The Threat of American and European Foulbrood

In the world of beekeeping, there are few problems as catastrophic to bees as American Foulbrood (AFB). It is the most severe, problematic, and challenging of all the diseases that may affect a colony. It is also extremely contagious (to bees, not humans) and, if left to spread, can wipe out entire colonies. Plural!

Such is the impact that an outbreak of AFB should be reported to state authorities for a diagnosis. If confirmed, the most effective “solution” is to burn all hives and equipment. Why? Because the spores of AFB can remain active for up to 70 years!

Although having a similar name, European Foulbrood (EFB) is nowhere near as severe. This is because the bacteria from EFB don’t create persistent spores. Indeed, it’s possible for a colony to recover from EFB and it can be treated with antibiotics. But it is still a very serious disease that you really don’t want to see.

Note that these diseases are so widespread worldwide now that their names do not relate in any meaningful way to where you might find them. Both are evident in the US.

American Foulbrood


AFB is caused by the bacterium Paenibacillus and is a disease that affects honey bee larvae. It attacks young larvae, which are killed after they ingest infected food. The spores germinate within the larva and the bacteria grows. This germination happens only in larvae under 3 days old.

An infected larva will die after its cell is capped. The growth of the bacteria will also stop, but not before millions of spores are produced, with a single larva having as many as 100 million spores.

A one-day-old larva can be infected with as few as 35 spores but this number jumps quickly
A 2-day-old larva can be infected by a million spores, yet after 53 hours the larvae become immune.

A major problem with this highly contagious disease is that worker bees will incidentally promote its spread, merely by going about their business. For example, when a dead larva is found, housecleaning workers will clean up but, in doing so, spread active spores around the rest of the hive.

Even more damaging is that robber bees can enter a hive infected by AFB, unwittingly collect the spores, and return to their own colony – thus spreading the disease across colonies very quickly. If your bees are the bees doing the robbing…


Symptoms of AFB include:

  • Sticky or “ropey” larvae create threads when poked, that measure up to 2.5 cm
  • Larvae are dead and turn yellow to brown
  • Cappings may appear greasy
  • A distinctive sulfurous odor, although this is generally only noticeable when AFB is in the advanced stages

However, an accurate determination requires sending a sample to a laboratory.

IMPORTANT: Do not poke larvae you suspect as having AFB with your hive tool or anything else you will use around the hive. This is an assured way to spread spores throughout the hive and to other hives too. Use a toothpick.


Although AFB can be transferred between colonies very efficiently by robbers, beekeepers are unwittingly the major reason for its spreading. Hygiene-focused procedures can go a long way toward reducing the chances of spreading AFB.

  • Do not feed your bees from an unknown source. Commercial honey contains AFB spores over 90% of the time!
  • As a general rule, steer clear of used equipment. Aside from the initial purchase of hives and tools, beekeeping isn’t an overly expensive hobby. Rather than risk bringing AFB to your hives, consider new equipment rather than used.
  • Don’t transfer boxes between hives
  • Sterilize your hive tool occasionally
Some treatments exist that are considered to be helpful in preventing AFB
These include oxytetracycline hydrochloride and tylosin tartrate.

The use of chemical treatments is controversial since many believe strains of the bacterium quickly develop a resistance. In fact, as of January 1st, 2017, a number of treatments for both AFB and EFB are no longer available over-the-counter. The US Food and Drug Administration (FDA) is tightening up access to these antibiotics since there is strong evidence that their overuse is starting to limit their effectiveness. These drugs will be available only through prescription and only as a way to treat AFB/EFB, not for preventative purposes.


AFB is considered such a serious disease that many state apiary inspectors require infected hives to be burned! Other options may exist but the precise way to respond is complex and beyond the scope of this lesson. For many beekeepers, burning a hive and starting afresh is the only approach that will provide peace of mind that AFB spores are not present.

AFB is a devastating disease. The outcome is often as sad as this…

European Foulbrood


Serious though it is, European Foulbrood (EFB) is nowhere near as severe and damaging as AFB. However, it can still have very serious consequences for your bees.

EFB is caused by the bacterium Melissococcus plutonius. Like the AFB bacterium, it is ingested by larvae and then competes for food with the larvae. If the bacterium wins this battle, then the larvae will die.

While the bacterium does not create spores, EFB can stick around and potentially reappear each year. There is some evidence that bites by varroa mites (which already cause enough damage!) can also contribute to the spread of EFB within a colony.

There appears to be a relationship between the ratio of nurse bees to larvae and the incidence of EFB. As this ratio falls, EFB is more common. One situation where this can occur is the onset of the honey flow in early spring. The assignment of worker bee roles is highly dynamic throughout the year. With the increased availability of nectar, as the honey flow starts, bees will assign more workers to foraging. This, in turn, means fewer nurse bees, which can result in an outbreak of EFB.

This all means that EFB has a relationship with the honey flow. When the ratio of nurse bees to larvae recovers EFB will likely fall off.


Larvae attacked by EFB bacterium may lose the battle for food and die. The larvae will become curled, yellow to brown, and have a rubbery feel. A key difference with AFB is that the larvae die before the cell is capped.

When inspecting a hive, a spotty brood pattern can be a sign of EFB. This is not decisive, since many types of issues are evident through spotty brood patterns, but it can be a significant clue to EFB being present. The reason for the spotty pattern is that some of the larvae die before their cells are capped and workers won’t cap such a cell.

Determining whether a hive is infected with EFB can be difficult for the inexperienced beekeeper, due to the similarity in its symptoms with other problems. The first clues will be evident through visual inspection but accurate diagnosis is best done by state inspectors or by using diagnostic kits that are available.


As with many potential problems in beekeeping, the best way to avoid EFB is through a strong colony. Of particular note with EFB is a strong and productive queen. Therefore, requeening is sometimes justified as a way to prevent or resolve EFB.


The options for treatment of EFB are less dramatic than the burn-the-hive methods for AFB. Terramycin can be used, for example.

Some advocate the use of the “shook swarm” method, a curious technique that creates a “swarm” by shaking! The intent of this is to move the colony to new comb. Here is a video of that technique being illustrated to some new beekeepers.