The causative agent of European Foul Brood (EFB) is the bacterium Melissococcus plutonius. The bacteria multiply in the mid-gut of infected larvae, competing with the larva for its food. Larvae that die from the disease do so due to starvation. This normally occurs shortly before their cells are due to be sealed.
Progression of the disease
The development of the disease within the colony is complex, and still not understood. It appears that infection can develop over a period of months or years, debilitating but not killing the colony. During this time, signs of the disease can become more or less severe, or disappear altogether. This may be due to how well the larvae are fed. When infected larvae are less well fed they are likely to suffer from starvation and die, but at times of plenty when infected larvae receive an abundance of brood food they will survive. However, when these larvae pupate they void their gut contents into the cell, contaminating the comb with infective bacteria. It is likely that the disease will eventually reach a level where most of the brood is infected, weakening and killing the colony.
Signs of European Foul Brood.
- EFB affects mainly unsealed brood, killing larvae before they are sealed in their cells.
- The EFB infected larva moves inside its cell instead of remaining in the normal coiled position characteristic of a healthy larva of the same age.
- When it dies it lies in an unnatural attitude – twisted spirally around the walls, across the mouth of the cells or stretched out lengthways from the mouth to the base.
- The dead larva often collapses as though it had been melted, turning yellowish-brown and eventually drying up to form a loosely attached brown scale unlike the hard black attached scales of AFB.
- When a high proportion of the larvae are being killed by EFB, the brood pattern will often appear patchy and erratic.
- A very unpleasant odour may sometimes accompany severe EFB infection, depending on the presence of certain other species of bacteria in the remains of dead larvae.
- A minority of infected larvae may die after the cell is sealed. In such cases, there may be sunken perforated cappings resembling AFB infection. However, the cell contents although brown and sticky cannot be drawn into a ‘rope’ as with AFB.
Diagnosis and Control of EFB
European Foul Brood is a Notifiable Disease under the Bee Diseases and Pests Control Order 2006. A Bee Inspector should be called upon to confirm any suspicions and a sample can be immediately diagnosed within the apiary using a field test kit. Samples of suspect comb may be submitted to the National Bee Unit at York. Here, fully trained staff carry out a rapid and effective diagnosis. Beekeepers can buy an EFB test kit with full instructions for around £10 per test, but EFB is notifiable and so the Bee Inspector must be called immediately if disease is suspected. The bee inspector will inspect and test your suspected colonies free of charge.
When a sample is diagnosed positive for EFB, weak or heavily infected colonies must be destroyed. Lightly infected colonies may be restored to health by shook swarm method, shaking them into a clean brood box installed with frames of new foundation. The bees will then start afresh with pristine combs. This method is called the “shook swarm” treatment. Treatment with antibiotic oxytetracycline administered by the Bee Inspector is permitted in limited circumstances, but a six month withdrawal period is laid down for any honey coming from that colony. The law does not permit the presence of detectable residues of antibiotics in food.
If you suspect you have found EFB, you MUST report it to the NBU via your Bee Inspector
Rules for Foul Brood Control
- Inspect your colonies every spring and autumn, specifically to check for brood disease. If you are unsure, seek advice from an experienced beekeeper in your locality. This is a good time to transfer brood frames from their over-wintered brood box into a newly scorched brood box. Scorch with a blow lamp.
- Do not transfer combs between colonies or divide colonies if you have any doubts about their health.
- Never bring colonies, comb or beekeeping equipment into the apiary unless you are sure that they come from a disease-free source. Always scorch second-hand hives with a blow-lamp before use.
- If a colony of bees dies out, seal the hive to prevent robbing, pending examination of the brood combs for signs of disease.
- If any colony appears not to be thriving, and the reason is not already known, examine the brood for signs of disease.
- Be suspicious of stray swarms. Inspect them for disease once they have become established.
- Regularly and systematically replace old brood combs in the apiary by melting them down and replacing them with foundation. It is a good idea to replace all frames in the brood box at least every 2 years.