American Foulbrood Disease – Know it, Identify it, Beat it


As beekeepers, we are responsible for the health of our hives and our apiaries as a whole.  This is three fold.

 First you need to educate yourself on the potential threats to the health of your hives.  

Secondly you need to take the time to regularly and thoroughly examine all the hives in your apiary with particular attention to brood chambers. This includes Flow Hives that offer a convenient honey extraction process sometimes at the expense of the management of the hive as a whole.  You still need to be regularly in the brood boxes of your hives in order to recognise changes in the health of the bees and identify potential problems as early as possible.

Thirdly you need to implement strategies to address any health threat.  Some health issues that a hive can get, if left untreated, can not only kill the hive but potentially, if neglected, can take out your whole apiary.  Worse still even infect other apiaries nearby.

In this article, we are going to take a close look at American Foulbrood Disease.  American Foulbrood Disease of all the potential threats to your hives from diseases and pests is the one that can be the most devastating to your apiary.  Even worse if you do get it, your apiary becomes a threat to other beekeepers around you. 

So what is American Foulbrood Disease?  American foulbrood is a bacterium called Paenibacillus larvae, a brood disease infecting strong and weak hives.  Its spores spread to hives on robber bees or on beekeeping gear. Infected larvae die after the cell has been capped.  American foulbrood is not curable and the hive must be destroyed.

American foulbrood disease does not discriminate, it doesn’t take capitalise on the opportunity the weak hive presents.  It will infect a strong hive just as well as a weak hive.

The scary thing about American foulbrood is that you can be a fastidious beekeeper and still your hive can be infected by this fatal disease.  The best we can do is understand how it operates, identify the symptoms early and act swiftly to eradicate it from your apiary.

American Foulbrood – Know it

What countries have American Foulbrood disease?

American foulbrood can now be found virtually worldwide.  It is not known where the disease originated. What is known is that prior to 1907 the disease was just known as foulbrood.  In 1907 it was discovered there were two types of foulbrood American foulbrood and European foulbrood.  

The name has no reference to geographical origin rather the location of the scientists who discovered the two different types of foulbrood.  

European foulbrood can be effectively treated with antibiotics whereas to date unfortunately there is no cure for American foulbrood. 

American Foulbrood disease lifecycle 

American foulbrood disease is a bacterium called Paenibacillus larvae.  It is a brood disease that has no effect on the health of adult bees, however adult bees can carry the spores.  The spores can also be found in the honey of an infected hive. The spores are not harmful to humans and honey can still be consumed  from an infected hive.

Bee larvae are most susceptible to infection in their first 24 hours with only about 10 spores required for infection.  As the larvae grows bigger it requires more for the infection to take place. After about 4 days the larvae are unlikely to be infected.  The spores are transferred to the larvae by the nurse bees as they feed the larvae.

The spores carried by Nurse bees could have consumed honey containing spores or possibly cleaned out brood cells already infected by American foulbrood.

The spores are consumed in food by the larvae and within 24 to 48 hours they germinate into bacteria in the gut of the larvae.  The bacteria develops into vegetative “rods” that attack the haemolymph and body tissue of the larvae. The larvae ultimately die usually after the cell is capped.

During the final stage of the life cycle the rods form into spores and a lot of them.  There can be as many as 2.5 billion spores contained in a single infected cell. These spores are incredibly resilient and can remain viable for more than 50 years.

The spores can survive heat, direct sunlight, dehydration, desiccation, fermentation, many chemical disinfectants and therapeutic drugs.  They can be found in hive parts, combs, honey and propolis.

Once spores have entered the hive and managed to infect larvae they can multiply rapidly infecting more and more brood.  Bee numbers therefore drop weakening the hive, eventually killing the hive.  

Unfortunately, if there are infected hives within range of your apiary you could be at risk. With this in mind, it is important to understand how American foulbrood is transmitted to other hives.

1. Contaminated equipment

This one is preventable.  Make sure no equipment, frames or boxes from a known infected hive are used or come into contact with another hive in your apiary. It is usually manageable, for the backyard beekeeper.  As a matter of process, the same frames should be put back into the same hives when extracting honey. This is more difficult for commercial beekeepers.  

Contaminated equipment should be burned or alternatively can be irradiated typically for less than the replacement cost of the equipment. Contaminated equipment should never be left lying around in your yard or simply taken to the local rubbish tip.

2. Purchasing hives or bees

If you are purchasing hives from another beekeeper be sure to thoroughly inspect them for all diseases.  What seems like a good deal might blow up your whole apiary if you are not careful. For the same reason, only bee packages from reputable suppliers should be purchased.

3. Robber bees

Robber bees are the most common way the disease is spread and unfortunately this is the one you have the least control over.  If an infected hive is within foraging range of your apiary it poses a threat. As the disease weakens the hive, it will eventually be robbed and yep, bees from your strongest hives are likely to be among the robber bees.  The robber bees will unknowingly be bringing home honey laced with spores. 

Best bet here is to get to know the beekeepers around you, go for a drive around your area or stalk the backyards of your neighbors on google maps in search of other apiaries.  Beekeepers are usually happy to meet other beekeepers.

4. Drift

Drift is another way the disease can spread within your apiary.  If your hives are close together bees can at times return to the hive next door, more often during windy conditions.  If they are loaded with pollen and nectar the guard bees will more often than not let them in. A bee from an infected hive could be carrying spores on their body that can transfer. 

Now we know about American foulbrood disease, let’s look at how we can identify it if we are unlucky enough to have it infiltrate our apiary.

American Foulbrood – Identify it

What is most important here is early identification of American foulbrood.  This will take a keen eye as the early signs before the hive is becoming noticeably weakened as subtle.  The consequences of a weak hive being robbed and the disease spreading can be catastrophic to your apiary.

Let’s take a look at the signs and symptoms you should always be on the lookout for:

1. Reduction of activity at the hive entrance

This could be as a result of any number of factors but should always be of some concern.  The presence of AFB will inevitably be shown in a drop in the activity at the entrance of the hive.

2. Brood cell appearance

American foulbrood is a brood disease so it is the frames in the brood nest that we need to carefully examine.  If you wear glasses to read, like me, make sure you are wearing them when inspecting your hives.  

Infected cells may have a small hole in the cap of the cell.  However it gets tricky because there will be some cells with holes that are healthy and still under construction.  Infected cells may also be sunken, concave in appearance, healthy brood has a slightly convex cell cap. Infected cells may also look slimy in appearance.

3. Brood cell color

The cell cap of the infected brood is dark in color.  The darker color can be identified against the consistent lighter brown caps of the healthy brood.

4. Larvae appearance

Healthy larvae remain white in appearance through to the cell being capped.  The infected larvae on the other hand will change through a range of color as the bacteria rolls through its life cycle.

The freshly emerged larvae are shiny pearl white in color as the American Foulbrood infection takes over the larvae changes through a dull white, yellowish, light brown, coffee brown, to a dark brown, almost black mass.

5. Larvae consistency

The consistency of the larvae also changes from a healthy watery look through syrupy, then ‘ropy’ and pasty stages to a hard, dry, black brittle scale. This process takes about a month to reduce the larvae from nice and plump to a thin hard scale.

6. Irregular brood pattern

Irregular and scattered brood patterns occur in more advanced stages of American foulbrood.  This issue is not exclusive to this disease however when you notice this you should consider American foulbrood as a possible reason.

7. Foul smell

In advanced cases of American foulbrood where there are larger quantities of infected brood cells, the hive will emit an offensive smell. This smell is similar to that of rotting fish. The source of the aroma is the dead larvae in the diseased cells. This is where the term “foul” brood comes from.

The video below is a comprehensive guide to recognize American Foulbrood disease. It is well worth watching.

Testing for American foulbrood disease

If you find these signs and symptoms in your hive you should take some steps to confirm or rule out American foulbrood.

1. Basic field test

If you see brood cells with the above characteristics, take a matchstick or small twig and push it in through the suspected brood cell cap.  If the end of your stick has a coffee colored stringy or ropy larval substance stretching out like chewing gum from the cell, then there is a high probability the cell and therefore the hive is infected with American foulbrood.

2. Secondary field test

At the end of the life cycle of the disease, there will be a hard black scale left in the lower side wall of the cell positioned between about 5 and 7 o’clock.  This can be difficult to see and you may need to hold the frame into direct sunlight to see the scale properly.  

Again take a matchstick or a small twig and try and remove it from the cell.  The scale will be stuck to the wall and impossible to remove without damaging surrounding cells.

3. Scientific field test

American Foulbrood (AFB) field test kits are available at good beekeeping supply stores.  This kit works a bit like a pregnancy test. The sticky coffee like material from an infected cell is a good sample to test. The test reacts with the bacterium confirming its presence in the test material.

It might be worth considering having one of these test kits on hand especially if you don’t have a beekeeping supply shop close to your local area.

Mannlake sells an AFB test kit made by VITA, which looks a bit like a pregnancy test. It will tell you in under 3 minutes of you have AFB present in your beehive.

4. Laboratory testing

Laboratory testing is the most conclusive way to test for the disease. Most local or state agricultural departments will have a lab that does this kind of testing.  For the sample, you provide you can cut out a section of potentially infected comb and send it to the lab.

Another thing you should be aware of is that in some areas around the world American foulbrood is a reportable disease.  You should ask your local authorities if this is the case.

They should not be considered the police and you will not get into strife for having American foulbrood. Authorities will often track instances and look for the source of the disease in the area.  It is very likely that your whole apiary will be quarantined which prohibits you from relocating any of your hives until you are AFB free.

For the backyard beekeeper, this probably does not cause a problem but for the professional, it would be an imposition on your business.  Understandably, AFB should be taken very seriously.

American Foulbrood Disease – Beat it

In order to beat American foulbrood disease sacrifices have to be made.  If you are like most backyard beekeepers you love your hives. In a way that only beekeepers can understand you get to know your hives, like they have their own personalities.  

From experience it is a horrible feeling knowing you are going to have to destroy a hive, even though it may still be a strong hive, for the benefit of your whole apiary.  If you only have one hive then unfortunately it is time to start again and put it down to experience.

Before we go into the process of destroying the infected hive let’s take a look at the precautions you should take to reduce the risk of the disease spreading to your other hives.  Unfortunately beekeepers can easily inadvertently spread it to their other hives.

1. Quarantine of equipment

With just one infected brood cell capable of releasing over a billion spores it is of paramount importance not to cross-contaminate beekeeping tools, frames or supers. Even a hive tool that has been used on a hive with American foulbrood has the potential to infect another hive. 

2. Transferring of combs

It should be common practice to return extracted sticky honey frames to the same hive.  To not do this can spread the disease through spores in the honey or on the frame.  

It is also common beekeeping practices to support weaker hives with frames of brood from the strong hives.  It is important to be certain you are not sharing brood from an infected hive with a healthy hive. Even stored supers or frames of comb can carry infectious spores for many years and infect other hives they are put on at a later date.

The Ultimate Sacrifice

Now for the unenviable task of destroying your infected hive or hives.  Unfortunately this ultimate sacrifice needs to be made for the benefit of the other hives in your apiary. Here is what you need to do in order to beat this resilient disease.

1. Close up the hive

When destroying the hive you need to ensure all the bees are in the hive. Wait until after dark when all the foraging bees have returned to the hive before sealing up the entrance of the hive.

2. Kill the bees

We want this to be quick.  The most common way to do this, after sealing the entrance is to open up the top of the hive and quickly pour gasoline over the frames and immediately close up the hive.  

You will hear a roar from the bees as soon as the gasoline enters the hive.  In less than a minute there will be silence and the bees will be dead. This does not however kill the spores of the American foulbrood disease.  

3. Burn it

Effectively you are going to cremate your hive.  Move the hive to a location where it is safe to burn the hive.  Remember when you light it up it is soaked in gasoline and will be flammable, so be careful.

4. Bury it

Once the hive is burned out it is recommended that the remains are buried at least a foot underground. It is easier if the hive has been burnt in a purpose dug fire pit.

5. Irritate equipment

Any frames, supers and equipment but not honey that has come into contact with American foulbrood can be recovered by sending the equipment to be radiated. The process is used by the agriculture industry to get rid of pests on fruit and vegetables because it is chemical-free and doesn’t damage the produce.  

There is a cost, usually it is pretty economical and time saving if the equipment is in good condition. The upside is that the gear is totally pest free. Radiating kills everything including chalkbrood that also has spores the ability to remain active for up to 15 years.

Alternative treatments for American foulbrood

Over the years there have been other strategies investigated for treating American foulbrood with some limited success.

People have tried shaking out the bees and replacing all combs in the hive with frames of foundation frames.  Returning bees consume the infected honey in their stomach as energy. This is combined with dosing the hive with antibiotics.  There are reports of this being successful however it is risky and a low percentage play that could put other hives in your apiary at risk.

There is currently research being done with probiotics to boost the immune system of bees to make them more resistant to American foulbrood.  This is a link to an article that talks about this. 

The Wrap Up

American Foulbrood is a horrible disease and it is heartbreaking if you discover you have it.  No beekeeper wants to burn hives but this is the sacrifice that has to be made if American Foulbrood is in the hive.

This is why it is so important to be regularly getting into the brood box of your hives and checking the health of your hive.  Also be vigilant in managing your equipment to ensure there is not any potential cross contamination of diseases.

Get to know the beekeepers in your area.  We need to work together sharing experiences and local knowledge when fighting American Foulbrood disease.

Recent Posts