Which disease (C5) ?

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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 are often carriers of the pathogen and act as vectors of the disease, but they generally do not become infected themselves. Indeed, it is not yet known with certainty whether M. plutonius is able to multiply in the intestine of adult bees.

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

Symptoms and field diagnosis:

• weak colonies
• patchy brood pattern
• larvae become flaccid and turn yellowish or brownish
• diseased and dead larvae lie in various positions within the cells
• matchstick test: the mass is viscous and little or not at all stringy (less than 1 cm)
• odour often sour, sometimes reminiscent of faeces
• dark brown to black larval residues (scales) in the cell that can be easily detached from the surface
• occasionally capped brood may be affected, but in contrast to American foulbrood this is rather rare. In such cases, the cappings are flattened or sunken, sometimes perforated or removed, dark in colour 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 the bees’ natural defences against diseases by applying the principles of good beekeeping practice. Colonies are healthy when they develop well (adult bees and brood), show good hygienic behaviour and achieve 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:

• Location with good nectar flow conditions (continuous food supply) and a suitable local climate.
• Regular formation of young colonies and replacement of weak colonies.
• Selection of queens with sufficient vitality traits (colony development, hygienic behaviour).
• Regular renewal of frames.
• Varroa mite control in accordance with regulations – hygiene in the apiary.
• Caution when introducing bees from other locations (diseases!).
• Avoid any importation of bees from regions outside Europe.

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