Bacterial brood disease
American Foulbrood (AFB) in the UK
Last updated: 1 May 2026
American foulbrood (AFB) is one of the most serious brood diseases affecting honey bees in the UK. It is a highly infectious bacterial disease caused by Paenibacillus larvae and is classified as a notifiable disease, meaning suspected cases must be reported through the proper channels.
AFB affects developing brood after the cells have been capped. Infected larvae die inside the sealed cell, break down into a sticky brown mass and eventually dry into hard infectious scales that can remain dangerous for many years. Because the spores survive for such a long time, outbreaks can spread through contaminated equipment, honey, robbing behaviour and beekeeper handling.
This guide explains the main signs of AFB, how the ropiness test works, how the disease spreads, and when UK beekeepers should contact a bee inspector.
Key signs of American foulbrood
American foulbrood often shows first as an uneven or “pepper-potted” brood pattern, with healthy sealed brood mixed among empty cells and diseased brood. The sealed cappings may look darker than normal, slightly sunken, greasy or perforated with small holes.
As the disease progresses, infected larvae break down inside the sealed cells and turn brown. When tested carefully with a matchstick, the remains may stretch into a sticky thread, which is known as the ropiness test.
Some colonies may also have a foul, unpleasant or sulphurous smell, but smell should never be relied on by itself. Some confirmed cases show little or no obvious odour, so the brood pattern, cappings and larval condition are more important signs to watch for.
What does American foulbrood look like?
AFB affects sealed brood. Infected larvae die after the cell is capped, turning into a sticky, brown mass that dries into hard scales. The brood pattern often appears uneven or “pepper-potted”.
The ropiness test
Insert a matchstick into a suspect larva and slowly withdraw it. If the remains stretch out in a brown, sticky thread, this strongly indicates AFB.
What to do if you suspect AFB
- Do not move frames or equipment.
- Close the hive and avoid spreading infection.
- Contact a bee inspector immediately.
- Do not attempt to treat or fix the colony yourself.
Read more: When to call a bee inspector.
What causes American foulbrood?
AFB is caused by the bacterium Paenibacillus larvae. The spores can survive for decades and spread through contaminated equipment, robbing, drifting bees, or beekeeper handling.
What not to do
- Do not swap frames between colonies.
- Do not sell or move equipment.
- Do not delay reporting.
American Foulbrood FAQ
Yes. AFB must be reported to the National Bee Unit if suspected.
No. In most cases, infected colonies must be destroyed under official guidance.
AFB affects sealed brood and produces a ropy larval mass, whereas European foulbrood affects unsealed larvae and is not ropy.
Image credits
Disease reference images on this page are courtesy of The Animal and Plant Health Agency (APHA), Crown Copyright.