American Foulbrood Disease


Photo of bees in a hive. Bees are important for both honey production & pollination servicesAmerican foulbrood disease (AFB) is one of the major diseases of bees in Tasmania. It infects and kills only the larvae, but if left unchecked will affect a hive to such an extent that the honey production will stop and the hive will die out.

Cause

AFB is caused by a bacterium, Bacillus larvae.

Spores of B. larvae are ingested by the larvae with their food. Once ingested the spores multiply rapidly. The larvae then die, usually just after the cells have been capped.

Spread

The disease can be spread in a number of ways.

A hive can become contaminated:
  • when infected bees drift into it.
  • when healthy bees rob an infected hive.
  • when healthy bees are fed contaminated honey.
  • when watering places are contaminated with the bodies of dead bees.
Beekeepers can spread the disease from hive to hive by interchanging combs of brood and honey between infected and healthy hives.

Spread within a hive can occur when house bees clean material from infected cells. They can retain spores of the bacteria on their mouths and spread them to young larvae during feeding.

The use of infected second-hand materials can also spread infection. Spores of AFB can remain viable for up to 30 years.

Symptoms

In its early stage, the first sign of AFB in the hive is the appearance of a few dark, greasy looking, sunken cappings among the healthy brood. Some of these cappings may be perforated. As the disease advances, more diseased cappings will be noticed. In bad cases, it is possible to find 90% of the brood cells infected.

To recognise these infected cells, it is necessary to first learn to recognise healthy brood. The difference between healthy and diseased cells then becomes obvious.

If it is suspected that a cell is diseased, remove the cap and look at the larvae. If it is a glistening white, it is healthy. If it is off-white through to dark brown, and gives the appearance of having been melted down, AFB can be suspected.

After a month or so, the remains will dry out to a dark brown scale on the bottom of the cell. The scale is very difficult to remove and can remain infective for up to 30 years.

To detect dry scales in the cells, hold the comb so that sunlight slants on to the lower sides of the cells. Any scales present will be clearly visible.

A useful guide in the self-diagnosis of AFB is the matchstick test. Insert a matchstick into the cell and withdraw it again. If AFB is present, the remains will stretch out like chewing gum for at least 25mm (an inch). The match used for the matchstick test should always be left in the comb, or burned in the smoker, as it could be heavily contaminated with AFB spores.

Treatment

How diseased hives should be treated depends on the severity of the infection.

In cases of high infection the bees must be destroyed and all frames and combs burnt.

If in good order, the boxes, lids and bottom board may be re-used after the insides are burnt out with a blowlamp so that a thin even char is formed over the whole surface.

In other cases it may be necessary to burn infected frames, replace them with healthy combs and treat with antibiotics.

When burning infected material, it is advisable to dig a pit, start a good fire and place the infected material it. Make sure that no honey or comb is dropped on the ground or left lying around so that bees have access to it. After all infected material has been burnt, the pit should be filled to cover the remains of the fire.

In extremely mild cases, treatment with antibiotics may suffice.

Prevention

Some points to remember in helping to control AFB are:
  • Never allow bees access to honey, cappings, hive scrapings or to dirty, second-hand honey containers.
  • Never interchange combs between hives.
  • Never use second-hand material.
  • Never allow any hive to become neglected. If proper management and maintenance of the hive is no longer possible, sell it or give it away.
  • Always inspect all brood combs each spring for the presence of AFB. Early detection increases the chance of saving the hive form destruction.
  • Always sterilise the hive tool and wash the smoker, hands and/or gloves after working on a hive you may suspect to be infected. This practice is recommended when moving from hive to hive or from apiary to apiary.
  • Never remove a hive with AFB from an apiary site until the infection has been eradicated.
  • Testing honey samples for the presence of AFB spores is a useful management aid.
AFB is a notifiable List B disease under the Animal Health Act 1995. If any beekeeper suspects that they have AFB in their hives they must notify a Department of Primary Industries, Park, Water and Environment stock officer.

A Department stock officer will be able to assist in the diagnosis and treatment of the problem.
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Contact

Biosecurity Tasmania - Apiary Biosecurity
Apiary Biosecurity Coordinator
Biosecurity Operations Branch
Department of Primary Industries, Parks, Water and Environment
GPO Box 44 Hobart 7001
13 St Johns Avenue
New Town TAS 7008
Phone: (03) 6165 3778
Mobile: 0407 436 230
Email: Karla.Williams@dpipwe.tas.gov.au

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