American and European Foulbrood in Honeybees: How to Spot It Before It Spreads

Foulbrood bees are one of the most worrying things a beekeeper can find during a hive inspection, and the name covers two very different diseases. American foulbrood disease is caused by a spore-forming bacterium that can survive on hive equipment for decades, while European foulbrood is a milder infection that colonies sometimes recover from. 

Knowing which one you are dealing with early decides whether you manage a problem or lose a colony and the equipment around it. This guide explains how the two diseases differ, what American foulbrood looks like, how to test for it, how common it really is, what can and cannot be treated, and how to keep it out of your apiary.

Do Bees Carry Diseases?

Yes, honey bees can carry bacteria, viruses, fungi, and parasites, which is why the wider category of bee diseases includes everything from foulbrood to Nosema to the viruses that mites spread. Foulbrood affects bees only and does not infect people. Honey from an affected hive is not a danger to humans, but it can carry spores that infect bees, which is one reason to avoid feeding colonies honey of unknown origin. Mites are a separate threat that weakens colonies and leaves them more vulnerable to other problems, so a mite plan from the Varroa mite control range belongs in any disease prevention routine alongside the brood checks described below.

What Is Foulbrood Disease in Bees?

Foulbrood disease is a group of bacterial infections that attack honey bee brood, meaning the developing larvae and pupae, rather than adult bees. The two forms are American foulbrood (AFB), caused by the bacterium Paenibacillus larvae, and European foulbrood (EFB), caused by Melissococcus plutonius. Both kill brood, and a colony that loses brood weakens quickly because fewer young bees are raised to replace the workers that age out.

AFB is considered the most serious bacterial disease of honey bee brood because of the spores it produces. A single infected larva can produce more than a billion spores, and a young larva can become infected by only a few dozen of them. The spores can stay viable on beekeeping equipment for decades, and sources vary on exactly how long, which is why the practical advice is to assume that contaminated equipment stays contaminated.

Foulbrood also spreads in very ordinary ways. Robbing bees carry spores from a weak infected colony into healthy ones, drifting bees move between hives, and shared frames, boxes, and tools carry spores from one apiary to the next.

What Are the Main Differences Between American Foulbrood and European Foulbrood in Bees?

American foulbrood is caused by a spore-forming bacterium and usually kills larvae after their cells are capped, while European foulbrood is caused by a bacterium that does not form long-lived spores and usually kills larvae before capping. AFB is the more destructive of the two, and colonies sometimes recover from EFB.

Because the signs overlap, a field diagnosis is only a starting point. The two diseases can look similar to the untrained eye, so confirmation by a bee inspector or a laboratory protects you from destroying a colony that did not need it and from keeping one that should go.

What Does European Foulbrood Look Like?

European foulbrood is easy to confuse with American foulbrood, so it helps to know its own signs. Because EFB infects young larvae, most of the damage shows up before the cells are capped, and the first thing many beekeepers notice is a patchy brood pattern with larvae that look wrong in open cells.

• Larvae: Dead or dying larvae turn yellow to brown and often lie twisted or curled in the cell instead of resting in their normal coiled position.

• Scale: The dried remains form a rubbery scale that comes out of the cell more easily than an AFB scale.

• Odor: A sour smell is more typical than the glue pot odor of AFB.

• Rope test: The matchstick test gives little or no rope, which is one of the quickest ways to separate EFB from AFB in the field.

Because the bacterium does not form long-lived spores, EFB is less persistent on equipment, but it can return in later seasons. A confirmed diagnosis from an inspector or lab is still the right next step, since the signs of the two diseases overlap and the response to each is different.

How to Identify American Foulbrood

Most beekeepers spot trouble during a brood inspection, which is why it pays to look closely at the brood frames every time you open a hive. Healthy brood shows solid, flat, evenly colored cappings with pearly white larvae underneath. Anything that breaks that pattern deserves a closer look before you move any frame to another hive.

What Does American Foulbrood Look Like?

• Cappings: Cells look sunken and darker than healthy cappings, and many have small ragged holes where the bees have chewed through them.

• Brood: Larvae and pupae turn brown or black instead of staying glistening white, and they lose their shape as they decay.

• Scale: Dead larvae dry into a dark, brittle crust on the lower wall of the cell that is very hard to remove. Hold the frame so sunlight falls along the cell floors, because scale is easy to miss when you look straight into the cells.

• Odor: A characteristic smell often described as a glue pot. It is easier to notice in advanced cases.

• Moisture: In heavily infected colonies, decaying brood can ooze moisture onto the comb surface.

How to Test for American Foulbrood in the Hive

Here are some ways you can test your colony for American Foulbrood:

1. Rope test: Push a matchstick or small twig into a suspect cell, stir the contents, and draw the stick out slowly. Brown larval remains from an AFB infection stretch into a thin, elastic thread. It is a strong indicator, but it is not completely conclusive on its own.

2. Lateral flow test kit: Field kits made for AFB react to the bacterium and give a quick answer. They are sold through beekeeping suppliers and are a useful second check.

3. Holst milk test: Swirl a sample of scale or an affected pupa in a weak skim milk solution. If the milk clears, AFB is suspected. EFB gives a negative result.

4. Inspector or lab confirmation: Contact your state apiarist or local extension office. AFB must be reported in many places, and an official diagnosis protects you from acting on a look-alike condition.

Keep your equipment clean during any suspect inspection. A dedicated hive tool for a suspect colony, disinfected before it touches another hive, costs far less than carrying spores into a healthy one. Soap and water do not remove spores from gloves, so consider keeping a spare pair of beekeeping gloves for diseased or suspect colonies.

How Common Is American Foulbrood?

American foulbrood (AFB) is relatively uncommon as an active disease, but the spores that cause it are much more widespread. For example, a 2015 survey in Utah inspected 854 bee colonies and found AFB in just 3, representing less than 1%.

However, a separate study of bee colonies used for almond pollination in California found AFB spores in approximately 70–80% of the beekeeping operations sampled. Around 4% of the colonies had spore levels high enough to raise concerns about developing the disease without preventive measures.

For beekeepers, this means that while you may never encounter an active AFB infection, the spores can still be present in the beekeeping environment. Poor hive management, contaminated equipment, and moving infected frames between colonies can increase the risk of an outbreak.

These findings come from specific regions and time periods, so infection rates may differ depending on your location. For information about AFB activity in your area, contact your local or state apiary inspection program.

How Does Foulbrood Affect Bee Colonies and Honey Production?

Foulbrood affects developing bees, making it difficult for a colony to maintain a healthy population. As older worker bees die, fewer young bees are available to replace them, causing the colony to gradually weaken. Over time, it becomes harder for the bees to defend their hive, collect food, and survive. In cases of American foulbrood, an untreated colony will typically continue to decline and may eventually die.

As the bee population decreases, honey production also suffers. With fewer foragers collecting nectar, the colony struggles to produce surplus honey. However, a bigger concern is the spread of infection. When worker bees remove dead larvae, they can spread foulbrood spores throughout the hive, including into stored honey. Infected honey frames can also introduce spores into healthy colonies if they are transferred between hives or exposed to robbing bees.

Robbing is especially dangerous for weak, infected colonies. Bees from stronger colonies may enter these hives to steal honey and unknowingly carry spores back to their own colonies, spreading the disease further. To help reduce this risk, Blythewood's guide to robbing screens in the fall explains when installing an entrance screen can help protect vulnerable hives.

Can You Recommend Treatments for Foulbrood in Bees?

Treatment depends on which foulbrood you have, and the two diseases are handled very differently.

• American foulbrood: There is no cure. Antibiotics do not kill spores, and they can hide visible symptoms while spores continue to spread. Many regions require infected colonies to be reported and destroyed, usually by burning, so contact your state apiarist before taking action on your own.

• European foulbrood: Colonies sometimes recover on their own. When treatment is needed in the United States, antibiotics such as oxytetracycline are only available with a veterinary feed directive from a licensed veterinarian. So work with your inspector, extension office, or vet on a plan.

• Equipment: Contaminated beekeeping equipment must be carefully treated to prevent the disease from spreading. Common methods include scorching wooden hive boxes, burning infected frames and comb, and disinfecting tools. In some countries, gamma irradiation is also used to sterilize equipment. This process leaves no chemical residue and allows equipment to be reused once treatment is complete and it has been cleared for use.

Does Bleach Kill American Foulbrood?

It can, but only on the right equipment under the right conditions. The UK National Bee Unit reports that soaking cleaned hive tools and other non-wood equipment for 20 minutes in a 0.5 percent sodium hypochlorite solution kills AFB spores. Household bleach contains about 3 percent sodium hypochlorite, so that works out to roughly one part bleach to six parts water.

Bleach is not a dependable fix for wooden boxes and frames, because spores can hide in cracks, wax, and propolis. Scorching with a blowlamp is the usual method for wooden boxes, and frames with comb are normally burned. Some jurisdictions, including Australia, do not accept bleach for AFB at all, so follow local rules. Rinse metal thoroughly afterward because bleach corrodes it, work in a ventilated area, and never mix bleach with other cleaners.

How to Prevent American Foulbrood

Prevention is the only dependable strategy, since there is no cure once spores are established in equipment.

• Inspect brood regularly: Look at brood frames on every inspection, and work through a routine such as Blythewood's end-of-season inspection checklist so nothing is skipped before winter.

• Keep colonies strong and block robbing: Strong colonies defend themselves better, and entrance screens and reduced entrances limit the chances for spores to travel between hives.

• Vet used equipment and new colonies: Avoid secondhand boxes and frames unless you know their history, and inspect swarms and new colonies before you place them near others. Starting from inspected nucleus hives reduces the chance of bringing in a hidden problem.

• Rotate out old brood comb: Replacing old comb every few years removes places where spores and other problems build up. A stock of fresh frames and foundation makes that rotation easy.

• Disinfect tools between hives: Clean your hive tool between colonies, and do not move frames or boxes between hives unless you have inspected the brood.

• Clean shared extractors properly: A soda crystal wash kills EFB but not AFB spores, so a third wash with diluted bleach is recommended if there is any concern about disease in the area. Rinse well afterward.

• Avoid feeding honey of unknown origin: Honey from sources you cannot trace may carry spores, so feed sugar syrup instead of unknown honey.

If you suspect AFB, close the hive, avoid moving frames or equipment between colonies, and call your state apiarist or local extension office for confirmation. Catching a problem early protects the rest of your apiary. For routine upkeep supplies, the hive maintenance collection covers the tools and parts you will need for regular inspections.

Conclusion

Foulbrood is serious, but it is manageable when it is caught early and when equipment is handled with care. American foulbrood is the one to take most seriously because its spores last for decades and it has no cure, while European foulbrood is milder and colonies sometimes recover. Regular brood inspections, clean tools, strong colonies, and honest local reporting protect an apiary better than any single product.

Blythewood Bee Company stocks the supplies that make those habits easier. You can find hive tools and frame grips for clean inspections, fresh frames and foundation for rotating out old comb, and the full pest control category for mite management that keeps colonies strong enough to resist disease.

Frequently Asked Questions

What are the main differences between American foulbrood and European foulbrood in bees?

American foulbrood is caused by a spore-forming bacterium, kills larvae mostly after capping, and is usually fatal to the colony. European foulbrood is caused by a non-spore-forming bacterium, kills larvae mostly before capping, and colonies sometimes recover from it.

Do bees carry diseases?

Yes. Honey bees can carry bacteria, viruses, fungi, and parasites. Foulbrood affects bees only and does not infect people, but contaminated honey and equipment can spread it between colonies.

How common is American foulbrood?

Active cases are uncommon, with surveys such as one in Utah finding it in well under one percent of inspected colonies. Spores are far more widespread than visible disease, so prevention still matters.

Does bleach kill American foulbrood?

It can be used to clean hive tools and other non-wood equipment when soaked for 20 minutes in a 0.5 percent sodium hypochlorite solution. It is not reliable for wooden boxes and frames, and some regions do not accept it, so follow local rules.

Can you recommend treatments for foulbrood in bees?

American foulbrood has no cure, and many regions require reporting and burning of infected colonies. European foulbrood sometimes clears on its own, and any antibiotic use in the United States requires a veterinary feed directive.