European foulbrood (EFB) is a bacterial disease affecting honeybee larvae, caused by the Melisococcus plutonius bacteria. In spite of the name, it is not just found in Europe but is widespread--and can be found in North and South America, the Middle East and Asia.
Young honey bee larvae become infected with M. plutonius when they are fed contaminated food. The bacteria multiply rapidly in the mid-gut of the young larva, resulting in starvation just prior to capping. Some larvae may survive and enter the pre-pupal stage but die shortly thereafter.
Like American Foulbrood (AFB), EFB bacteria kill the larvae leaving empty cells left in the comb. However, EFB is much less serious than AFB. EFB shows up when the colonies have been under stress due to other diseases, colonies nearby, poor management and weather. EFB affects bee brood similar to AFB except that the disease affects open brood, i.e. the larvae are affected before they are capped. Approximately 10% of the larvae die after capping and this often leads to misdiagnosis because of the similarity to symptoms of American Foulbrood.
At the start of the main nectar flow, EFB mostly disappears or becomes non-detectable. The infestation may reappear in the fall. Re-queening seems to help because certain bee lines appear less susceptible than others (due to cleaning behaviour), and the replacement of the queen involves a break in the brood cycle of the colony.
TransmissionEFB is spread by mechanical contamination of honeycombs, and tends therefore to persist from year to year. It can also be spread by bees that survived infection as larvae, and spread the bacteria in their feces.