American and European Foulbrood: Spotting and Reporting

Foulbrood is a bacterial infection of bee larvae, and it's one of the few hive problems that can genuinely threaten beekeepers beyond your own yard. American foulbrood (AFB) is the more serious of the two: its spores are nearly indestructible, persist in wood for decades, and have no practical cure once a colony is infected. In many countries, states, and provinces, AFB is a notifiable disease, meaning you are legally required to report a suspected case to your state or provincial apiary inspector. Knowing how to tell the two diseases apart, and what to do next, is something every beekeeper should learn before they ever need it.

What Is American Foulbrood?

American foulbrood is caused by the bacterium Paenibacillus larvae. The name is misleading, it was identified in the United States but it exists worldwide. The bacterium itself is not the direct killer; the spores are. A single infected larva can contain billions of spores, and those spores survive boiling, most disinfectants, and decades of sitting in old comb or woodenware.

Young larvae ingest spores through contaminated food. The bacteria germinate in the larval gut, multiply, and kill the larva after it has been capped. By the time you see symptoms, the infection has usually been spreading for weeks.

There is no registered antibiotic treatment that eliminates spores from a hive. Oxytetracycline (Terramycin) was used historically to suppress vegetative bacteria, but it does nothing to spores already in the wax and wood, so colonies relapse. Most apiary authorities around the world now advise destruction of infected colonies and equipment by burning. That is a hard thing to do, but it's the reason early detection matters so much.

What Is European Foulbrood?

European foulbrood is caused by Melissococcus plutonius and behaves quite differently. It kills larvae before capping rather than after, so the visual signs show up in open cells. EFB is associated with stress: hives that are short on food, heavily varroa-loaded, or dealing with a disrupted laying pattern are more susceptible.

Unlike AFB, EFB can sometimes clear on its own when the underlying stress is removed and the colony's population surges. Strong nectar flows, requeening with a hygienic or locally adapted queen, and getting varroa under control (see managing varroa mites) often allow a colony to recover. In some jurisdictions, antibiotic treatment is permitted for EFB. Check with your apiary inspector before treating either disease, the rules vary by location.

Comparing AFB and EFB at a Glance

Feature	American Foulbrood (AFB)	European Foulbrood (EFB)
Causative organism	Paenibacillus larvae (spore-forming)	Melissococcus plutonius (non-spore)
Stage killed	Capped larvae (pupae)	Uncapped larvae
Cell cappings	Sunken, greasy, perforated	May be present but removed by bees
Larva color	Brown to black; coffee-colored "goo"	Yellow to brown; twisted in cell
Larva position	Melted flat along bottom of cell	Often twisted or lying on side
Rope test	Stretches 1–3 cm (positive)	Does not rope (negative)
Smell	Sour, rotting glue; very pungent	Sour/vinegary; less severe
Treatment	Destruction of colony + equipment	Sometimes resolves; treatment varies by region
Reportable?	Yes, in most jurisdictions	Varies by jurisdiction

Visual Signs to Look For

Walk through your brood nest slowly and methodically. A healthy brood frame has a tight, uniform pattern: capped cells dome slightly, are a consistent tan color, and show no perforations. Foulbrood disrupts that pattern in characteristic ways.

Signs of American Foulbrood:

• Spotty, irregular brood pattern (bees have been removing some cells but can't keep up)
• Cappings that look sunken, darker than normal, and slightly wet or greasy
• Small holes chewed in cappings where bees attempted to remove a dead larva
• Inside the cells: a coffee-brown, stringy mess instead of a healthy white pupa
• A penetrating smell, often described as rotting glue or rotten sneakers, you may notice it before you open the hive
• Scale (dried remains) stuck flat along the lower cell wall, often with the tongue visible

Signs of European Foulbrood:

• Dead or dying larvae in uncapped cells, often yellow-brown and twisted
• A mottled brood pattern with healthy cells beside visibly unhealthy ones
• A sour smell, but usually less severe than AFB
• Larvae may look "melted" but will not rope

The Rope Test (and When to Use It)

The rope test, sometimes called the matchstick test, is the standard field check for AFB. It does not replace laboratory confirmation, but it gives you an immediate data point.

Take a small twig, toothpick, or matchstick and insert it gently into a suspect capped cell. Stir slightly, then slowly withdraw the stick. If the cell contains AFB-killed larvae, the liquefied remains will stretch into a sticky, elastic thread 1–3 centimeters long before snapping. This ropy, caramel-like consistency is the defining field sign of AFB.

EFB does not produce a rope. The remains are drier or granular in texture and break immediately.

A positive rope test is strong evidence of AFB, but it's not definitive on its own. You need your inspector to confirm. Do not take any action based solely on a field test, get a professional to look at the hive.

Why AFB Usually Means Destruction

This is the part beekeepers find hardest to accept. The spores of P. larvae are among the most durable biological structures known. They survive in old comb for 40 years or more. They survive most bleach solutions at practical concentrations. Flame sterilization of woodenware is possible in theory, but the margin for error is slim and most regulatory authorities don't consider it reliable enough.

The practical consequence: once AFB is confirmed in a hive, the frames, comb, and often the wooden boxes have to be burned. In some jurisdictions this is a legal requirement, not a recommendation. The bees are killed before burning to prevent them from carrying spores to neighboring hives. Honey from an AFB hive must not be fed to bees (though it is generally considered safe for human consumption, which is covered in the FAQ below).

This sounds extreme, but consider the alternative. A hive with AFB that robbing bees visit, or from which you unknowingly sell or give away frames, can seed infections across an entire local beekeeping community. The spores in one frame of comb can cause dozens of colonies to collapse over the following years.

Your Legal Duty to Report

In most of the United States, Canada, Australia, the United Kingdom, and much of Europe, AFB is a notifiable disease. That means you have a legal obligation to report a suspected case to your state or provincial apiary inspector. Failing to report can result in fines, and more practically, it can allow an outbreak to spread to neighboring beekeepers who have no idea their hives are at risk.

EFB reporting requirements vary more by jurisdiction. Some regions require notification; others treat it as a management problem.

If you suspect either disease, do the following:

1. Stop moving frames, bees, or equipment away from the hive.
2. Contact your state or provincial apiary inspector immediately.
3. Do not attempt treatment, destruction, or any other action until the inspector has examined and confirmed the diagnosis.
4. Keep the hive closed as much as possible to limit robbing.

Your inspector will usually visit within a few days, take samples for laboratory testing, confirm the diagnosis, and advise you on your legal obligations regarding destruction or treatment. In some regions, inspectors can order destruction and the process is mandatory; in others, it's advisory. Either way, they are your first call.

Prevention

You cannot fully prevent foulbrood, but you can reduce your risk significantly.

• Never move frames between hives of unknown health status. This is the single most common way AFB spreads between colonies.
• Buy bees from reputable sources. Ask suppliers whether their hives have been inspected and are free of notifiable diseases.
• Inspect regularly. Catching a case early, before the colony has collapsed and been robbed out, limits the spore load that escapes.
• Keep colonies strong. A large, well-fed population can remove some infected cells before the disease spreads. EFB in particular tracks with stress and varroa load, control mites (a mite wash is a good monitoring starting point) and provide adequate forage.
• Don't feed honey of unknown origin. Shop-bought honey can contain AFB spores if it was processed from infected hives; feeding it to bees is a documented route of introduction.
• Use new or thoroughly sourced equipment. Old secondhand hive bodies can carry spores. If you're buying used gear, have it inspected or treat it with flame if your inspector agrees.

Managing overall colony health, including staying on top of nosema, keeps colonies in better condition to resist opportunistic diseases.

---

Frequently Asked Questions

How do I know it's AFB and not EFB?

The rope test is the fastest field indicator: AFB ropey remains stretch 1–3 cm on withdrawal; EFB does not. The stage at which larvae die is also telling, AFB kills capped pupae, EFB kills open larvae. Smell can help too, since AFB has a distinctively pungent, penetrating odor. That said, field signs can overlap, and a laboratory test using a sample sent to your state or provincial apiary inspector is the only way to confirm the diagnosis. Don't guess and act, call your inspector.

Can foulbrood be cured?

EFB sometimes resolves on its own when the stressor is removed (poor nutrition, varroa, a weak queen). Some jurisdictions permit antibiotic treatment for EFB. AFB has no practical cure. Antibiotics suppress the vegetative bacteria but do not kill spores, and colonies relapse. Once AFB is confirmed, destruction of the colony and infected equipment is the standard response in almost every regulatory system.

Do I have to report it?

For AFB: yes, in the vast majority of jurisdictions in the US, Canada, UK, Australia, and Europe. It is a notifiable disease. For EFB: it depends on where you are. When in doubt, report it anyway, your apiary inspector will tell you if it's not required in your area. There is no penalty for reporting a suspected case that turns out to be something else; there can be penalties for not reporting a confirmed one.

Can it spread to my other hives?

Yes, easily. Robber bees from nearby colonies will take honey and spores from a collapsing AFB hive back to their own. Any frames, tools, or gloves that contact infected material can carry spores. If you suspect AFB in one hive, treat all your equipment as potentially contaminated and stop moving anything until you've spoken to your inspector.

Is honey from an AFB hive safe to eat?

For humans, yes, P. larvae does not infect people, and cooking destroys the vegetative bacteria. However, honey from an AFB hive must never be fed to bees. Even processed, store-bought honey can carry viable spores if it came from infected colonies, which is one reason feeding bees honey from unknown sources is always a risk. Extract your honey elsewhere, away from the hive, and do not allow bees access to the wet supers if AFB is present.