American foulbrood

American foulbrood (AFB) is the most serious bacterial disease of honey bee brood. It only affects larvae, but an infected colony almost always dies in the end, and the disease passes easily from hive to hive and from apiary to apiary. It is present on almost every continent.

It is harmless to people: the honey is safe to eat, but must never be fed to bees, because it can carry huge numbers of spores. This page covers the biology of the bacterium, the symptoms, diagnosis, French regulations and what to do.

The agent: a spore-forming bacterium

Paenibacillus larvae produces spores, highly durable resting forms. Only the spores are infectious: the active form of the bacterium does not transmit the disease¹. A single larva killed by AFB can contain more than a billion of them².

According to the WOAH manual, spores survive 3 to 10 years in honey, wax, dead larvae and the environment, about 35 years in dry scales, and more than 70 years when purified².

An infection that only strikes very young larvae

Nurse bees infect larvae by feeding them food contaminated with spores. Susceptibility drops very quickly with age. In trials on laboratory-reared larvae, larvae aged 24 to 28 hours were the most susceptible: the dose killing half of them was about eight spores. Older larvae became markedly more resistant⁵. Beyond about 53 hours after hatching, a larva can no longer be infected². Adult bees never fall ill, but they carry the spores.

The spores germinate in the gut, the bacteria multiply there and then invade the whole body. The larva usually dies after capping, at the prepupal or pupal stage, and turns into a brown, sticky mass loaded with spores¹.

ERIC genotypes

Since 2006, P. larvae is no longer divided into subspecies⁶. Strains are classified into ERIC genotypes, based on a genetic fingerprinting method. Four genotypes, ERIC I to IV, were described first; a fifth, ERIC V, was isolated in 2020 from Spanish honey⁸.

Only ERIC I and ERIC II are commonly found in the field. They do not kill larvae at the same speed: in the laboratory, ERIC I takes about 12 days to kill all infected larvae, against about 7 days for ERIC II. The rare genotypes kill in about 3 days⁸. Paradoxically, a fast strain is often less dangerous for the colony: larvae die before capping and the workers remove them. A slow strain lets larvae die under the capping, where they produce more spores⁷. In France, the national reference laboratory performs this genotyping for epidemiological investigations¹¹.

How it spreads

• Robbing of a sick or dead colony: the main route between apiaries.
• Swapping frames, supers or equipment between hives.
• Feeding honey of unknown origin.
• Buying unchecked colonies or second-hand equipment.
• Drifting bees between neighbouring hives.
• The beekeeper, via gloves and hive tool.

Why it is so serious

An infected colony does not recover by itself. Each dead larva becomes a reservoir of spores, which house bees spread as they clean out the cell. The affected brood expands, the colony weakens, then it is robbed, which carries the spores to other colonies. No treatment destroys the spores, and equipment stays contaminated for years. This is why most countries list AFB as a regulated disease and impose collective measures³.

Recognising American foulbrood

At first, only a few cells are affected, and frames must be checked one by one to find them¹². Typical signs are:

• Spotty brood: empty, capped and open cells mixed together.
• Abnormal cappings: sunken, darker, greasy or moist-looking, often pierced with a small irregular hole.
• Cell contents: larva or pupa turning light brown then chocolate-brown, shapeless and sticky.
• Scale: the larva dries into a black scale, stuck to the lower wall of the cell, very hard to remove and infectious⁴.
• Pupal “tongue”: a thread stretched towards the top of the cell. A very typical sign, but rarely seen⁴.
• Smell: strong in advanced cases, described as ammonia-like or glue-like¹².
• Weakened colony, with little activity at the entrance.

The rope test

Push a dry matchstick or twig into a suspect cell, stir the contents, then pull it out slowly. With AFB, the contents stretch into a brown, elastic thread, longer than about 2 cm according to beekeeping guides¹².

The test points the way; it does not confirm. It does not work on dry scales, and very watery remains can give a false negative^{2, 12}. Use one matchstick per cell, then burn it.

Do not confuse with

Diagnosis

Rapid field tests

Rapid strip tests, working like a pregnancy test, are sold for AFB. The contents of a cell, mixed with a buffer, are placed on the strip; the result can be read within minutes². A negative result does not rule out the disease. According to a 2024 study, their sensitivity for AFB has not been published; molecular field tests are being developed¹⁰. In France, a rapid test replaces neither the report nor the official analysis.

Laboratory analysis

Only a laboratory analysis confirms the disease. Reference methods are microscopy, bacterial culture and PCR; ERIC genotyping is used for investigations².

The sample. A piece of brood comb of about 10 × 10 cm, taken where abnormalities are most numerous¹², wrapped in paper rather than plastic and kept cool².

Where to send it in France. After a report, the DDPP, or the veterinarian it appoints, organises sampling and shipment to an approved laboratory. The national reference laboratory is the Anses laboratory in Sophia-Antipolis: it oversees this network, carries out specialised analyses and confirms cases where no approved laboratory exists¹¹.

Regulations in France

In France, AFB is classified as a first-category health hazard by the order of 29 July 2013. Under the European Animal Health Law (Regulation (EU) 2016/429), it falls into categories D and E, which require surveillance and rules for bee movements^{11, 12, 13}.

Reporting is mandatory. Any suspicion must be reported without delay to the departmental directorate for the protection of populations (DDPP), directly or through one’s veterinarian or beekeepers’ health organisation. Failing to comply with the prescribed measures can lead to criminal penalties and the loss of compensation¹³.

Measures are set by prefectoral order, under the ministerial order of 23 December 2009 on health policing of bee diseases. Their content varies case by case. For example, recent orders include¹³:

• placing the suspect apiary under surveillance, then an infection order if the laboratory confirms;
• a protection zone of 3 km around the outbreak and a surveillance zone of 2 km beyond it;
• a ban on moving hives, bees, queens, equipment and hive products in these zones, unless the DDPP grants an exemption;
• a census of apiaries and inspection by an appointed veterinarian, with sampling if needed;
• destruction of affected colonies or shaking them onto new equipment, then disinfection or destruction of the equipment;
• lifting of the measures only after clean-up and confirmation that the disease has disappeared.

The State may compensate for colonies and equipment destroyed on official orders. Rules differ between countries: elsewhere, check with your national veterinary services.

Control and what to do

Destroy or shake

The decision is made with the veterinary services.

Destruction applies to weak, heavily infected colonies, or those found late in the season. The bees are killed in the evening, once all foragers are home. Bees, frames, brood and stores are then burned or incinerated¹².

Shaking, or the shook swarm method, can save a strong, lightly infected colony if the season allows. The bees are shaken into a clean hive, onto new foundation, and all old frames are destroyed^{4, 12}. A Canadian study showed that colonies shaken onto foundation only had no further symptoms, whereas those shaken onto drawn comb kept light, transient infections. Put back on their old combs, they eventually died⁹.

Antibiotics: banned in the EU

In the European Union, no veterinary medicine is authorised to treat AFB⁴. In other countries, including the United States, antibiotics can be prescribed by a veterinarian. They mask the symptoms but do not destroy the spores: the disease returns as soon as treatment stops, and residues can end up in the honey^{1, 12}.

Disinfecting equipment

Frames, wax and stores are destroyed. Sound boxes, floors and roofs can be recovered after disinfection. See also Disinfecting equipment.

1. Scraping: remove wax, propolis and debris, then burn them.
2. Scorching all inner surfaces with a blowtorch until the wood turns lightly brown. This is the most common method.
3. Other recognised methods: hot caustic soda solution, bleach, or dipping in a bath of very hot microcrystalline wax^{4, 12}. These methods need suitable equipment and protection.
4. Small equipment: metal tools scorched; gloves and fabrics washed hot or destroyed. Cracked or porous wood disinfects poorly: better to burn it.

Prevention

• Inspect the brood at every spring and summer visit.
• Only buy colonies and second-hand equipment from reliable sources, and never feed honey of unknown origin.
• Close and examine any dead hive quickly.
• Replace brood combs regularly and limit frame swaps between apiaries.
• Favour lines with good hygienic behaviour, which detect and remove diseased larvae¹. See also Apiary biosecurity.

Most common mistakes

• Waiting to see instead of reporting: meanwhile, robbing spreads the spores.
• Moving or uniting a suspect colony with another.
• Reusing frames from a dead colony without knowing what killed it.
• Botching a shook swarm: drawn comb reused, or old equipment not disinfected.
• Believing a negative rapid test rules out the disease.
• Using imported antibiotics: illegal in the EU, useless against spores and a source of residues.

Frequently asked questions

Can you eat honey from an infected hive? Yes. The bacterium does not affect people. This honey must simply never be fed to bees or left open to robbing.

Can a colony recover on its own? Very rarely. A highly hygienic colony may contain a light infection, but once symptoms are visible, the outcome is almost always fatal.

Is shaking always enough? No. It only suits strong, lightly infected colonies, early in the season, and only onto new foundation. The brood must then be monitored for several months. In France, the prefectoral order and the veterinarian decide.

Should I report if the rope test is doubtful? Yes. You report a suspicion, not a certainty: the analysis settles it.

References

1. Genersch E. (2010). American Foulbrood in honeybees and its causative agent, Paenibacillus larvae. Journal of Invertebrate Pathology 103: S10-S19. doi.org
2. WOAH. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, chapter 3.2.2: American foulbrood of honey bees (version adopted 2016). woah.org
3. WOAH. Terrestrial Animal Health Code, chapter 9.2: Infection of honey bees with Paenibacillus larvae. woah.org
4. IZSVe, reference laboratory for honey bee health. American foulbrood factsheet. izsvenezie.com
5. Brødsgaard C.J., Ritter W., Hansen H. (1998). Response of in vitro reared honey bee larvae to various doses of Paenibacillus larvae larvae spores. Apidologie 29(6): 569-578. doi.org
6. Genersch E., Forsgren E., Pentikäinen J., Ashiralieva A., Rauch S., Kilwinski J., Fries I. (2006). Reclassification of Paenibacillus larvae subsp. pulvifaciens and Paenibacillus larvae subsp. larvae as Paenibacillus larvae without subspecies differentiation. International Journal of Systematic and Evolutionary Microbiology 56(3): 501-511. doi.org
7. Rauch S., Ashiralieva A., Hedtke K., Genersch E. (2009). Negative correlation between individual-insect-level virulence and colony-level virulence of Paenibacillus larvae, the etiological agent of American foulbrood of honeybees. Applied and Environmental Microbiology 75(10): 3344-3347. doi.org
8. Beims H., Bunk B., Erler S., Mohr K.I., Spröer C., Pradella S., Günther G., Rohde M., von der Ohe W., Steinert M. (2020). Discovery of Paenibacillus larvae ERIC V: phenotypic and genomic comparison to genotypes ERIC I-IV reveal different inventories of virulence factors which correlate with epidemiological prevalences of American Foulbrood. International Journal of Medical Microbiology 310(2): 151394. doi.org
9. Pernal S.F., Albright R.L., Melathopoulos A.P. (2008). Evaluation of the shaking technique for the economic management of American foulbrood disease of honey bees (Hymenoptera: Apidae). Journal of Economic Entomology 101(4): 1095-1104. doi.org
10. Ackerly D., Tran L., Beddoe T. (2024). The development of a loop-mediated isothermal amplification (LAMP) assay to detect American foulbrood in managed honey bee populations. Apidologie 55: 38. doi.org
11. Anses, National Reference Laboratory for Bee Health, Sophia-Antipolis. Annual activity report 2025 (in French). anses.fr
12. FNOSAD. Practical sheet no. 7: What is American foulbrood? (in French). fnosad-lsa.fr
13. Prefecture of Vaucluse (2024). Prefectoral order no. SSPAE 20240919-1 setting a restricted zone around an American foulbrood outbreak (example of measures, in French). saintsaturninlesapt.fr
14. USDA Agricultural Research Service. Image D827-1: larvae infected with American foulbrood (photo Virginia Williams, public domain). ars.usda.gov

Updated : October 8, 2026
Written by : Apisanitas editorial team
Reviewed by : Review in progress