American Foulbrood – A disease that can be eradicated

American Foulbrood - What is it?

American foulbrood (AFB) disease is the most serious brood disease of bees in NSW. It is caused by the bacterium Paenibacillus larvae. In Australia, it has been found in all states. Infection may lead to serious economic loss through the destruction of colonies and loss of production.

It is a notifiable disease under the NSW Apiaries Act 1985. There is a persistent low level of infection in NSW. Early and accurate diagnosis is essential

Spores remain viable in honey for decades, and adult bees can carry spores without themselves becoming diseased. The disease can be rapidly spread by beekeepers, through the interchange of infected combs and hive components between hives and apiaries. Beekeepers can also spread the disease by feeding infected honey or pollen. The disease is also spread by bees stealing honey from infected hives, beekeepers' storage areas, extraction sites and rubbish tips, and by bees drifting from infected colonies into neighbouring colonies. Specific sources of infection can include another nearby apiary, equipment moved to the apiary, or a caught swarm.

Brood should be thoroughly examined for AFB at least twice a year, in spring and autumn. It is also good practice at any time of year to examine colonies that undergo a population decline, to determine if disease is the cause.

Why is it an issue?

  • AFB actively kills bee larvae – more than 95% of infected hives weaken and die out if left alone.
  • Spores survive for more than 40 years (and up to 70 years).
  • In areas with infected hives (feral or managed), there is a high risk to bee colonies within a 3 km radius stealing.
  • AFB requires human intervention to eradicate it from hives or from a district.
  • The use of antibiotics will cause residue contamination and the development of resistance. Antibiotics will not kill the spores.

What can the NSW bee industry do?

  • regular inspection of their hives for AFB
  • controlling and eradicating AFB in their hives
  • seeking and following the advice of livestock officers – bees
  • not feeding antibiotics to AFB-infected colonies.

Beekeepers can obtain accurate diagnoses by sending samples of suspect material to NSW DPI Regional Veterinary Laboratories.

If you receive a positive laboratory report for AFB you are advised to:

  •       • Examine all brood combs in the hives in the infected apiary within 2 weeks, and all other hives owned or managed by you within 6 weeks.
  •       • If you do not think you are able to recognise AFB signs, contact a NSW Department of Primary Industries Apiary Officer or Regulatory Officer for advice.
  •       • Notify an Inspector (regulatory officer) immediately if any hives appear to have suspicious signs.

Keep any hives showing signs of disease isolated from hives that appear healthy. Make sure you do not transfer infection.

  • Do not use infected material in healthy hives.
  • Do not transfer combs or any hive components from diseased to healthy hives.
  • Kill infected colonies as soon as practical and either prepare for irradiation (see Primefact 194 American foulbrood disease – sending beehive material for irradiation) or burn infected material in a hole and cover remains with at least 30 cm of soil. Take note of any fire restrictions.
  • Always handle healthy hives before diseased ones.
  • Do not feed antibiotics to infected hives as this only masks the problem.
  • Always inspect weaker non-performing colonies to determine the reason.
  • Do not expose honey to robber bees.
  • Do not under any circumstances allow infected colonies to die out and allow robber bees access to infected material. This will seriously increase the disease problem in the apiary and surrounding area.

Re-examine your hives every two months to make sure that you have found all the diseased hives.

Examining brood

Remove each brood comb from the colony, and shake or brush most of the bees into the box, or at the entrance, leaving the comb clear for examination. Hold the comb by the top bar, with the light coming over your shoulder, so it shines on the lower sides of the brood cells. Hold the comb at such an angle that the light reaches the base of the cells being examined.

Signs of the disease

  • Brood infected with AFB generally dies after the cells have been capped over and larvae are stretched out on their backs with their heads towards the cell cappings.
  • Affected brood becomes discoloured, turning light brown at first then darker brown as the disease progresses
Figure 1. Healthy sealed brood. American foulbrood affects the sealed brood stage.

Figure 1. Healthy sealed brood. American foulbrood affects the sealed brood stage.

 Figure 2. Brood affected with American foulbrood. The caps on the sealed brood are concave and perforated.

 Figure 2. Brood affected with American foulbrood. The caps on the sealed brood are concave and perforated.

  • After 1 month, infected brood dries to a dark scale which adheres to the wall of the cell. In cases where the mouthparts have developed, that is, when the larva dies at an older age, the fine threadlike tongue of the dead pupa is sometimes attached to the top side of the cell (see Figures 2 and 3). This is a characteristic feature of AFB.

  • Cappings over dead brood cells sink inwards, become moist and have a discoloured dark chocolate or purple appearance. Some of these capped cells are punctured, the result of attempts by bees to remove the dead brood. Other cells may have the cappings totally removed, leaving the remains exposed. These remains are infective.

  • If a matchstick is thrust into the dead brood before the scale stage has developed, and then removed, the semi-fluid remains are drawn out in a ropy thread 3–5 cm long (see Figure 4). This ropy consistency is characteristic of AFB.  

  • In heavily infected colonies the brood has a scattered, uneven pattern due to the intermingling of healthy cells with uncapped cells, and capped cells of dead brood with punctured and sunken cappings. This ‘peppered’ appearance of the brood usually allows AFB to be distinguished from European foulbrood (EFB). In AFB the cappings are discoloured, while in EFB the cappings are not normally discoloured to any great extent.

Figure 3. When the larva first dies the diseased material ropes or strings out when touched with a match. Later the diseased material dries to form a black scale.

Figure 3. When the larva first dies the diseased material ropes or strings out when touched with a match. Later the diseased material dries to form a black scale.

Treatment

Infected materials are either burnt or sterilised using gamma irradiation. In both situations the colony is killed. The two methods of treating AFB-infected materials have been historically very successful in minimising the incidence of this disease in NSW.

The burning of infected materials should be carried out in a pit so as to contain any wax and honey. Local fire restrictions must be adhered to if burning is used to dispose of infected materials. The remaining ashes must be covered with 30 cm of soil.

Sterilisation using gamma irradiation of contaminated hive material is also available. Any honey is removed and extracted. The bees in the infected colonies are killed, then burnt or buried under at least 30 cm of soil. After sterilisation the hive materials are restocked with disease-free bees.

Compensation

Compensation may be payable to a beekeeper whose bees, beehives or appliances are destroyed or irradiated due to AFB in circumstances specified in Part 5 of the Apiaries Act.

Avoiding major disease outbreaks

Beekeepers can and should regularly take action to minimise the potential danger of AFB in their colonies. They should frequently inspect the brood in their colonies.

The use of a barrier system has proven benefits. This can be an apiary barrier or individual hive barrier system. The main form of barrier system in practice is one where the materials (boxes and frames) are kept separate, that is, the boxes of honey removed from an apiary for extraction are returned to that apiary and not another. It is possible to have the same system for single hives where boxes, frames etc. are always placed back on the same hives.

Determining the source of infection

Beekeepers with infected hives should ask themselves appropriate questions to establish a possible source of the infection.

  1. Have you recently purchased or introduced hive material?
  2. Have you treated your colonies with antibiotics or have you provided supplements with honey or pollen as additives?
  3. Have you recently used in the apiary old stored material, e.g. combs?
  4. Are you aware of any neglected and or abandoned hives nearby?
  5. Do you share equipment, e.g. extracting plant?
  6. Can your bees fly to a waste management facility (rubbish tip)?
  7. Can your bees fly to other beekeepers’ extracting sheds?
  8. Do you know of any other apiaries within 3 km and their disease status?
  9. Have you recently caught swarms?
  10. Does your apiary get visited by other beekeepers?

(Compiled with NSWDPI permission from Primefact 209 [American Foulbrood], Primefact 744 [American Foulbrood positive diagnosis- what should you do?], Primefact 759 [American Foulbrood – tracing the source] and Primefact 878 [American foulbrood in NSW]

Author: The Editor - Compiled with permission from NSWDPI Agfacts