American Foulbrood – time to inspect

AFB is a bacterial disease of developing honey bee brood.  AFB spores infect the larva in the earliest larval stage (newborn to 2 days old), generally through nurse bees supplying infected food. Infection spreads quickly among the larvae, as nurse bees, which carry the bacteria but are not affected by it, move from cell to cell feeding larvae. Only a few spores (<10) may be infectious. Once ingested by the larva, the bacteria in the active vegetative form grows and reproduces within larval intestines to massively colonize the larval midgut.

As the bacteria numbers increase, they escape the larval gut and the infection spreads to all tissues of the developing larva, causing sepsis and cell death. Larvae do not die until just as the larvae are capped – at this stage infected larvae completely breakdown into a glue-like consistency, extremely difficult for house cleaning bees to remove. When conditions become unfavorable for the vegetative form, this bacteria forms spores. Spores can survive decades. A single dead, desiccated larva (called scale) may contain millions of potentially infectious spores.


To monitor for AFB in your colony look for sunken, greasy looking cappings with tiny perforations, Remove such cappings and look inside. If you see a brownish (café-au-lait to carmel colored) decaying larval body that you can’t lift out from the cell it likely is AFB. You need to quickly get a confirmation of the field symptoms and then, without delay, determine what you need do to help prevent further spread.  Confirmation includes ropy test, pupal tongue, Vita AFB test kit or Holst Milk test. Or get someone who can help confirm.


In the 1920s American Foulbrood (AFB) was a huge problem killing hives and causing the loss of thousands of dollars for U.S. beekeepers. Strict state bee laws were subsequently passed and state inspection and registration programs established. Individuals could call the Department of Agriculture and an inspector would arrange for an inspection visit. After years of enforcement, management and education (and widespread antibiotic use), AFB cases dropped dramatically. Subsequently  state apiary inspection programs were discontinued and inspections terminated. There is no current Oregon inspection service and the state law is no longer in force. Most unfortunately AFB has been detected in nucs sold the Portland area. Discovering and controlling American Foulbrood disease, like other bee diseases, is the responsibility of the beekeeper.


In the absence of AFB inspection in Oregon, Portland area beekeepers have set up volunteer task forces to help with confirmations.  Most beekeepers  are not familiar with AFB and lacking live meetings to bring frames for examination (nor are labs open to diagnose comb samples), the volunteers are willing to help  with diagnosis and confirmation. Task force members, with an invitation, are visiting apiaries of individuals who suspect, from field symptoms, they have a disease problem. There is no fee and no individuals will be identified. With persistent EFB this spring, and PMS likely to appear as the nectar flow dries up, confirmation of probable cause is important because beekeeper solutions are varied and different in AFB, EFB and PMS situations. Colonies with both AFB and heavy PMS infestations are best euthanized to avoid potential spread to neighboring colonies  – something that can be difficult to do, especially for beginners.

Active (undiagnosed) AFB infections often occur among the strongest colonies in an apiary (because they rob a weaker colony with AFB) similar to the spread of mites from weaker (mite bomb) to stronger colonies. Beekeepers should also be concerned that purchased nucs or weaker colonies that have failed to develop normally might be continuing to suffer from lingering (spring) EFB infections or from heavy mite populations that are killing colony adults and/or seriously interfering with brood development (recognized initially as spotty brood pattern). As supers are removed and you begin fall managements plan to look at capped brood especially if pattern is spotty for AFB or your colony has unusual smell. Now is the time to perform mite counts on colonies. Insuring colonies are free of AFB and mite bombs do not develop is basic to good neighbor beekeeping.