Return to Diseases and pests

American Foul Brood, A Disease Of Honey Bees

This page is credited in full to Dave Cushman who created it. His voice is expressed in black colour text and any additions or comments in blue belong to myself. Credit: Dave Cushman’s website.



Foul Brood is a term used to describe two diseases of honey bee larvae, American foul brood (AFB), and European foul brood (EFB). This page deals with American foul brood, which is rare in UK, but must always be born in mind. There is a legal requirement to report AFB.

All beekeepers need to be able to recognise this disease which is strongly infectious as well as the spores being resistant to most sterilising agents except fire or ionising radiation.

For poly units see here: and look for Plastic hives PDF. Current thinking is 3% hypoclorite but this may well change. PH

If you suspect AFB or other brood disease during one of your regular disease inspections, you should contact your local inspector.

The following list is copied directly from a Central Science Laboratory (CSL) booklet.

RULES FOR FOUL BROOD CONTROL 1.Make sure you are familiar with the signs and causes of foul brood and other brood disorders. 2.Inspect your colonies every spring and autumn, specifically to check for brood disease. If you are unsure, seek expert advice. 3.Never transfer combs between colonies, or divide colonies, without first checking for signs of brood disease. 4.Never bring colonies, combs or beekeeping equipment into the apiary unless you are sure that they come from a disease-free source. 5.Never buy old combs. Always sterilise second-hand hives by thoroughly scorching with a blow lamp before use. 6.Control robbing in the apiary. Never leave combs or honey exposed to robbing bees. Never feed honey from another source to your bees. 7.If a colony of bees dies out at any time, seal the hive to prevent the remaining stores being robbed out, pending examination of the brood combs for signs of disease. 8.If any colony appears not to be thriving, and the reason is not already known, examine the brood for signs of disease. 9.Be suspicious of stray swarms. Hive them on foundation rather than drawn comb, and inspect them for disease once they have become established. 10.Regularly and systematically replace old brood combs in the apiary by melting them down and replacing them with frames fitted with foundation.

The National Bee Unit (NBU)operates an apiary inspection programme in England and Wales. This service is free of charge. If disease is suspected, a sample is taken for laboratory analysis and a ‘Standstill Notice’ is issued, which prohibits the removal of bees or equipment from the apiary. If disease is confirmed the inspector returns to carry out the destruction of the colonies.

Examining a colony for brood disease and what to look for…

The objective of this inspection is location of disease or gaining the confidence that it is not present. It should be carried out independently of any other colony management. Use enough smoke to keep the colony subdued. Remove the hive roof and place it on the ground. Any supers that are on the hive can be placed inside the upturned roof which confines the bees. Remove the queen excluder, checking that the queen is not on it. If the brood nest comprises two boxes, examine the bottom one first. Remove an outside comb, this is unlikely to contain brood, place this in a nuc box or lean against the stand leg. Take each comb in turn and remove the adhering bees by giving it a sharp jerk, while holding it by the lugs within the vacant space inside the brood chamber. Combs need to be free of bees in order to see the brood and brood cappings. Examine the brood and cappings for any signs of abnormality, like perforated cappings or discoloured larvae. Look for scales by holding the comb towards the light to illuminate the lower edges of open cells. If there are any abnormal looking cappings, tease the cell open with the corner of your hive tool. Poke a match stick into any dead larval remains in the cell. Dispose of the used match stick by burning in the firebox of your smoker. Repeat the process comb by comb until you have examined the whole brood nest, if no disease is found, reassemble the hive.

Remember that…Healthy larvae are pearly white in colour. Cappings on healthy worker brood can vary from light oatmeal to dark brown. Healthy cappings are dry and slightly convex.

American foul brood is caused by a spore-forming bacterium called Paenibacillus larvae, subspecies larvae. Woodrow established that the larvae become infected between hatching and 24 hrs old when they consume AFB spores in the food they are given. The spores germinate in the gut, becoming bacteria that move into the tissues, where they multiply vigourously. The infected larvae die after their cell is sealed, and millions of infective spores are produced in the remains of their bodies. These remains dry to form scales, which stick tightly to the cell wall and often cannot be removed by the bees. Thus brood combs from infected colonies are heavily contaminated with many millions of spores.

The spores are very resistant to extremes of heat and cold, and to disinfectants. They retain their powers of germination for many years in honey or in old combs and hive equipment.

Once a colony is infected the disease will progress until most of the brood is affected, depriving the colony of new adult bees, causing it to dwindle and then to die out.

Beekeepers are the main agent by which the disease spreads. Any combs, honey or hive equipment transferred from an AFB-infected colony to a healthy colony can and will infect it. Bees robbing honey from infected colonies can also spread the disease. Swarms that issue from infected colonies also carry the infection with them and show the disease after they are hived.

Woodware and appliances can be salvaged by sterilising them by thoroughly… Scorching them with a gas torch.

Clothing, gloves, wellington boots as well as your smoker can be washed in hot soapy water that has had a few crystals of washing soda (sodium carbonate) added to it, then re-washed in ordinary household washing powder to remove the washing soda. Other metal tools like hive tools can be treated a little more aggressively using a solution of detergent, washing soda and a small amount of caustic soda (Sodium Hydroxide), be careful here as the mixture will be caustic, make sure that any buckets that are used to transport the solution have tight fitting lids that do not leak.

Antibiotics are often used in some overseas countries, but this merely masks the disease, rather than curing it, they are not permitted in the UK.

When AFB infected larvae die inside their sealed cell, the appearance of the cell cappings change, They become sunken and some cells may be perforated when worker bees attempt to gain entry to remove the dead larva. The holes in the cappings tend to be jagged and irregular in shape. The cappings may become moist or greasy and darker in colour.

With light infestations only very few cells may show signs of disease, and the colony will appear normal in other respects, the real skill of a beekeeper or inspector is the ability to detect one single infected larva in a comb of several thousand.

More advanced stages of the disease show a pepper pot or ‘shotgun’ brood pattern accompanied by a very unpleasant smell.

As the disease progresses, such that sunken cappings and/or perforated cappings are evident the dead larval remains are light to dark brown in colour, and have a slimy consistency. If a match stick is pushed into the cell and then slowly withdrawn with a twisting motion, the remains can be pulled out in a brown, mucus-like thread or ‘rope’ 9 – 25 mm long. This is called the roping test.

As the disease progresses further the larval remains become more tacky than ropy and gradually dry up with the colour darkening as more moisture is lost.

The proboscis of dead pupae often protrudes upwards from the collapsing corpse.

The final stage of drying leads to the formation of a dark brown or black, granular surfaced, scale which lies on the full length of the lowest portion of the cell.

The scales can be readily detected if the comb is held facing the light, they can be seen, although their colour is almost the same as the cell wall.

Beekeepers can avoid spreading AFB by ensuring that any new cases of disease are recognised before they can spread to other colonies. AFB is an infectious disease and will spread naturally due to robbing and drifting. In practice the main cause of AFB spreading is the beekeeper’s practices of moving combs, frames of brood and bees from one colony to another.

What to do if you suspect foul brood 1.Close the hive 2.Reduce the size of the entrance and take any other steps necessary to prevent the hive being robbed by other colonies 3.Disinfect gloves and beekeeping equipment before examining other colonies 4.Either:

a)?? Contact the NBU to arrange a visit by your local bee inspector

b)?? Send a whole comb containing diseased brood wrapped in several layers of paper and sealed in a cardboard box so that it can not leak honey in transit to the NBU, with a note stating your name and address, the location of the apiary and the identity of the affected hive.

5.You must not remove any hives, bees, or equipment from the apiary until the disease, if present, has been controlled.

Ben Harden, in a post to the Irish List, summed up the infection mechanism…

Foraging bees that rob infected material will unload to hive bees who thus pass on contamination and then if sufficient spores end up on a bee that is provisioning a sub 24 hr old larva the infection becomes established.

Once established the quantity of AFB spores in a colony increases to massive proportions, quickly and so gets to contaminate almost everything including all the stores. Honey then becomes a prime reservoir of infection. Even in a colony with a high level of AFB we still see the odd healthy bees hatching out so one way or another those larvae when under 24 hrs old were provisioned by bees carrying insufficient numbers of spores to cause infection. The LD 50 of AFB is given as 35, i.e. when susceptible larvae are inoculated with 35 spores 50% of them develop the disease.

Bees certainly do not use anything, but an empty cell to store or rear in. A cell that contained an AFB scale is only reused once it has been emptied and cleaned.

AFB spores are in the same family as anthrax and can remain viable for very many years. Which is why it is so important to burn, bury and scorch.

Resistance to AFB can be selected for… In an ABJ article, Steve Taber asks, “What I don’t understand is why beekeepers are so reluctant to work their bees toward resistance to AFB disease?” Steve explains… “The mechanism seems to be that two separately inherited genes are involved. One enables the bearers to detect that capped larvae are in trouble and uncap them. The other stimulates bees to remove the uncapped larvae and evict them before they get to the spore spreading stage.” The same mechanism is effective against chalkbrood, so if you select for bees that are resistant to chalk brood there is a good chance that you won’t see AFB.

Since writing this page, an AFB detection kit has come on the market, which can confirm the presence of disease while still in the apiary.

Leave a Reply