American foulbrood (AFB)
The one bee disease every keeper fears — not because it kills a colony fast, but because there is no real cure, and the spores it leaves behind can infect the next colony housed in the same equipment years later.
- Cause
- Paenibacillus larvae (spores)
- Kills
- Capped larvae
- Spore survival
- Decades in old equipment
- Standard response
- Burn hive — no real cure
Overview
American foulbrood is caused by Paenibacillus larvae, a spore-forming bacterium that infects honeybee larvae. Young larvae swallow spores in their food; the bacteria multiply inside the larva, killing it after the cell is capped, and each dead larva can leave behind billions of new spores — an amount large enough to infect the entire colony and contaminate the comb and hive woodware for decades.
The classic sign is a patchy, irregular brood pattern with sunken, greasy-looking, often perforated cell cappings scattered among healthy capped brood. Opening a suspect cell reveals a dead larva that has turned brown and become a sticky, "ropey" mass that strings out several centimetres when drawn out with a matchstick — this ropiness test is the most reliable field check. A heavily infected comb also carries a distinctive foul smell, which is where the disease gets its name.
There is no antibiotic or treatment that reliably clears AFB spores from a colony and its equipment — spores are extraordinarily resistant to heat, drying and most disinfectants, and can remain infective in old comb or hive woodware for 40 years or more. Because of this, the standard and, in most beekeeping regions, legally required response to a confirmed case is to destroy the infected colony and burn its comb, frames and often the hive boxes, rather than attempt treatment.
This is a general guide, not a substitute for a veterinarian. Always call a vet for diagnosis, dosage and treatment of a sick animal.
Signs to look for
- A patchy, spotty brood pattern instead of the normal solid block of capped brood.
- Sunken, moist, greasy-looking cell cappings, often with an irregular perforation or hole in the centre.
- A dead, brown, sticky larva inside a suspect cell that "ropes" out several centimetres when drawn with a matchstick or twig — the single most reliable field test.
- A distinctive foul, glue-pot-like smell from heavily infected brood comb.
- Dried larval scales stuck firmly to the lower wall of the cell, hard to remove, in older infections.
- A colony that is otherwise active and bringing in stores can still be heavily infected — check brood pattern directly rather than judging by colony activity alone.
Confirming a suspect case
- Use the ropiness test on several suspect cells — insert a matchstick or twig into the dead larval remains and slowly withdraw it; a sticky, ropey thread several centimetres long is the classic AFB indicator.
- Compare against similar-looking but different diseases: European foulbrood and sacbrood can also cause dead, discoloured larvae, but neither typically ropes out the same way or leaves the same sunken, perforated cappings.
- When in doubt, do not guess — send a sample of suspect comb to a bee-disease diagnostic laboratory or apiary inspector for confirmation before deciding on destruction.
- Inspect neighbouring colonies in the same apiary once one case is confirmed, since robbing and drifting bees commonly spread it between nearby hives.
The standard response
- Confirmed AFB colonies are destroyed: the bees are killed, and the comb, frames and often the hive boxes themselves are burned — there is no reliable way to cure an infected colony and keep it.
- Bury the ashes deep, well away from any apiary, so spores in the residue cannot be picked up by foraging bees.
- Scorch the inside of any wooden hive parts that will be reused (never the comb) with a blowtorch until charred, as an extra safety margin — but when in doubt, burn rather than reuse.
- Never move frames, comb or honey from a suspect or confirmed AFB colony into another hive, and never feed suspect honey back to bees.
- Report a confirmed or strongly suspected case to the local beekeeping association or apiary inspection authority where one exists — AFB spreads between apiaries and neighbouring beekeepers need to know.
Preventing it in the first place
- Never buy or accept second-hand comb, frames or extracted equipment of unknown disease history — this is the commonest way AFB enters a clean apiary.
- Buy package bees, nucs or queens only from a reputable, disease-inspected source.
- Do not feed a colony honey from an unknown or suspect source, including harvested honey of uncertain origin — robbing out AFB-contaminated honey is a classic infection route.
- Inspect brood pattern regularly as part of routine hive checks, so a case is caught early, before it has spread heavily within the colony or to neighbours.
- Keep hive tools and gloves clean between colonies, and avoid moving frames between hives during routine inspections unless you are confident both are healthy.
Animals affected
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Frequently asked questions
Can I save a colony with American foulbrood by treating it with antibiotics?
Some antibiotics can suppress active symptoms temporarily, but they do not kill the resistant spores already in the colony and comb, so the disease typically returns, often after the antibiotic has also masked the signs long enough for it to spread further undetected. This is why destruction of the colony and comb, not antibiotic treatment, is the standard recommendation almost everywhere.
Is honey from an AFB-infected hive safe for people to eat?
Paenibacillus larvae is specific to honeybee larvae and is not known to cause illness in people, so honey itself is not considered a human health risk. The real danger of moving that honey around is to other bee colonies — feeding it to bees, or letting bees rob it out, is a very effective way to spread the spores to healthy hives, which is why suspect honey should never go back to any apiary.
Can I disinfect and reuse my hive boxes after burning the comb?
AFB spores are extremely resistant — ordinary washing or disinfectants do not reliably kill them on wood. Where reuse is attempted, the inside of wooden boxes is scorched with a blowtorch until charred as an extra safety step, but frames and comb are always burned, never reused. When in doubt, burning the whole hive is the safer choice; a repeat outbreak from contaminated equipment is far costlier than a new set of boxes.
How is American foulbrood different from the wax moth damage I sometimes see in stored comb?
They are unrelated problems. Wax moth is an insect pest that tunnels through and webs over comb, mostly in weak colonies or improperly stored spare comb, and is managed by keeping colonies strong and storing comb in a lit, ventilated space. AFB is a bacterial disease that kills brood inside capped cells and requires destroying infected equipment — the ropy-larva test and the perforated-capping pattern are what tell the two apart.
Signs, prevention and treatment follow ICAR, DAHD and state veterinary-university practice; vaccine schedules are the commonly notified ones and may vary by region or outbreak status. Always confirm with a veterinarian before treating an animal. editorial policy.