Overview of European Foulbrood: A Bacterial Disease Affecting Honey Bee Brood

European foulbrood is a bacterial disease that effects honey bee larvae before the capped stage. European foulbrood disease is characterized by dead and dying larvae which can appear curled upwards, brown or yellow, melted, and/or dried out and rubbery. The causative bacteria, Melissococcus plutonius is ingested by honey bee larvae after which the bacterium competes for food inside the larvae. If the bacteria out-competes the larva, the larva will die before the cell is capped. Alternatively, the bee may survive until adulthood if the larvae has sufficient food resources. European foulbrood should not be confused with American foulbrood (AFB), which is caused by a different bacteria that produces different symptoms and control requirements. European foulbrood disease is considered to be more problematic in situations where forage nectar is sporadic, or other situations that result in fewer nurse bees in colonies to feed larvae. At the onset of nectar flow in early spring, forage recruitment of house bees may increase rapidly resulting in few bees in colonies to feed honey bee larvae. Often, when the nurse bee to larvae ratio stabilizes later in the season, or remains stable throughout a season, symptoms disappear. However, this disease can occur throughout a season and will sometimes not clear up on its own. In severe cases, colony death can occur. Also, yearly reoccurrence of EFB from contaminated combs and equipment can occur. The bacteria that causes EFB does not produce spores, but combs contaminated with the bacteria can still reinfect honey bees in subsequent years.