Brood diseases: telling foulbrood from its look-alikes

Seven different things kill or mark honey bee brood, and almost every one of them can look like another. What each is, what it is mistaken for, and why the answer comes from a test — and, for the two foulbroods, a report — rather than from reading the comb.

Bee biologyReviewed 2026-10-30

Why a brood frame cannot diagnose itself

Healthy worker brood is pearly white, plump and curled in a C, and capped in a compact sheet. Almost everything that goes wrong with it shows in the same few ways: gaps in the capped area, larvae that change colour or shape, cappings that sink or are pierced, remains that dry in the cell. Bacteria, a virus, a fungus, a mite and a shortage of nurse bees can each produce some of those signs, and secondary bacteria change how dead larvae look whatever killed them. That is why every serious authority treats a sign as the start of a question.

The four steps from a sign at the hive to an answer, using sunken or pierced cappings as the example. What you see may suggest American or European foulbrood, but sacbrood and brood killed by mites can look similar; the sign cannot confirm which disease it is, or that any is present, because signs overlap and most infections show none. What settles it is a test by an inspector or a laboratory. Where a disease is notifiable — in the UK, both foulbroods — the suspicion is reported before anything else, and nothing is moved from the apiary meanwhile. Sources: Chapter 3.2.2. American foulbrood of honey bees (infection of honey bees with Paenibacillus larvae); Chapter 3.2.3. European foulbrood of honey bees (infection of honey bees with Melissococcus plutonius); Foulbrood disease of honey bees and other common brood disorders; Honey bees: protecting them from pests and diseases. Drawing: HoneyHQ (HEKNO Ltd), original.

The two foulbroods

American foulbrood is caused by the bacterium Paenibacillus larvae, and only its spores infect. A larva can be infected only in its first 53 hours, the median dose in young larvae is about eight or nine spores, and a single dead larva can hold more than a billion. The larva dies after its cell is sealed. The capping becomes moist, darkened, sunken and often pierced; the remains can draw out in a brown thread when a matchstick is pulled from them; and they dry into a scale stuck so tightly to the lower cell wall that it is hard to remove. WOAH's standard distinguishes five genetic types of the bacterium, which differ in how fast they kill larvae, so the same disease does not always look the same.

European foulbrood is caused by a different bacterium, Melissococcus plutonius, and is harder to see. Larvae usually die a day or two before their cell would be sealed, lying twisted in the cell, yellow to brown and melted-looking. Their scales are rubbery and lift out easily, and the smell is sour or absent. Most infected colonies show few signs, the organism persists on comb, and the disease tends to recur. WOAH names a late varroa infestation as an important look-alike, and notes that atypical strains can be sticky enough to resemble the 'rope' of American foulbrood.

The textbook contrast between the two foulbroods, drawn as a brood cell on its side. In American foulbrood (left) the larva dies after the cell is sealed: the capping becomes sunken, darkened and pierced, the remains may draw out in a rope, and they dry into a scale stuck fast to the lower cell wall. In European foulbrood (right) the larva usually dies before sealing, twisted and yellow to brown, rarely ropes, and leaves a rubbery scale that lifts out easily. The contrast is a guide, not a test: atypical strains of European foulbrood can be sticky and rope like American, a late varroa infestation can look like either, and most infected colonies show few signs. Both are confirmed only by a field test or a laboratory, and both are notifiable in the UK. Sources: Chapter 3.2.2. American foulbrood of honey bees (infection of honey bees with Paenibacillus larvae); Chapter 3.2.3. European foulbrood of honey bees (infection of honey bees with Melissococcus plutonius); Foulbrood disease of honey bees and other common brood disorders. Drawing: HoneyHQ (HEKNO Ltd), original.

Telling them apart

The table sets the seven brood conditions side by side: what each can look like, how far that narrows things down, what it is confused with, what confirms it, and whether reporting is a legal duty in the UK nations. Read across a row and the pattern is the same each time. The sign suggests; something else confirms.

Telling brood problems apart: what each can look like, and what settles it
Condition	What you might see	How specific	Can be confused with	What confirms it	Reporting
American foulbrood	A patchy brood pattern; cappings that are moist, darkened, sunken and perforated; remains that may draw out in a brown rope; later, dark scales stuck tightly to the lower cell wall.	Suggestive — still needs a test	European foulbrood, whose atypical strains can also be sticky; Sacbrood; Parasitic mite syndrome	A lateral flow device used by an inspector, or laboratory PCR or culture. In the UK the National Bee Unit confirms it. A matchstick 'rope' test can be negative when the remains are watery, so a negative rope test rules nothing out.	Notifiable: England and Wales; Scotland; Northern Ireland; Ireland
European foulbrood	Larvae twisted in the cell, yellow to brown and melted-looking, dying before sealing; a patchy brood pattern; rubbery scales that lift out easily; a sour smell, or none.	Low — shared with several other causes	American foulbrood; Sacbrood; A late varroa infestation, which WOAH names as an important look-alike; Chilled brood	A lateral flow device, with a result in about ten minutes, or laboratory PCR. WOAH calls field recognition unreliable without specialist training.	Notifiable: England and Wales; Scotland; Northern Ireland; Ireland
Sacbrood	Larvae stretched on their backs in uncapped or part-uncapped cells, the skin a fluid-filled sac, the head end dark and raised — the NBU's 'gondola' shape. The skin can lift out whole.	Moderate — narrows it down, confirms nothing	European foulbrood; American foulbrood	Laboratory testing. A positive RT-PCR result shows the virus is there, not that it caused the dead brood.	Not notifiable in the UK nations or Ireland; elsewhere, ask the national authority
Chalkbrood	Larvae turning spongy and white, then hard and chalk-like, sometimes grey or black once the fungus fruits; mummies in cells, on the floor and at the entrance.	Suggestive — still needs a test	Chilled brood, which it often accompanies	Inspectors recognise it from the mummies. It is not notifiable in the UK, and the sources read describe no routine field test.	Not notifiable in the UK nations or Ireland; elsewhere, ask the national authority
Parasitic mite syndrome	An uneven 'pepper-pot' brood pattern with uncapped, dying pupae; bees with deformed wings; a shrinking population.	Low — shared with several other causes	European foulbrood; American foulbrood; Sacbrood	A mite count showing a high load. Virus testing is a laboratory matter, and rarely needed to act.	Not notifiable in the UK nations or Ireland; elsewhere, ask the national authority
Chilled brood	Brood yellow, brown or black, dried and flaccid, at the edges of the brood nest, with eggs and larvae of every age affected on one comb.	Moderate — narrows it down, confirms nothing	Brood killed by disease — and the fall in population that causes chilling has a cause of its own	No test. It is recognised by where the dead brood is, and the real question is why the population fell.	Not notifiable in the UK nations or Ireland; elsewhere, ask the national authority
Bald brood	Pupae visible in uncapped cells, the cell edges circular and slightly raised, the pupae plump and healthy. Wax moth damage runs in straight lines across the frame.	Moderate — narrows it down, confirms nothing	Brood uncapped because it is diseased — ragged cell edges and unhealthy pupae point there instead	No test. Healthy pupae and smooth cell edges separate it from disease; tunnels and silk point to wax moth.	Not notifiable in the UK nations or Ireland; elsewhere, ask the national authority

A sign narrows the possibilities; it does not settle them. Every condition here has a look-alike, most infections show no sign at all, and finding an organism is not finding the disease. What confirms each one is a test or an inspector, never a reading of comb alone. The reporting column covers only the jurisdictions whose rules HoneyHQ has read — the UK nations and Ireland; it says nothing about anywhere else.

Checked 2026-10-30 against: Chapter 3.2.2. American foulbrood of honey bees (infection of honey bees with Paenibacillus larvae) (WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals); Foulbrood disease of honey bees and other common brood disorders (National Bee Unit, Animal and Plant Health Agency, 2025); Chapter 3.2.3. European foulbrood of honey bees (infection of honey bees with Melissococcus plutonius) (WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals); Sacbrood virus: a growing threat to honeybees and wild pollinators (Viruses 14:1871, 2022); Hygienic behaviour selection via freeze-killed honey bee brood not associated with chalkbrood resistance in eastern Australia (PLOS ONE, 2018); Chapter 3.2.7. Varroosis of honey bees (infestation of honey bees with Varroa spp.) (WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, 2021); Honey bees: protecting them from pests and diseases (Department for Environment, Food & Rural Affairs; Animal and Plant Health Agency, 2024); The Bee Diseases and Pests Control (England) Order 2006 (SI 2006/342), article 2 (legislation.gov.uk, 2006); The Bee Diseases and Pests Control (Scotland) Order 2007 (S.S.I. 2007 No. 506) (legislation.gov.uk, 2007); The Bee Diseases and Pests Control Order (Northern Ireland) 2007 (S.R. 2007 No. 246) (legislation.gov.uk, 2007); Yellow-legged hornet: status, monitoring and reporting (BeeBase) (Animal and Plant Health Agency, National Bee Unit, 2026); Every sighting matters! Why your report matters in the fight against the yellow-legged hornet (Animal and Plant Health Agency (APHA Science blog, GOV.UK), 2026); Wasps (National Bee Unit fact sheet) (Animal and Plant Health Agency, National Bee Unit, 2026); DAERA urges vigilance as Asian hornet monitoring begins in Dundonald (Department of Agriculture, Environment and Rural Affairs (Northern Ireland), 2026); DAERA issues fresh appeal for public vigilance over Asian hornet sightings (Department of Agriculture, Environment and Rural Affairs (Northern Ireland), 2026); Investigation procedures in England (Wildlife Incident Investigation Scheme) (Health and Safety Executive, 2026); Incidents involving pesticides and animals: Wildlife Incident Investigation Scheme (Natural England, Food and Environment Research Agency and HSE, 2012); Honey bee Health Surveillance Programme (guidance document) (Department of Agriculture, Food and the Marine (Ireland), 2020); Infection of honey bees with Paenibacillus larvae (American foulbrood) (Department of Agriculture, Food and the Marine (Ireland), Animal Health Surveillance, 2023); Ireland's response to the Asian hornet 2025: lessons and next steps (National Biodiversity Data Centre, for the Asian Hornet Management Group (Ireland), 2026); Asian hornet (invasives.ie) (National Biodiversity Data Centre (Ireland)).

Sacbrood, chalkbrood and the brood disorders

The National Bee Unit's leaflet records sacbrood, chalkbrood and parasitic mite syndrome as the three commonest diseases its inspectors found between 2006 and 2016. None is notifiable in the UK, and each can be mistaken for one that is.

Sacbrood is a virus. Larvae about two days old are most susceptible; they die after capping, stretched on their backs, the skin a fluid-filled sac with the head end dark and raised — the NBU's 'gondola' shape — and the skin can lift out whole. Infection without signs is common, and a positive laboratory result shows the virus is there, not that it killed the brood.
Chalkbrood is a fungus, Ascosphaera apis. Its spores germinate in the larval gut when brood is chilled below about 32 °C for more than two hours, so it follows weak colonies and cold spells and hits drone brood at the cooler edge of the nest. Larvae turn white and spongy, then hard and chalky, sometimes grey or black. In one Australian survey, colonies bred for hygienic behaviour were no less likely to have it.
Parasitic mite syndrome is varroa with deformed wing virus at a high mite load: a pepper-pot pattern with uncapped, dying pupae, bees with crumpled wings and a shrinking population. The deciding measurement is a mite count, not the brood.
Chilled brood is a disorder. Brood of every age dies at the edge of the nest, yellow, brown or black, when there are too few bees to keep it warm — after a split, a population fall or a cold snap. The question is why the population fell.
Bald brood is a disorder too: pupae develop uncapped, with smooth, slightly raised cell edges and plump, healthy pupae. Lines across a frame point to wax moth larvae tunnelling under the cappings; ragged edges and unhealthy pupae point away from bald brood and towards disease.

The table below gives each condition's cause, how it spreads, why finding the organism is not the same as finding the disease, and what the sources say about honey.

Brood diseases and disorders: cause, spread and what infection means
Condition	Cause	Affects	How it spreads	Infection is not disease	Honey
American foulbrood	Paenibacillus larvae (a bacterium)	Larvae, which die after their cell has been sealed.	Only spores infect. Exchanging comb is the main route between colonies; robbing, feeding spore-laden honey or bee bread, and packages and queens also carry it.	Spores can sit in honey and on comb in colonies with no visible disease. Disease follows when larvae in their first 53 hours swallow enough spores — the median dose in young larvae is about eight or nine.	Honey can carry spores for years without harming the people who eat it. Fed to bees, or left where bees can rob it, it can spread the disease. In the UK, honey may not leave an affected apiary until the disease is controlled. (Described, not quantified.)
European foulbrood	Melissococcus plutonius (a bacterium)	Larvae, which usually die a day or two before their cell would be sealed.	Through contaminated comb within a colony; between colonies by drifting, robbing, equipment and the beekeeper. The organism persists on comb, so the disease tends to come back in later years.	Most infected colonies show few signs, and the bacterium can be found in adult bees and hive products from colonies with no visible disease.	The bacterium can be detected in hive products. The sources read describe effects on the colony, not a measured honey loss. In the UK, honey may not be moved from the site while a suspicion is investigated. (Described, not quantified.)
Sacbrood	Sacbrood virus	Larvae, most susceptible at about two days old; they die after capping.	In brood food from nurse bees. Infection without signs is common.	Infection without signs is common. In the western honey bee it rarely kills a colony, though it has caused losses of 95–100% in the Asian honey bee, Apis cerana.	No effect on honey is described in the sources read. (Not measured in the sources read.)
Chalkbrood	Ascosphaera apis (a fungus)	Larvae, which die after sealing and dry into hard mummies.	Spores swallowed in food germinate in the larval gut when brood falls below about 32 °C for more than two hours. Drone brood, at the cooler edge of the nest, suffers more.	Disease follows chilling of the brood, which is why it goes with weak colonies and cool spells. In an Australian survey, colonies bred for hygienic behaviour were no less likely to have it.	The NBU says it can reduce bee numbers and honey production, though it does not usually kill the colony. (Described, not quantified.)
Parasitic mite syndrome	Varroa destructor with deformed wing virus	Pupae and emerging bees, and in the end the whole colony.	Follows the mite load. The mite injects the virus into developing bees.	Deformed wing virus is carried at low levels by most colonies with varroa. The syndrome appears at high mite loads, when the mites inject the virus into pupae.	The NBU calls it the terminal decline of the colony. No honey measure is given. (Not measured in the sources read.)
Chilled brood	No organism — too few bees to keep the brood warm	Brood of all ages at the edge of the brood nest.	Not infectious. It follows a fall in the adult population, a split made too small, or a cluster contracting in the cold.	Not infectious.	No effect on honey is described in the sources read. (Not measured in the sources read.)
Bald brood	No organism — usually wax moth larvae, or frames set too close	Pupae, which develop uncapped.	Not infectious. Wax moth larvae tunnelling under the cappings, or bees uncapping to make room between frames set too close.	Not infectious.	No effect on honey is described in the sources read. (Not measured in the sources read.)

Reporting, where it is required

In every nation of the United Kingdom, American and European foulbrood are notifiable diseases. A beekeeper who suspects either must tell the bee inspectorate immediately — they do not need to be sure — and must not move colonies, equipment or honey from the site meanwhile. Failing to report is an offence. The table gives each nation's authority and route, the instrument behind it and the date by which HoneyHQ will re-check it.

Who must be told, in each UK nation — and who is only asked
Where	Covers	Duty	When it applies	What to do	Route	Instrument and date
England and Wales	American foulbrood; European foulbrood	Notifiable disease — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell the authority immediately. Do not move colonies, equipment or honey from the site until the disease, if confirmed, has been controlled. Failing to report is an offence.	A local bee inspector, or beehealth.info@defra.gov.uk; colonies registered on BeeBase	Bee Diseases and Pests Control (England) Order 2006 and the Welsh order; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2006. HoneyHQ re-checks this rule by 2027-10-30.
England and Wales	Small hive beetle; Tropilaelaps	Notifiable pest — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell the authority immediately. Do not move colonies, equipment or honey from the site until the authority approves it. Failing to report is an offence.	A local bee inspector, or beehealth.info@defra.gov.uk; colonies registered on BeeBase	Bee Diseases and Pests Control (England) Order 2006 and the Welsh order; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2006. HoneyHQ re-checks this rule by 2027-10-30.
Scotland	American foulbrood; European foulbrood	Notifiable disease — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell the authority immediately. Do not move colonies, equipment or honey from the site until the disease, if confirmed, has been controlled. Failing to report is an offence.	Bees_mailbox@gov.scot or 0300 244 9151; colonies registered on BeeBase	Bee Diseases and Pests Control (Scotland) Order 2007 (S.S.I. 2007/506), articles 2 and 3 read on 30 October 2026, as amended; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2007-12-01. HoneyHQ re-checks this rule by 2027-10-30.
Scotland	Small hive beetle; Tropilaelaps	Notifiable pest — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell the authority immediately. Do not move colonies, equipment or honey from the site until the authority approves it. Failing to report is an offence.	Bees_mailbox@gov.scot or 0300 244 9151; colonies registered on BeeBase	Bee Diseases and Pests Control (Scotland) Order 2007 (S.S.I. 2007/506), articles 2 and 3 read on 30 October 2026, as amended; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2007-12-01. HoneyHQ re-checks this rule by 2027-10-30.
Northern Ireland	American foulbrood; European foulbrood	Notifiable disease — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell DAERA as soon as is reasonably possible — the order's words for a hive's owner or keeper; anyone else who finds a suspected notifiable pest must tell it immediately. Do not move colonies, equipment or honey from the site until the disease, if confirmed, has been controlled. Failing to report is an offence.	beehealth@daera-ni.gov.uk or 028 9052 4168; colonies registered on DataBees	Bee Diseases and Pests Control Order (Northern Ireland) 2007 (S.R. 2007/246), articles 2 and 3 read on 30 October 2026; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2007-05-21. HoneyHQ re-checks this rule by 2027-10-30.
Northern Ireland	Small hive beetle; Tropilaelaps	Notifiable pest — a legal duty	Suspecting it. A beekeeper does not need to be sure.	Tell DAERA as soon as is reasonably possible — the order's words for a hive's owner or keeper; anyone else who finds a suspected notifiable pest must tell it immediately. Do not move colonies, equipment or honey from the site until the authority approves it. Failing to report is an offence.	beehealth@daera-ni.gov.uk or 028 9052 4168; colonies registered on DataBees	Bee Diseases and Pests Control Order (Northern Ireland) 2007 (S.R. 2007/246), articles 2 and 3 read on 30 October 2026; UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2007-05-21. HoneyHQ re-checks this rule by 2027-10-30.
United Kingdom	Varroa	Reportable pest — an official request	Suspecting the mite is present in your colonies.	The guidance says a beekeeper 'should' report it — the word is 'must' for the notifiable diseases — by updating their BeeBase record. No standstill on moving colonies is attached.	The beekeeper's BeeBase record, or the BeeBase report form for those not registered	UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024). From 2024-08-21 (in force at least since the guidance's last update). HoneyHQ re-checks this rule by 2027-10-30.
Great Britain	Yellow-legged hornet	Sightings requested — an official request	Seeing a hornet you think may be a yellow-legged hornet.	Report it with a photograph if one can be taken safely. Do not approach or disturb a nest.	The Asian Hornet Watch app, the UK Centre for Ecology and Hydrology's online form, or alertnonnative@ceh.ac.uk — with a photograph and the location	UK guidance, 'Honey bees: protecting them from pests and diseases' (updated 21 August 2024); National Bee Unit fact sheet on wasps (September 2026); APHA, 9 September 2026. From 2024-08-21 (in force at least since the guidance's last update). HoneyHQ re-checks this rule by 2027-04-30.
Northern Ireland	Yellow-legged hornet	Sightings requested — an official request	Seeing a hornet you think may be a yellow-legged hornet.	Report it with a photograph: DAERA says a sighting cannot be verified without one. DAERA also asks people not to kill or catch other pollinators unnecessarily.	The Asian Hornet Watch app	DAERA press releases of 15 April and 11 September 2026. From 2026-04-15. HoneyHQ re-checks this rule by 2027-04-30.

These are the rules of the United Kingdom and its nations, and of nowhere else. Other countries list different diseases, and a disease notifiable here may carry no duty there, or the reverse. Contact details are as the authority publishes them; the authority's own page is the one to trust if they differ.

Checked 2026-10-30 against: Honey bees: protecting them from pests and diseases (Department for Environment, Food & Rural Affairs; Animal and Plant Health Agency, 2024); The Bee Diseases and Pests Control (England) Order 2006 (SI 2006/342), article 2 (legislation.gov.uk, 2006); The Bee Diseases and Pests Control (Scotland) Order 2007 (S.S.I. 2007 No. 506) (legislation.gov.uk, 2007); The Bee Diseases and Pests Control Order (Northern Ireland) 2007 (S.R. 2007 No. 246) (legislation.gov.uk, 2007); Yellow-legged hornet: status, monitoring and reporting (BeeBase) (Animal and Plant Health Agency, National Bee Unit, 2026); Every sighting matters! Why your report matters in the fight against the yellow-legged hornet (Animal and Plant Health Agency (APHA Science blog, GOV.UK), 2026); Wasps (National Bee Unit fact sheet) (Animal and Plant Health Agency, National Bee Unit, 2026); DAERA urges vigilance as Asian hornet monitoring begins in Dundonald (Department of Agriculture, Environment and Rural Affairs (Northern Ireland), 2026); DAERA issues fresh appeal for public vigilance over Asian hornet sightings (Department of Agriculture, Environment and Rural Affairs (Northern Ireland), 2026).

What the brood diseases mean for honey

Honey is part of the American foulbrood story in a way it is not for the others. Spores survive for years in honey and wax and do not harm people who eat the honey, but bees fed it, or bees that rob it from a discarded jar, can carry the disease home — which is why beekeepers are told never to feed bought honey to bees. The European foulbrood bacterium can also be detected in hive products. The National Bee Unit says chalkbrood can reduce honey production; for sacbrood, parasitic mite syndrome and the disorders, the sources read describe effects on the colony and give no honey figure, and HoneyHQ does not supply one.

The numbers are small where reporting works. The NBU's leaflet records 82 colonies confirmed with American foulbrood in the UK in 2023, 47 of them in England and Wales. That is the point of the reporting duty: a disease found and contained early stays rare.

The claims on this page

Every substantive claim is placed on a tier, and the top two tiers must also state what they are not claiming.

Established evidence

Supported by systematic reviews, meta-analyses or clinical/regulatory guidance. The claim would survive a careful reader checking it.

Established evidence

European foulbrood cannot be reliably recognised in the field without specialist training, and is confirmed by a field test or laboratory rather than by its signs.

The WOAH diagnostic standard states that clinical diagnosis of European foulbrood is unreliable without specialist training, that most infected colonies show few signs, and that a late varroa infestation is an important differential; it describes lateral flow devices and PCR for confirmation.

What this does not claim: It is not a claim that trained inspectors cannot recognise it, nor that any field sign is useless; signs are what prompt the test.

Chapter 3.2.3. European foulbrood of honey bees (infection of honey bees with Melissococcus plutonius) — WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals · Standards document Link

Sources

Chapter 3.2.2. American foulbrood of honey bees (infection of honey bees with Paenibacillus larvae) — WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals · Standards document Link
Chapter 3.2.3. European foulbrood of honey bees (infection of honey bees with Melissococcus plutonius) — WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals · Standards document Link
Foulbrood disease of honey bees and other common brood disorders — National Bee Unit, Animal and Plant Health Agency (2025) · Regulatory guidance Link
Honey bees: protecting them from pests and diseases — Department for Environment, Food & Rural Affairs; Animal and Plant Health Agency (2024) · Regulatory guidance Link
The Bee Diseases and Pests Control (England) Order 2006 (SI 2006/342), article 2 — legislation.gov.uk (2006) · Regulatory guidance Link
Sacbrood virus: a growing threat to honeybees and wild pollinators — Viruses 14:1871 (2022) · Peer-reviewed article Link
Hygienic behaviour selection via freeze-killed honey bee brood not associated with chalkbrood resistance in eastern Australia — PLOS ONE (2018) · Observational study Link
Chapter 3.2.7. Varroosis of honey bees (infestation of honey bees with Varroa spp.) — WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (2021) · Standards document Link
Commission Implementing Regulation (EU) 2018/1882 on the application of certain disease prevention and control rules to categories of listed diseases — European Commission (Official Journal of the European Union) (2018) · Regulatory guidance Link
HoneyHQ editorial synthesis — HEKNO Ltd · HoneyHQ synthesis

How sources are selected and weighted is set out in the sources and evidence policy.

In short

A sign narrows the possibilities; it does not settle them. Brood diseases share signs, and most infected colonies show few.
American foulbrood larvae die after sealing; European foulbrood larvae usually die before. That contrast is a guide, not a test.
WOAH calls field recognition of European foulbrood unreliable without specialist training.
Both foulbroods are confirmed by a field test or a laboratory, and in the UK a suspicion must be reported at once.
Sacbrood, chalkbrood and parasitic mite syndrome were the three commonest brood conditions in NBU inspections between 2006 and 2016.
Chilled brood and bald brood are disorders, not diseases — but chilled brood usually has a cause worth finding.

This guide answers

How do I tell American foulbrood, European foulbrood, sacbrood, chalkbrood and other brood problems apart?

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Brood diseases: telling foulbrood from its look-alikes

Why a brood frame cannot diagnose itself

The two foulbroods

Telling them apart

Sacbrood, chalkbrood and the brood disorders

Reporting, where it is required

What the brood diseases mean for honey

The claims on this page

Established evidence

European foulbrood cannot be reliably recognised in the field without specialist training, and is confirmed by a field test or laboratory rather than by its signs.

Sources

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