The bacterium M. pluton is a very robust organism. It can survive for months on contaminated equipment.
It usually enters the colony through infected bees, equipment or honey introduced by the beekeeper. The organism can be present in a dormant form for some months before signs are visible.
The infection can spread throughout the apiary during hive manipulation where infected combs are introduced to healthy colonies. Bees drifting from one hive to another and contamination of drinking water are other possible means of spread.
Nurse bees transmit the bacteria during cleaning and feeding, when the mouth parts become contaminated. The organism is then accidentally fed to healthy young larvae, where it finds its way into the mid-gut and multiplies.
European foulbrood disease primarily affects young larvae, killing as many as 90%. Adult bees also can be affected in severe outbreaks.
Because the disease can be present in colonies for months before signs become visible, most hives within the apiary show infection at the same time.
The disease is most likely to be seen in early spring at the first expansion of brood or at the start of a nectar flow. It may also appear at any time after bees have been stressed, such as after moving the apiary.