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.
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.
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