The Department of Primary Industries and Regional Development (DPIRD) has implemented preventative measures including strong border controls to safeguard WA’s bee populations.
European foulbrood disease is caused by a bacterium Melissoccoccus pluton (formerly called Streptococcus pluton), which invades the mid-gut of four to five-day-old larvae and multiplies rapidly causing death.
Unlike American foulbrood, chalkbrood and sacbrood diseases which affect the larvae in sealed brood cells, European foulbrood disease commonly affects larvae in open brood.
European foulbrood disease primarily affects young larvae, adult bees also can be affected in severe outbreaks.
Bacteria multiplies in the mid-gut of infected larvae, competing with the larvae for food. This often results in the death of the larvae before capping.
Heavy infestations can kill as much as 90% of the brood, weakening the colony over time and leading to colony collapse.
Because the disease can be present in colonies for months before signs become visible, most hives within the apiary show infection at the same time.
Infected larvae move about inside the cell instead of staying in the normal curled position. Unlike American foulbrood disease, where the larvae consistently slump to the lower side of the cells, larvae infected with European foulbrood appear twisted in different positions.
Larvae in the initial stage of infection often turn with their backs facing towards the cell opening, so that the mid-gut is clearly visible.
Closer examination of the infected mid-gut may show that the gut is enlarged and white, instead of the yellow-brown seen in healthy larvae.
The bacteria may not cause any odour in infected colonies. However, secondary invasion by other bacteria could result in a sour or foul smell. The secondary bacteria that flourish in dying larvae can cause variations in the classic signs of European foulbrood disease.
Once the first signs appear, strong colonies can become non-productive within four weeks and the entire colony may die out if severely affected.
In severely affected colonies, the capped brood may appear irregular, similar to a failing queen or to American foulbrood disease. However, the brood cappings do not appear dark and sunken as with American foulbrood.
The disease is most likely to be seen in early spring at the first expansion of brood or at the start of a nectar flow. It may also appear at any time after bees have been stressed, such as after moving the apiary.
The bacterium M. pluton is a very robust organism. It can survive for months on contaminated equipment.
It usually enters the colony through infected bees, equipment or honey introduced by the beekeeper. The organism can be present in a dormant form for some months before signs are visible.
The infection can spread throughout the apiary during hive manipulation where infected combs are introduced to healthy colonies. Bees drifting from one hive to another and contamination of drinking water are other possible means of spread.
Nurse bees transmit the bacteria during cleaning and feeding, when the mouth parts become contaminated. The organism is then accidentally fed to healthy young larvae, where it finds its way into the mid-gut and multiplies.
Bacteria multiplies in the mid-gut of infected larvae, competing with the larvae for food. This often results in the death of the larvae before capping.
Infected larvae dissolve into a semi-liquid mass, sometimes described as molten. Their colour changes from a healthy pearly white to yellow then brown before drying out to loose brown scales.
Diagnosis can only be confirmed in the laboratory by smears taken from infected larvae or a honey test.
In selecting suitable larvae, it is important to select those that are at the initial stage of infection, before collapsing in the cell. Collapsed larvae may be invaded by secondary bacteria, which may prevent accurate diagnosis.
Should the disease become widespread, eradication may not be possible and it may be necessary to adopt control measures using antibiotics. Antibiotics, combined with good management, have been shown to control but not eradicate the disease. Written approval of an inspector is required before administering antibiotics to bees.
Hygiene is important in limiting or preventing the spread of the disease. Beekeepers should maintain good apiary hygiene, as follows:
- Avoid the introduction of bees and equipment from unknown sources.
- Avoid exposing honey combs or equipment to robbing. Store and fumigate spare equipment away from robber bees.
- Watch for signs of diseases.
- Report any brood abnormalities immediately to the Apiary Coordinator.
European foulbrood is a declared pest and beekeepers are legally required to report them.
Legal duty to report
Melissococcus plutonius corrig. is a declared pest in WA.
It is a prohibited organism under section 12 of the Biosecurity and Agriculture Management Act 2007.
This means that any person who finds or suspects the presence of European foulbrood must report it to DPIRD.
Reporting is not just a legal obligation; it's crucial for safeguarding your hives and nearby colonies. Early detection gives us the best chance to eradicate pests and diseases. By following best practices and reporting promptly, we can protect Western Australia’s healthy bee populations and stop the spread of harmful pests and diseases.
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DPIRD Apiary Team