of the larva. Usually the larva dies after a few days while still in the round maggot stage.

Symptomatology

Often the larva dies in the round maggot stage, more rarely after mating. If the larva dies before mating, the larva lies limp, often twisted sideways in the cell. Body segmentation is barely visible and a dirty yellowish lump may show through at the posterior, blind end of the intestine. The cleaning behavior of the cleaning bees results in a patchy brood nest.

If the brood dies after capping, the cell covers are often pitted and sunken or may be completely missing. A black, varnish-like coating on the inside of the cell cap containing large amounts of bacteria is possible. The cell contents may be either a pulpy, brown mass (usually not stringy in match specimen) or a dried scab with a smooth, shiny surface. This lies loosely on the bottom of the cell and can be easily lifted out of the cell as a scale with tweezers.

If the larva survives, the hatching bee is dwarfed. Other bacteria are also involved in the symptom pattern to varying degrees from case to case, such as Streptococcus faecalis, Paenibacillus alvei, and Achromobacter eurydice. This may result in a different appearance or odor of the dead brood.

Course of the disease

The course of the disease can be mild to severe. The course of the infection is influenced by the conditions in which the brood occurs.

Possible confusion with other brood diseases or disorders:

• American foulbrood: the dead larva sinks to a formless mass, a rod immersed in it forms a thread when pulled out ("threading the matchstick test"); this mass dries into a sessile scab
• sac brood: the dead brood maggot turns into a fluid-filled sac, which later dries up into a boat-shaped scab
• Subsequent infections of varroosis: Brood damage may look similar to European foulbrood, but is caused by viral infections, such as Acute Bee Paralysis Virus. A high varroa infestation of brood is observed
• dead brood due to chilling (e.g. during cold spells in spring): due to a disproportion of the colony strength with the brood area, the brood cools down and dies. Dead brood of all stages can be found, which may show discoloration (yellowish or gray) and signs of decay (shapeless decomposed mass).

Therapy

There are no approved medications available for drug therapy in Austria. Sometimes the colony can recover by itself, or the recovery can be supported by removal of affected brood combs. In most cases, however, the sweeping swarm method is the method of choice for a control measure.

• Sweep the colony, place artificial swarm on center walls
• Sufficient liquid feeding (also stimulates the cleaning instinct)
• Melting of the combs
• Scrape wax and propolis residues from the inside of the hive or clean them with a steam jet.
• Washing of the equipment (stick chisel, feed dishes) and hives with 3% hot soda lye; rinse with clear water (ATTENTION - soda lye is corrosive; protective clothing (goggles, gloves) is therefore absolutely necessary)
• Or flaming of the hives with gas burner
• Clean honeycomb cabinet and beehive and possibly flame them; clean non-flammable parts with lye.

Prevention

In general, only healthy, strong colonies should be kept, as these have a better defensive power. Caution should be exercised when purchasing colonies and equipment, such as setting up a separate quarantine stand for captured foreign swarms as well as newly purchased colonies. To prevent the spread of European foulbrood on the farm, no forage or pollen combs should be hung on the farm if European foulbrood is suspected. In addition, honey should not be fed, only sugar or feed syrup. Bee drinkers should be protected from droppings. A good spring colony is favorable for the resistance or self-healing power of a colony.