Diagnosis, control and eradication of American foulbrood disease
American foulbrood (AFB) is an infectious, notifiable, bacterial brood disease that weakens and kills honey bee colonies.
Early detection of the disease is important because routine apiary management and interchange of hive components can easily spread the disease to healthy bee colonies.
Cause and lifecycle
AFB is caused by the bacterium Paenibacillus larvae. The spores of this organism are too small to be seen by the naked eye and are only visible under a high-powered microscope.
The disease begins in honey bee larvae after they swallow AFB spores with their food. Within 24 to 48 hours, the spores germinate in the gut of the larva and develop into vegetative 'rods'. The rods grow and invade the haemolymph and body tissues, killing the infected larva before pupation, usually immediately after the brood cell is capped.
The final stage of the bacterium's lifecycle is reached when the vegetative rods form into spores. Approximately 2500 million spores may occur in the remains of a single infected honey bee larva.
AFB spores are tough and can remain dormant for 50 years or longer. They can remain dormant on:
- beeswax combs
- used hives and components
They are very resistant to:
- direct sunlight
- chemical disinfectants
- veterinary drugs.
Reducing the risk of AFB
Buying hives with bees
If you are about to buy hives containing bees, inspect all the brood combs to make sure AFB is not present.
The inspection should be done before the hives are paid for and moved to your apiary.
Some beekeepers have not done this and acquired and paid for diseased hives, which they then had to destroy.
Confirmation of AFB can be obtained by laboratory examination of smears of infected larvae. Full details of preparing and submitting samples are found in Samples for laboratory diagnosis of bee diseases.
It is very important to obtain an accurate diagnosis of AFB. If you rely on a fellow beekeeper to inspect the hives for you, make sure they have a good understanding of AFB symptoms and know what to look for. An inaccurate diagnosis can lead to spread of AFB throughout the apiary.
Laboratory culture tests can detect AFB spores in honey even if there are no signs of disease in the brood. If spores have been detected in honey taken from the hives to be purchased, there is a risk that AFB disease could a problem in the future.
Ask the vendor if the hives for sale have been treated with oxytetracycline hydrochloride (OTC), which is an approved antibiotic for the control of European foulbrood but is illegal for the control of AFB. OTC does not kill AFB spores. The spores can remain dormant in the hive ready to start disease after the effect of the antibiotic has worn off.
Keep hives of bees that you have purchased separate from other hives you manage. Some beekeepers who collect swarms keep them separate for several months. In both situations, inspect the brood regularly and if disease is found, take steps to prevent its spread.
Hive components, including combs, should not be interchanged with items from apiaries managed by other beekeepers.
Buying used bee hives and components (without bees)
There is no way of knowing if AFB spores are present on or in second-hand bee hive material. Similarly, the disease history of beehive components that have been in storage for many years may also never be known.
The best course of action is to have the hive material (without bees) sterilised by gamma or X-ray irradiation to remove any doubt as to the disease status of the material. Gamma irradiation will make AFB spores non-viable and unable to cause disease. The sterilised components can then be safely reused.
Gamma irradiation and X-ray irradiation are provided by Steritech in Dandenong and Merrifield in Victoria. Enquiries about this service and preparation of hive material to be irradiated should be directed to Steritech. Telephone: 03 8726 5566.
If you decide not to sterilise previously used hives and components, they should be used in an apiary separate from other hives. Do not interchange hive components with those from other apiaries. Hives should be inspected frequently and if AFB is found steps should be taken to prevent its spread.
Interchange of hive comb between apiaries
AFB may be transferred between apiaries when combs of honey are robbed from one apiary, extracted and then placed on hives of another apiary.
Beekeepers who use a system of barrier management can avoid spreading disease. Case studies of disease barrier management systems are presented the report Honeybee disease barrier management systems.
Sharing honey extracting equipment
AFB spores can be present in honey, including honey on uncapping knives and extractors used by other beekeepers.
If you share extracting equipment with other beekeepers make sure it is clean before you use it.
It is not necessary to sterilise the items, but all traces of honey, beeswax and propolis should be removed and the items thoroughly rinsed with clean water before use.
Feeding bees with honey and pollen
Never feed bees with honey that has not been produced in your own disease-free hives. Honey obtained from other beekeepers and suppliers may contain AFB spores. It is safe to feed bees sugar to keep them alive when honey stores are in short supply.
AFB spores may be present in pollen harvested from infected hives. It is therefore a requirement of Victoria's Livestock Disease Control Regulations 2017 that pollen introduced into Victoria for feeding to bees must be gamma irradiated before or immediately after its introduction.
Agriculture Victoria recommends that all pollen be sterilised by gamma irradiation before feeding it to bees.
Reducing the risk of spread within an apiary
It is important that the AFB is detected early. It takes time to inspect brood and beekeepers need to know the symptoms of the disease. Brood should be inspected:
- in early spring
- in autumn before preparation of hives for winter
- during the season.
In addition to checking brood, a laboratory honey culture test conducted during the beekeeping season can detect AFB spores in extracted honey.
Detection of spores can mean that:
- one or more hives in the apiary are infected
- AFB infection could occur in a hive in the future.
Interchange of hive components between hives within an apiary should not be done unless the hives have already been checked for disease. AFB is easily spread through the interchange of combs and other hive components from diseased hives to healthy hives.
Hives with weak or dead bee colonies should be examined carefully for signs of AFB.
Steps should be taken to prevent robbing and spread to other hives and to nearby apiaries.
Bees that bring AFB into the apiary
As bees have an average foraging range of 3 to 5km, they occasionally rob honey. The honey may contain AFB spores from:
- weak or dead managed and feral honey bee colonies
- unwashed honey containers disposed in the open
- honey extracting facilities that are not bee-proof
- infected hive material not made bee-proof.
Beekeepers cannot prevent their bees from collecting honey from these sources.
Regular inspections of brood and annual honey culture tests are the best way of detecting AFB early and minimising losses of hives, bee colonies and honey production.
Diagnosis of AFB
Inspection of brood
People inexperienced in handling bees and collecting samples should first read Safe beekeeping practices. It is essential that adequate protective clothing is worn, including a bee veil, and techniques for safe handling of bees are understood before opening hives and collecting samples. If you wear glasses to read, wear them while looking for AFB.
Thorough inspections of brood should be conducted:
- in early spring
- during the main honey producing season
- in autumn when hives are prepared for winter.
Additional inspections can be made at the time honey is removed from hives and when hives are requeened.
In healthy colonies, the brood pattern usually appears regular or uniform because the queen has methodically laid eggs across the comb, or in an area formed by a semi-circle or in concentric circles. Sometimes, there may only be a few empty cells interspersed in the area of brood.
The caps of cells containing healthy brood are uniform in appearance, generally bright and convex. Some of these caps may not yet be fully built and consequently appear perforated.
It is always good to look inside these cells to make sure the developing bee is healthy and it is not the beginning of a disease problem.
Symptoms in the combs
The caps of cells containing diseased larvae or pupae may be sunken, concave, dark and at times greasy-looking. Some caps may be perforated (Photo 3) and other caps may be totally removed, exposing the diseased individual.
In colonies with advanced AFB, the brood pattern is irregular or scattered (Photo 4).
There may be many cells which appear empty. However, on closer inspection these cells may contain healthy larvae, sick and decaying larvae, or dried scales which are the remains of larvae.
The comb surface may appear a little greasy. The darker sunken and sometimes greasy caps are scattered among the lighter, convex caps of cells that contain healthy pupae.
In the early stages of AFB, the brood pattern may look entirely normal. This is because AFB is usually slow to establish and only a few larvae will be affected at first. The absence of an irregular brood pattern does not mean that the disease is absent.
Irregular or scattered brood patterns can also occur when other brood diseases are present, or as a result of a failing queen or pesticide damage. It is very important to determine the cause of the scattered brood pattern and to determine if AFB is present.
Symptoms in the brood
Infected larvae change colour from the normal glistening white to off-white, light brown, coffee brown, dark brown and almost black. The colour change occurs after larvae have been capped in their cells. Infected individuals die in capped cells.
AFB diseased larvae and pupae always lie stretched out on their backs on the lower wall of their cells, from the back of the cell (the mid-rib of the comb) to the cell opening. If the cell opening is likened to a clock-face, the diseased individuals (and later scales) will be positioned at the bottom of the face between the figures 5 and 7.
The moist, decaying remains of a dead larva may be 'roped out' of the cell with a match stick of a distance of about 25mm or more (Photo 5). The match is inserted into the tacky larval remains which are then gently picked up (or gently scooped) to be slowly withdrawn from the cell. This matchstick test is a very effective method of diagnosing AFB.
The remains of larvae killed by European foulbrood disease may also stretch out, but usually not as far as AFB diseased larvae. If there is any doubt as to which disease is present, a laboratory diagnosis should be obtained.
Full details of preparing Samples for laboratory diagnosis of bee diseases.
Odour or smell is not a reliable diagnostic tool because some cases of AFB have no discernible smell at all.
Over time, the remains slowly dry to form dark-brown or black scales (Photo 7). In dull light, the scales, being dark, are not easily seen. It is best to hold the frame with the top bar held towards your stomach and tilted to allow sunlight to fall directly onto the lower wall of the cells.
Dried scales do not rope out with the matchstick test. Unlike scales of other brood diseases, they remain firmly attached on the cell wall and are impossible to remove without damaging the cell.
In some outbreaks, tongues of dead pupae may be seen pointing upwards from the remains, almost up to or even touching the roof of the cell (Photos 6 and 7). The presence of tongues is a very reliable AFB field sign, but the absence of tongues is not an indication that AFB is not present in a hive.
Sometimes fully-formed bees that have died just prior to emerging from their cells may be observed with their tongue exposed. This is not a sign of AFB.
Confirmation of AFB
It is important to obtain an accurate diagnosis of AFB. Experience has shown that diagnosis provided by a fellow beekeeper may not always be accurate. An inaccurate diagnosis can lead to spread of the disease throughout the apiary and large losses of hives and honey production.
Confirmation of AFB may be obtained by laboratory examination of smears of infected larvae. Full details are found in Samples for laboratory diagnosis of bee diseases.
Control and eradication of AFB
Hives in which bee colonies have died and hives with reduced adult bee populations that are unable to prevent robber bees from entering should be completely closed. This includes closing the entrance and any other holes that may allow robber bees to gain entry. Robbing of honey is a major cause of disease spread.
Hives that have been closed should be moved to a shaded area away from direct sunlight to prevent meltdown of combs and leakage of honey from the hive.
Extracting honey from AFB infected hives
There is a major risk of spreading AFB if honey is removed and extracted from infected hives. Beekeepers who wish to extract AFB infected honey should discuss this with an apiary officer from the department.
If honey is to be removed from AFB-infected hives for extraction, it must be done before the bees are killed with petrol as described below. It is important that all containers holding this honey are labelled with the words 'AFB honey'. This will enable the honey packer to direct the product to markets that do not require certification that the honey has been produced in apiaries free of AFB.
Preparation before destruction of items by burning
Before destroying items by burning you must enquire at your local council for information on local laws and whether a permit is required to burn hives in the open.
Where hives are on public land apiary sites, contact the local Department of Environment, Land, Water and Planning (DELWP) office to determine if a fire to burn hives will be permitted.
Private land that lies within 1.5km of public land (for example, parks and forests) may be within a Fire Protected Area. The local DELWP office can advise if a fire is permitted on private land in a Fire Protected Area.
Application to burn hives during the declared Fire Danger Period should be made at the local council office. The Fire Danger Period is declared by the Country Fire Authority when the risk of bushfire is high and the start and end of the period will vary across Victoria.
The Fire Danger Period excludes national parks, state forests and other protected public land. If the hives to be destroyed are in a Fire Protected Area on private land, you must obtain a permit from your local DELWP office.
When a permit to burn cannot be granted during a declared Fire Danger Period, the bees should be first killed using unleaded petrol.
The hives infected with AFB can then be bagged using strong plastic bags to make them totally bee-proof. It is wise to consider double bagging infected hives.
They should be then placed in a protected area in a shed, away from sunlight and livestock until a permit can be granted.
Always observe fire restrictions including days of Total Fire Ban.
Preparation of a pit for burning hive material
Burn the diseased combs and hive components in a pit, large enough to accommodate all items and deep enough to retain any melted wax and honey (Photo 8).
Honey and wax that flows out of the pit may be gathered by robber bees and be a source of infection to healthy colonies.
A pit that is deeper at one end than the other allows liquid honey to accumulate away from the seat of the fire and avoids smothering the fire.
The pit should not be dug in low lying areas where storm water may wash soil away and expose any unburnt items that might cause a disease risk to nearby bees.
Sufficient dry wood should be on hand to enable a hot fire to be burning before combs of honey are placed on the fire. This is not necessary when there is little honey present as the combs and wax on hive components will usually generate enough heat to burn the honey.
Killing the diseased honey bee colonies
Infected hives are destroyed by closing all hive exits when the bees have stopped flying. Flight usually stops around sunset, but sometimes much earlier in cold temperatures.
Please discuss this process with an Agriculture Victoria apiary officer prior to destruction. For more information please contact the Customer Service Centre on 136 186 or email firstname.lastname@example.org
Salvage of hive components
Store hive components worth sterilising for later reuse so that robber bees cannot gain access to traces of honey. Boxes should be stacked on a bottom board and covered with a hive lid and then fastened using an Emlock or similar fastener.
Close the hive entrance and seal any other possible entry points, including missing or broken ventilator grids in the cover with durable tape.
Remove any honey present on the outside of these boxes by washing with a wet cloth. Salvaged material must be placed in a bee-proof area until it can be taken for sterilising.
Burning the hives
Use waste wood to start a fire in the pit and continue to add wood so that the fire is well established and hot enough to quickly burn the infected items.
Place the hive components including combs of brood and honey on the fire a few at a time so as not to smother the fire. Add metal lids, bottom boards and queen excluders last.
Take care not to spill honey and comb on the ground where they can remain unburnt and available to robber bees.
When the wooden components have burnt, the hole can be backfilled with the excavated soil. At least 30cm of soil should be placed over the remains of the burn pit.
Actions after the burn
Sterilising hive components by gamma or X-ray irradiation
Gamma and X-ray irradiation are safe and effective ways of sterilising AFB infected hive components. Steritech Pty Ltd in Dandenong South and Merrifield operates the only gamma and x-ray irradiation plants in Victoria. Steritech have full details of price, protocols for presenting hives for irradiation and a Request for irradiation of bee equipment form.
It is usual for hives to be left at the plant and collected after irradiation some days later. Beekeepers should carefully determine the economic benefits of having material irradiated in comparison to destruction of the entire hive. The calculation should include cost of travel and preparation of hive material as required by Steritech.
Beekeepers may be eligible to receive compensation if their bees and/or hives are destroyed or sterilised due to AFB. Compensation is not payable to an unregistered beekeeper or to a beekeeper who failed to notify the presence of field signs of AFB in his or her hives to an apiary officer.
Beekeepers must notify an officer of the presence of AFB before infected bees and hive material is destroyed or irradiated. The officer will advise on how to apply for compensation.
Compensation is paid from the Honey Bee Compensation and Industry Development Fund. The money in the fund is derived from registration fees paid by beekeepers.
Management of the apiary after the initial clean-up of AFB
In many cases, it is an unfortunate fact that after the initial clean-up of AFB infected hives in an apiary, other hives may sooner or later show infection. These occurrences should also be reported to the department.
After the initial clean-up, brood in all the remaining hives should be inspected every 6 to 8 weeks for a period of 12 months to detect any new AFB infection. These inspections are suspended during the cold winter months but they should resume immediately suitable weather occurs in spring.
Brood should also be inspected when taking honey from hives. If AFB is detected in a hive, the honey should not be removed and extracted with combs taken from hives which have no symptoms of AFB.
Samples of honey extracted from healthy hives in the apiary can be laboratory tested to determine if AFB spores are present. The detection of spores may indicate that one or more hives may become diseased at a future time. It is important that the sample where possible contains extracted honey from all the hives in the yard (apiary).
Full details on procedures for collecting and submitting a honey sample for a honey culture test are found in Honey culture tests to detect American foulbrood.
The interchange of hive components, including extracted combs, from an infected apiary to any other apiary managed by a beekeeper will result in the spread of AFB. Barrier management is a system that prevents interchange of material.
Further information can be found in the Rural Industries Research and Development Corporation's publication, Honeybee disease barrier management systems.
Notification is required by the Livestock Disease Control Act 1994. To not notify is to break the law.
Early reporting and recognition of these parasites is one of the most important factors influencing the chance of controlling them and reducing their economic and social impact on the whole community.