American Foulbrood

Historically, this is the most virulent disease of honey bees throughout the world. The bacterium res ponsible for the disease, Paenibacillus (= Bacillus) larvae, form heat- and droughtresistant spores that persist for years and germinate under favorable conditions. It is expressed in older larvae and young pupae, though infection occurs earlier, and young larvae are more susceptible than older larvae. Infected individuals turn darker in color, then black, and eventually collapse into a hardened mass in the cell. Signs of infection include a sour odor, perforated or sunken caps on the cells, and the presence of black deposits in the cells. If foulbrood is present, insertion of a twig or probe into a suspect cell will result in a gummy, stretchy substance being drawn out of the cell, often forming a thread or rope and called “ropy.” Field diagnosis is possible by experienced inspectors, but is best confirmed microscopically or by molecular techniques. There are several subspecies of P. larvae, and P. larvae ssp. larvae is considered responsible for American foulbrood, with other subspecies also affecting honey bees.

Transmission occurs by feeding infected honey or pollen, by using infected equipment, and sometimes by installing infected package bees or queens. Feeding bees sugar syrup therefore is preferable to feeding them honey, and disinfection of hive tools is always recommended. Natural transmission from hive to hive can occur through robbing behavior. Queens and workers can carry the disease. Bee colonies that are infected normally are eliminated by burning them. Antibiotics can be fed to colonies to prevent infection.