European foulbrood (EFB) is a bacterial brood disease caused by the Gram positive bacterium Melissococcus plutonius. EFB is listed in the OIE Terrestrial Animal Health Code (2011), but, unlike American foulbrood; it is not notifiable in all countries. The disease occurs in honey bees throughout the world, and may cause serious losses of brood and colony collapse. In many areas, the disease is endemic with occasional seasonal outbreaks, but, in a few countries, the scenario is different. In Switzerland, the incidence of EFB has increased dramatically since the late 1990s; it has become the most widespread bacterial brood disease in the UK, and Norway reported a regional outbreak of EFB during 2010 after a 30 year period of absence.
Geographically, the disease appears to vary in severity from being relatively benign in some areas but increasingly severe in others (Wilkins et al., 2007; Dahle et al., 2011; Grangier, 2011; Arai et al., 2012). Virulence tests on individual larvae using exposure bioassays (see section 9), shows that M. plutonius strains collected in different geographic European locations vary in their ability to cause larval mortality (Charrière et al., 2011).