Which disease (A3)?

View answer

Correct answer: 2 (European foulbrood)

European foulbrood is a contagious epizootic disease of honey bees. It is caused by the bacterium Melissococcus plutonius. Only the brood is affected by European foulbrood. Adult bees often act as carriers and vectors of the pathogen, but they themselves are generally not infected. It is not yet known with certainty whether M. plutonius is able to multiply in the gut of adult bees.

As long as the colony is able to remove all diseased larvae from the hive, no typical symptoms appear. Clinical signs become visible only when, due to the spread of the disease, insufficient brood care and reduced cleaning (diseased larvae remain in the combs), symptoms develop—generally only when the disease has already reached an advanced stage.

Field symptoms and diagnosis:

• weak colonies
• patchy brood pattern
• larvae become flaccid and turn yellowish to brownish
• diseased and dead larvae lie in all possible positions within the cells
• matchstick test: the mass is viscous and shows little or no ropiness (less than 1 cm)
• often a sour odor, sometimes fecal
• dark brown to black larval remains (scales) in the cell that can be easily detached from the surface
• occasionally capped brood is affected; in contrast to American foulbrood this is rather rare. In such cases the cappings are flattened or sunken, sometimes perforated or removed, dark in color and often moist
• some cells remain capped; bees do not emerge, particularly at the edge of the brood area

Such abnormal signs in the brood must be reported immediately to the apiary inspector. The inspector assesses the colonies and determines whether they are healthy, suspect, or diseased. In cases of suspected disease or diagnostic uncertainty, brood samples showing signs of disease are taken and sent to an analytical laboratory. If the clinical symptoms of European foulbrood are unequivocal, the inspector may dispense with sampling and laboratory diagnosis.

What can the beekeeper do?

It is recommended to strengthen bees’ natural defenses against disease by applying the principles of good beekeeping practice. Colonies are healthy when they develop well (adult bees and brood), display good hygienic behavior, and produce good yields. In practice, these are referred to as strong or vital colonies (see cover image). Colony vitality depends on many factors. Beekeepers mainly have the following levers of influence:

• Apiary locations with good nectar flows (continuous food supply) and a suitable local climate.
• Regular creation of young colonies and replacement of weak colonies.
• Selection of queens with sufficient vitality traits (colony development, hygienic behavior).
• Regular renewal of combs.
• Varroa mite control in accordance with regulations – hygiene in the apiary.
• Caution when taking over bees from other locations (diseases!).
• Avoid any importation of bees from regions outside Europe.

► PDF poster: Recognizing diseases

► Next question ►►