74. What is American foulbrood?

American foulbrood, often shortened to AFB, is one of the most serious diseases that can affect a beehive. It targets the brood, which means the developing baby bees inside the hive.

For beginners, the name itself can sound worrying—and rightly so. But with a clear understanding, you can recognise it early and take the right steps.

What causes American foulbrood?

AFB is caused by a bacterium called Paenibacillus larvae. This bacterium produces spores, which are extremely tough and long-lasting.

These spores can survive for many years on old equipment, in honey, or even in the hive itself. Bees unknowingly spread them when they clean cells or share food.

Once the spores are inside a young larva, they multiply and eventually kill it.

How does it affect the hive?

AFB mainly affects sealed brood—that is, the stage where the developing bee is capped inside its cell.

As the larva dies, it turns into a sticky, brown substance. Over time, this dries into a hard scale that sticks tightly to the cell.

This creates two problems:

• New bees cannot develop properly

• The infection continues to spread within the hive

If left untreated, AFB can destroy an entire colony.

Signs to look for

One of the most important skills in beekeeping is recognising early warning signs.

With AFB, look for:

• Sunken or perforated caps on brood cells

• A patchy brood pattern (uneven development)

• A brown, sticky larva inside the cell

A common field check is the “rope test”. If you gently insert a small stick into an infected cell and pull it out, the dead larva may stretch out in a rope-like thread.

There may also be a slightly unpleasant smell, though this is not always noticeable.

Why is AFB so serious?

The biggest concern with AFB is how easily it spreads and how long it lasts.

Because the spores are so durable:

• They can remain infectious for decades

• They can spread between hives through robbing or drifting bees

• They can contaminate tools and equipment

For this reason, AFB is considered a notifiable disease in many regions, including Australia.

What should you do if you suspect AFB?

If you think your hive may have AFB, it is important to act carefully and responsibly.

• Do not move frames or equipment to other hives

• Avoid spreading contamination on tools or gloves

• Contact your local beekeeping authority or inspector

In many cases, the recommended action is to destroy the infected hive and equipment to prevent further spread.

A calm and practical outlook

While AFB is serious, it is not something you need to fear constantly.

Regular inspections, good hygiene, and buying bees and equipment from trusted sources greatly reduce your risk.

Think of AFB as something to be aware of, not anxious about. With steady attention and a bit of experience, you will feel confident recognising the signs and protecting your bees.