Honey bees are essential to our agricultural system, playing a critical role in the pollination process of 85% of our crops. However, these industrious insects face several threats. Among some of these threats are bacterial diseases such as foulbrood (the name is associated with a foul odor) that target young bees. There are 2 types of foulbroods: American foulbrood (AFB) and European foulbrood (EFB). Whether you’re a seasoned beekeeper or just starting, understanding these diseases is crucial to maintaining healthy hives.

American Foulbrood (AFB)

What is it?

AFB is a lethal bacterial disease caused by a spore-forming bacterium called Paenibacillus larvae that negatively affects the brood (undeveloped bees) in bee colonies. It targets honey bee larvae and pupae, and is considered one of the most serious diseases affecting bee colonies worldwide.

How Does it Spread?

The disease begins when nurse bees feed young larvae with food contaminated with spores from Paenibacillus larvae. These spores are incredibly resilient and can survive for decades. Once ingested, the spores germinate in the larva’s gut, multiply rapidly, and lead to the larva’s death, typically just before or during the pupal stage.

The dead larva turns into a coffee-brown color and breaks down into a sticky, gooey mass. Housecleaning bees attempting to remove this decaying material inadvertently spread the spores throughout the hive. These spores can end up in honey stores or be passed to new larvae, accelerating the spread of the disease.

One of the major ways AFB spreads between colonies is through robbing behavior. Bees from nearby hives may rob honey from infected colonies and carry spore-laced honey back to their hives, infecting their young in the process. Other methods of infection are contaminated equipment, frames, and feed.

How to Detect It?

AFB can be detected using the “rope test.” Simply insert a thin stick or twig into a cell with suspicious brown goo. Stir slightly and slowly pull it out. If the substance ropes out in a threadlike manner, it is a strong indicator of AFB. If you are not sure if your colonies are infected, please contact your beekeeper inspector for confirmation. You can find your local beekeeper inspector here.

Treatment

Unfortunately, there is no effective cure for AFB. The only effective way to stop its spread is by burning the infected hive and equipment, which is required by law to do so when diagnosed. Chemical treatments may suppress symptoms temporarily, but the resilient spores remain and can cause future outbreaks.

European Foulbrood (EFB)

What is it?

Similar to AFB, EFB is another serious brood disease. EFB is caused by a non-spore-forming bacterium called Melissococcus plutonius. While less deadly than AFB, it still poses a significant threat to colonies, especially during times of stress or poor nutrition.

How Does it Spread?

EFB primarily affects larvae that are less than 4-5 days old. These infected larvae turn yellow-brown and usually die while still curled at the bottom of their cells. Compared to AFB, this disease typically kills uncapped larvae rather than pupae. The disease often appears in early spring and, to a lesser extent, in autumn.

The bacteria multiply in the larval gut after the bee is fed contaminated food. Stressful conditions like poor nutrition, overcrowding, or insecticide exposure can trigger outbreaks.

Just like AFB, EFB can be spread by robbing infected bees, contaminated hive equipment, transferring infected honeycomb or supers, and feeding bees infected honey or pollen.

How to Detect It?

Infected larvae change color, first turning yellow and then brown. The disease is often confused with AFB, but larvae affected by EFB typically die earlier in development and do not rope when tested.

Treatment

Unlike AFB, EFB can sometimes be managed without destroying the hive. With improved nutrition, reduced stress, and sometimes the use of approved antibiotics (where legal), colonies can recover rapidly. However, vigilance is key. Ongoing monitoring is essential to prevent reinfection.

Conclusion

Both AFB and EFB are serious threats to honey bee colonies, but they differ significantly in terms of treatment and impact. Knowing the symptoms, methods of transmission, and appropriate responses can make all the difference in keeping your hives healthy. Regular hive inspections, good hive hygiene, and early detection are your best defenses. Remember, when it comes to foulbrood, prevention and awareness are the beekeeper’s most powerful tools.

For more information about foulbrood diseases in honey bees, read the “Ask IFAS” publication called: “Identification and Treatment of European Foulbrood in Honey Bee Colonies.”

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